A review of aquaculture production and health management practices of farmed fish in Kenya

The cellular expression patterns of gdnfa and gdnfb in the gonads of Nile tilapia and their differential response to retinoic acid

In mammals, glial cell derived neurotrophic factor (GDNF) plays a critical role in the self-renewal and maintenance of spermatogonial stem cells (SSCs) in testis and oogenesis in ovary, whilst retinoic acid (RA), the key factor of meiosis initiation, can downregulate its expression. Unlike mammals, two Gdnf replication genes are widely present in teleost fishes, however, our understanding of them is still poor. In the present study, two paralogous gdnf from Nile tilapia (Oreochromis niloticus), namely as Ongdnfa and Ongdnfb, were characterized, and then their cellular expression profiles in testis and ovary and responsiveness to RA treatment at the tissue and cellular levels were investigated. In phylogenetic tree, the Gdnfa and Gdnfb from teleost fishes were clustered into two different subclasses, respectively, and then clustered with the homologs from cartilaginous fish and tetrapods, suggesting that OnGdnfa and OnGdnfb are orthologous to GDNF and paralogous to each other. Ongdnfa is expressed in Sertoli cells and Leydig cells in testis and oocytes in ovary. The expression pattern of Ongdnfb is similar to Ongdnfa. In the ex vivo testicular organ culture, RA down-regulated the expression of Ongdnfa, whereas up-regulated the expression of Ongdnfb (P < 0.05), suggesting that they have differential responsiveness to RA signaling. RA treatment of the cultured cells derived from adult Nile tilapia testis which have the expression of RA receptors (RAR), Ongdnfa and Ongdnfb further confirmed the above result. Collectively, our study suggests that Ongdnfa and Ongdnfb have non-germline expression patterns in testis and germline expression patterns in ovary; furthermore, they have differential responsiveness to RA signaling, implying that they might have differential biological functions. This study broadens and enriches our understanding of fish GDNF homologs and lays foundation for the study of their biological functions in the future.

Evaluation of the antibacterial activity and protein profiling of Nile tilapia (Oreochromis niloticus) epidermal mucus under different feeds and culture systems (biofloc technology and earthen pond)

The mucus layers of fish serve as the main interface between the organism and the environment. They play an important biological and ecological role. The current study focuses on Nile tilapia epidermal mucus reared under different commercial feeds (coded A and B) and environments (biofloc technology and earthen pond systems). Crude protein levels in feed A and B were 30% and 28%, respectively. Water parameters in all culturing systems were suitable for tilapia throughout the study period. The antimicrobial potency of tilapia (n = 5 from each) epidermal mucus was tested in vitro against human and fish pathogenic strains viz. Staphylococcus epidermidis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Francisella noatunensis, and Aeromonas hydrophila. To determine the antimicrobial activity, zones of inhibition (ZOI) were measured in millimetres and compared with two antibiotics (chloramphenicol and ciprofloxacin). SDS-PAGE analysis was performed on skin mucus samples of tilapia to determine protein quantity and size (molecular weight). Results of tilapia skin mucus (crude and aqueous) revealed a strong antibacterial effect against all the selected pathogenic strains. However, variation has been observed in the mucus potency and ZOI values between the biofloc and pond tilapia mucus. The crude mucus of tilapia fed on feed A and cultured in the pond exhibited strong antibacterial effects and high ZOI values compared to the mucus of biofloc tilapia, aqueous mucus extracts and positive control chloramphenicol (antibiotic). The SDS-PAGE results showed that the high molecular weight proteins were found in the collected epidermal mucus of BFT-B (240 kDa) and EP-B (230 kDa). Several peptides in fish skin mucus may play a crucial role in the protection of fish against disease-causing pathogens. Thus, it can be utilized in the human and veterinary sectors as an 'antimicrobial' for treating various bacterial infections.

Using geophysics to guide the selection of suitable sites for establishing sustainable earthen fishponds in the Niger-Delta region of Nigeria

Water retention in earthen fishponds throughout a fish farming cycle is challenging due to climate-induced water loss via evapotranspiration, seepages, and lowering of the groundwater table. These processes depend on the soil hydrostratigraphic condition and constitute a major challenge for fish farmers in the Niger-Delta region of Nigeria, where seasonal variations cause groundwater levels to fluctuate. This study assesses the use of non-invasive geophysical methods, including electrical resistivity and induced polarization, to guide the selection of sites with appropriate hydrostratigraphic conditions for establishing earthen fishponds. We combined measurements of electrical resistivity and chargeability distributions to assess the subsurface of two earthen fishpond sites at Ugono-Abraka and Agbarha-Otor areas in the Niger-Delta region of Nigeria. Electrical soundings were acquired at ten locations, while two-dimensional electrical resistivity and Induced polarization were acquired across five transects using Schlumberger and dipole-dipole electrode configurations. The field data were inverted using IP2win, and Diprowin software. The geophysical models were combined with lithological data from soil cores to characterize the subsurface stratigraphy, while measured clay contents were used to estimate infiltration coefficients relying on established petrophysical relationships. The delineated subsurface properties at Ugono-Abraka and Agbarha-Otor show higher variations than assumed by practitioners. The complementary results of low resistivity (20-140 Ωm) and high chargeability (10-50 msec) revealed areas with clay-rich sediments. Soil samples confirmed higher clay contents of up to 10% at Ugono-Abraka and low values of 2% at Agbarha-Otor. Estimated infiltration coefficients are lower at the Ugono-Abraka site (1.6 m/day) compared to Agbarha-Otor (8.4 m/day). This implies variable water loss in the earthen fishponds; hence, we recommend characterizing these variations using non-invasive geophysical methods before establishing medium to large-scale earthen fishponds in the area.

Greenhouse Gas Emissions Associated with Nile Tilapia (Oreochromis niloticus) Pond Fertilization in Western Kenya

In the recent past, fish farming has gained great prominence in Kenya as the country straggles to meet food security. Nile tilapia (Oreochromis niloticus L.) farming has attracted the most demand, with the use of manure to enhance primary productivity in fish ponds being encouraged as a form of increasing productivity and returns on investment. The objective of this study was to understand the role of Nile tilapia farming in greenhouse emissions (GHGEs) in the region. Generally, there is paucity of such information originating from sub-Saharan Africa. Here, we report the levels of methane (CH₄), carbon dioxide (CO₂), and nitrous oxide (N₂O) emissions from Nile tilapia fish ponds fertilized with organic and inorganic fertilizers. We also try to establish if there exists any relationship between GHGEs and physicochemical parameters (PCPs). The methane fluxes ranged from 0.001 to 0.043°mg·m^-2h^-1 in UF ponds, 0.005 to 0.068°mg·m^-2h^-1 in IF ponds, and 0.001 to 0.375°mg·m^-2h^-1 in OF ponds. The findings show that the fluxes were significantly different (P < 0.05). Mean fluxes of CO₂ did not show significant difference among the treatments (P > 0.05), ranging from -0.180 to 1.40°mg·m^-2h^-1 in UF ponds, -0.020 to 1.101°mg·m^-2h^-1 in IF ponds, and -0.049 to 1.746°mg m^-2h^-1 in OF ponds. N₂O mean fluxes were not significantly different (P > 0.05), ranging from -0.628 to 0.326°µgm^-2h^-1 in UF ponds, -0.049 to 0.187°µgm^-2h^-1 in IF ponds, and -0.022 to 1.384°µgm^-2h^-1 in OF ponds. UF had a mean flux of -0.003 ± 0.175°µgm^-2h^-1, IF had a mean flux of 0.032 ± 0.056°µgm^-2h^-1 and OF had a mean flux of 0.093 ± 0.324°µgm^-2h^-1. There was significant difference in the carbon to nitrogen (CN) ratio among the fertilization treatments (P < 0.05), whereas temperature, pH, dissolved oxygen, and conductivity showed no significant difference among the fertilization treatments (P > 0.05). The study observed that fertilization of Nile tilapia ponds significantly increases the release of CH₄ emission and the CN ratio. Temperature, conductivity, and CN positively correlated with CH_4, CO₂, and N₂O emissions. Dissolved oxygen showed a negative correlation with CH₄ and CO₂ emissions while negatively correlated with N₂O emissions. The study identified the use of OF as a potential form of fish farming that promotes the emission of GHGEs and calls for adoption of sustainable technologies for the management of organic and inorganic fertilizers before their use in pond fertilization.

Dietary powder and molecular imprinted polymer nanoencapsulated sodium propionate to enhance growth performance, digestive enzymes activity, antioxidant defense, and mucosal immune response in African cichlid (Labidochromis lividus) fingerlings

This study was conducted to examine the effects of powder sodium propionate (P-SP) and SP-loaded molecular imprinted polymer (MIP) nanoparticles (MIP-SP NPs) on the growth, skin mucosal immune parameters, and digestive and liver enzymes activities of African cichlid (Labidochromis lividus) fingerlings. Fish with an average weight of 500±2 mg were stocked into 12 experimental units and fed on experimental diets prepared by supplementing the basal diet (control) with MIP NPs, P-SP (5 g SP Kg-1 of dry diet), and MIP-SP NPs for 8 weeks. The findings demonstrated that growth indices improved in the MIP-SP NPs followed by the P-SP dietary group compared to the control groups (P<0.05). The activity of digestive enzymes of lipase, trypsin, protease, and alkaline phosphatase was higher in the fish fed SP-supplemented diets than in the controls (P<0.05). The protease and lipase activities in the MIP-SP NPs dietary group increased by 29.33% and 48.81% compared to the control, respectively (P<0.05). In addition, the alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels of liver tissue decreased in the SP dietary groups, while the catalase (CAT), superoxide dismutase (SOD), and alkaline phosphatase (ALP) levels increased compared to the control groups (P<0.05). The highest SOD and ALP levels were observed in the fish fed on the MIP-SP NPs-supplemented diet (P<0.05). Furthermore, the skin mucosal immune indices including, alternative haemolytic complement activity (ACH50), lysozyme, and total immunoglobulin (Ig) levels increased in the MIP-SP NPs and P-SP dietary groups compared to the controls (P<0.05). The findings indicated that sodium propionate encapsulated in molecularly imprinted polymer nanoparticles could enhance the efficiency of dietary SP in African cichlid fish.

Dietary Cinnamaldehyde Enhances Growth Performance, Digestion, Immunity, and Lipid Metabolism in Juvenile Fat Greenling (Hexagrammos otakii)

Fat greenling (Hexagrammos otakii) is a kind of economic fish that is widely consumed by human, and its intensive farming technology is making important progress. However, high-density farming may cause the occurrence of diseases in H. otakii. Cinnamaldehyde (CNE) is a new feed additive for aquatic animals and has a positive effect on disease resistance. In the study, dietary CNE was evaluated on the growth performance, digestion, immune response, and lipid metabolism of juvenile H. otakii (6.21 ± 0.19 g). Six experimental diets were formulated containing CNE at levels of 0, 200, 400, 600, 800, and 1000 mg/kg for 8 weeks. The percent weight gain (PWG), specific growth rate (SGR), survival (SR), and feeding rate (FR) were significantly increased by including CNE in fish diets regardless of the inclusion level (P < 0.05). The feed conversion ratio (FCR) was significantly decreased among the groups fed CNE supplemented diets (P < 0.05). A significant decrease in hepatosomatic index (HSI) was observed in fish fed 400 mg/kg-1000 mg/kg CNE compared to the control diet (P < 0.05). Fish-fed diets containing 400 mg/kg and 600 mg/kg CNE had a higher level of crude protein in muscles than the control diet (P < 0.05). Moreover, the activities of lipase (LPS) and pepsin (PEP) in the intestinal were markedly increased in juvenile H. otakii-fed dietary CNE (P < 0.05). Apparent digestibility coefficient (ADC) of dry matter, protein, and lipid was significantly increased with CNE supplement (P < 0.05). The activities of catalase (CAT) and acid phosphatase (ACP) in the liver were markedly enhanced by including CNE in juvenile H. otakii diets compared with the control (P < 0.05). The activities of superoxide dismutase (SOD) and alkaline phosphatase (AKP) in the liver were markedly enhanced in juvenile H. otakii treated with CNE supplements 400 mg/kg-1000 mg/kg (P < 0.05). Additionally, the levels of total protein (TP) in the serum were markedly increased by including CNE in juvenile H. otakii diets compared with the control (P < 0.05). In the CNE200, CNE400, and CNE600 groups, albumin (ALB) levels in the serum were markedly higher compared with that in the control (P < 0.05). In the CNE200 and CNE400 groups, the levels of immunoglobulin G (IgG) in the serum were significantly increased compared with that the control group (P < 0.05). The juvenile H. otakii-fed dietary CNE had lower triglycerides (TG) and total cholesterol (TCHO) levels in the serum than fish-fed CNE-free diets (P < 0.05). The gene expression of peroxisome proliferator-activated receptor alpha (PPAR-α), hormone-sensitive lipase (HSL), and carnitine O-palmitoyltransferase 1 (CPT1) in the liver was significantly increased by including CNE in fish diets regardless of the inclusion level (P < 0.05). However, fatty acid synthase (FAS), peroxisome proliferator-activated receptor gamma (PPAR-γ), and acetyl-CoA carboxylase alpha (ACCα) in the liver were markedly decreased with CNE supplements 400 mg/kg-1000 mg/kg (P < 0.05). The glucose-6-phosphate1-dehydrogenase (G6PD) gene expression levels in the liver were markedly decreased compared with the control (P < 0.05). The optimal supplementation level of CNE was shown by curve equation analysis to be 590.90 mg/kg.

A systematic review and meta-analysis of the relationship between farm management, water quality and pathogen outbreaks in tilapia culture

A systematic review and meta-analysis of on farm management and water quality as risk factors triggering pathogen outbreaks in tilapia culture is presented. A total of 121 papers from 28 countries, 37 devoted to management and 84 to water quality associated with the presence of pathogens in tilapia culture were analysed. Most of research has been made on ponds, focusing on bacteria and metazoans. Meta-analysis reveals the proportion of research showing statistical inferences between management (34%), water quality (38% for bacteria and 16.2% for metazoans) and pathogen outbreaks. The most cited parameters related to pathogens outbreaks were temperature (>30°C), dissolved oxygen (<5.0 mg/L), pH (<8.0) and ammonia (1.0 >mg/L) 65, 38, 32 and 34 papers, respectively. However, statistical inference was <20%. Meta-analysis reveals tendencies between high temperatures (30-35°C), low dissolved oxygen (<5 mg/L) and high NH₃ (1-5 mg/L) with pathogen outbreaks. Despite the knowledge about the relationship between management and water quality as factors for pathogen effects, most information is descriptive and empirical. Future research on tilapia culture outbreaks should be focused on the effects of multiple stressors affecting tilapia pathogen outbreaks, thereby generating strategies to prevent diseases and financial losses.

Economic feasibility study of aerators in aquaculture using life cycle costing (LCC) approach

Selection of aerator is a very important aspect in aquaculture operations. The selected aerator must be economically efficient and should be able to fulfil the requirement of oxygen supply in the pond water. In the present study, economic feasibility of nine different types of aerators, namely, perforated pooled circular stepped cascade (PPCSC), pooled circular stepped cascade (PCSC), circular stepped cascade (CSC), paddle wheel (PWA), spiral aerator (SA), propeller-aspirator-pump (PAA), submersible (SUBA), impeller aerator (IA) and air-jet aerator (AJA) was assessed based on capitalization method, a life cycle costing (LCC) approach. The results revealed that the PPCSC aerator can be considered as the most suitable aerator when dissolved oxygen (DO) content in the pond water is less than equal to 3 mg/L, and pond water volume (V) is less than 2100 m³. In other situations, mostly when pond water volume is more, IA proves to be the most suitable aerator, followed by PWA, PPCSC, and other available aerators. The sensitivity analysis conducted by using varying stocking density and capital cost also showed the same trend with regard to selection of aerators. This life cycle costing approach for selection of aerator can be implemented for any types of cultured species at any prevailing environmental conditions.

Lernaea cyprinacea Linnaeus, 1758 (Copepoda: Lernaeidae) infection on Betta rubra Perugia, 1893 (Anabantiformes: Osphronemidae) from Aceh Province, Indonesia

Betta rubra is an ornamental freshwater fish endemic to northern Sumatra, Indonesia. The B. rubra population has decreased in recent decades, and is classified as an endangered species in the IUCN Red List. This study aims to report for the first time infection by L. cyprinacea in B. rubra harvested from the Aceh Besar region of Indonesia. The fish samples were obtained from the Cot Bira tributaries, Aceh Besar District, Indonesia from January to December 2020. The results showed that the parasite infected 6 out of 499 samples in August and September, with a prevalence and intensity rate of 1% and 2 parasites/fish, respectively. The eyes and pectoral fins were the common infection sites. Despite B. rubra is not an optimal host (small size) for the parasite, this parasite might serve as additional threatening factors for the endangered B. rubra fish population.

The future of fish in Africa: Employment and investment opportunities

One of the most pressing challenges facing food systems in Africa is ensuring availability of a healthy and sustainable diet to 2.4 billion people by 2050. The continent has struggled with development challenges, particularly chronic food insecurity and pervasive poverty. In Africa's food systems, fish and other aquatic foods play a multifaceted role in generating income, and providing a critical source of essential micronutrients. To date, there are no estimates of investment and potential returns for domestic fish production in Africa. To contribute to policy debates about the future of fish in Africa, we applied the International Model for Policy Analysis of Agriculture Commodities and Trade (IMPACT) to explore two Pan-African scenarios for fish sector growth: a business-as-usual (BAU) scenario and a high-growth scenario for capture fisheries and aquaculture with accompanying strong gross domestic product growth (HIGH). Post-model analysis was used to estimate employment and aquaculture investment requirements for the sector in Africa. Africa's fish sector is estimated to support 20.7 million jobs in 2030, and 21.6 million by 2050 under the BAU. Approximately 2.6 people will be employed indirectly along fisheries and aquaculture value chains for every person directly employed in the fish production stage. Under the HIGH scenario, total employment in Africa's fish food system will reach 58.0 million jobs, representing 2.4% of total projected population in Africa by 2050. Aquaculture production value is estimated to achieve US$ 3.3 billion and US$ 20.4 billion per year under the BAU and HIGH scenarios by 2050, respectively. Farm-gate investment costs for the three key inputs (fish feeds, farm labor, and fish seed) to achieve the aquaculture volumes projected by 2050 are estimated at US$ 1.8 billion per year under the BAU and US$ 11.6 billion per year under the HIGH scenario. Sustained investments are critical to sustain capture fisheries and support aquaculture growth for food system transformation towards healthier diets.

Aquaculture wastewater treatment through microalgal. Biomass potential applications on animal feed, agriculture, and energy

The use of microalgae to remediate raw effluent from brown crab aquaculture was evaluated by performing batch mode growth tests using separately the microalgae Chlorella vulgaris (Cv), Scenedesmus obliquus (Sc), Isochrysis galbana (Ig), Nannocloropsis salina (Ns), and Spirulina major (Sp). Removal efficiencies in batch growth were 100% for total nitrogen and total phosphorus for all microalgae. Chemical oxygen demand (COD) remediations were all above 72%. Biomass productivity varied from 20.9 mg L^-1 day^-1 (N. salina) to 146.4 mg L^-1 day^-1 (C. vulgaris). The two best performing algae were C. vulgaris and S. obliquus and they were tested in semi-continuous growth, reaching productivities of 879.8 mg L^-1 day^-1 and 811.7 mg L^-1 day^-1, respectively. The bioremediation of the effluent was tested with a transfer system consisting of three independent containers and compared with the use of a single container. The single container had the same capacity and received weekly the same volume of effluent as the three containers together. The remediation capacity of the 3 containers was much higher than the single one. The supplementation with NaNO₃ was tested to improve the nutrient removal microalgae' capacity, with positive results. The removal efficiencies were 100% for total nitrogen and total phosphorus and higher than 96% for COD. The obtained C. vulgaris and S. obliquus biomass were composed of 31 and 35% proteins, 6 and 8% lipids, 39 and 30% carbohydrates, respectively. The composition of these biomass suggest that it can be used as novel and sustainable ingredients in aquaculture feeds. The algal biomass of Cv and Sc were used as biostimulants in the germination of wheat and watercress, and very promising results were attained, with increases in the germination index for Cv and Sc of 175% and 48% in watercress and 84% and 98% in wheat, respectively. The biomasses of Cv and Sc were also subjected to a torrefaction process with 72.5 ± 1.7% char yields. The obtained biochars were tested as biostimulants for germination seeds (wheat and watercress) and as bio-adsorbent of dye solutions.

Nutrient loading and farm characteristics of giant gourami fish aquaculture systems in Lake Maninjau, Indonesia: basic knowledge of production performance

Background Aquaculture systems for giant gourami, Osphronemus goramy Lacepède (1801), have significantly improved fish production yields and food security in Indonesia. However, these systems also cause serious problems in terms of eutrophication in waterbodies. This study analysed the nutrient loading and farm characteristics of giant gourami in floating cages in Lake Maninjau. Method A total of 20 floating cages were used to record these nutrients in feed supply, female and male juvenile fish, dead fish and harvested fish to estimate nutrient loading. Data on the harvested fish, production cycle, stock number and cage capacity were used to estimate the stocking density, feeding rate, feed efficiency, and net fish yield, and the relationship between feed supply and nutrient loading and farm characteristics was analysed by least squares regression methods. Results A total of 20 floating cages released nutrients into waterbodies at an average rate of 236.27±60.44 kg/cycle for C, 84.52±20.86 kg/cycle for N and 8.70±3.63 kg/cycle for P. On average, fish production for each floating cage (±SD) was 1226±282 kg wet weight/cycle, and the net fish yield was 12.63±2.82 kg/m 3/cycle. Survival rates ranged from 86.33 to 95.27%/cycle. The production cycles varied from 160 to 175 days with feed conversion ratios between 1.60 and 1.75, feed conversion efficiencies were between 0.58 and 0.63. The production parameters that had strong relationships with the net fish yield were feed supply ( r2=0.960), stocking rates ( r2=0.924) and feeding rates ( r2=0.961). In contrast, the length of the production cycle was not strongly related to the net fish yield ( r2=0.187). Conclusion Nutrient loading from the supplied feed was greater than that from the harvested fish, juvenile fish and dead fish. Increasing the net fish yield in floating cages was better predicted by the stocking densities and feeding levels than by the other factors.

Alteration of the Immune Response and the Microbiota of the Skin during a Natural Infection by Vibrio harveyi in European Seabass (Dicentrarchus labrax)

Disease outbreaks continue to represent one of the main bottlenecks for the sustainable development of the aquaculture industry. In marine aquaculture, many species from the Vibrio genus are serious opportunistic pathogens responsible for significant losses to producers. In this study, the effects on the immune response and the skin microbiota of European sea bass (Dicentrarchus labrax) were studied after a natural disease outbreak caused by V. harveyi. Data obtained from infected and non-infected fish were studied and compared. Regarding the local immune response (skin mucus) a decrease in the protease activity was observed in infected fish. Meanwhile, at a systemic level, a decrease in protease and lysozyme activity was reported while peroxidase activity showed a significant increase in serum from infected fish. A clear dysbiosis was observed in the skin mucus microbiota of infected fish in comparison with non-infected fish. Moreover, V. harveyi, was identified as a biomarker for the infected group and Rubritalea for healthy fish. This study highlights the importance of characterizing the mucosal surfaces and microbial composition of the skin mucus (as a non-invasive technique) to detect potential disease outbreaks in fish farms.

Innovative Technologies to Promote Sustainable Recirculating Aquaculture in Eastern Africa-A Case Study of a Nile Tilapia (Oreochromis niloticus) Hatchery in Kisumu, Kenya

Lake Victoria, regionally important both as a source of food and income, is under pressure due to overfishing and severe pollution. Currently, the vast majority of east African aquaculture is open-pond based. The adoption of modern and sustainable aquaculture technologies and practices-in this case study recirculating aquaculture systems (RAS)-will help the region increase food security and decrease its current reliance on imported fish and stressed wild stock. To this end, VicInAqua, a project under the EU Horizon 2020 program, has developed a pilot Nile Tilapia (Oreochromis niloticus) hatchery in Kisumu, Kenya using RAS adapted to local conditions. The hatchery is designed as a flexible, scalable, and modular system. An online monitoring system enables farmers to access farm data from both fish tanks and the supporting renewable energy systems, allowing around-the-clock monitoring and control. The hatchery is linked to a 14.3 kWp Photovoltaic (PV) system, including a 30 kWh Li-battery storage, to supply sustainable electricity. The water for the RAS, treated by a membrane bioreactor (MBR) and certified for use in aquaculture and agriculture, comes chiefly from Kisumu's municipal sewage, which reduces the farms' reliance on an expensive and occasionally intermittent potable water supply. Combining these technologies represents an industry first and offers a working example for larger-scale future developments. The purpose of the project is to demonstrate the possible technologies and practices in situ as well as provide a template for future development and investment. The hatchery is used by the Department of Livestock, Agriculture and Fisheries, Kisumu County, Kenya, as a training and demonstration facility to promote the aquaculture sector and increase the awareness, knowledge, and skills of fish farmers, as well as provide high quality fingerlings to cage farmers within the lake. Integr Environ Assess Manag 2020;16:934-941. © 2020 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

A review of the socioecological causes and consequences of cyanobacterial blooms in Lake Victoria

Africa is experiencing high annual population growth in its major river basins. This growth has resulted in significant land use change and pollution pressures on the freshwater ecosystems. Among them, the Lake Victoria basin, with more than 42 million people, is a unique and vital resource that provides food and drinking water in East Africa. However, Lake Victoria (LV) has experienced a progressive eutrophication and substantial changes in the fish community leading to recurrent proliferation of water hyacinth and cyanobacteria. Based on an extensive literature review, we show that cyanobacterial biomasses and microcystin concentrations are higher in the bays and gulfs (B&Gs) than in the open lake (OL), with Microcystis and Dolichospermum as the dominant genera. These differences between the B&Gs and the OL are due to differences in their hydrological conditions and in the origins, type and quantities of nutrients. Using data from the literature, we describe the multiple ways in which the human population growth in the LV watershed is connected to the increasing occurrence of cyanobacterial blooms in the OL and B&Gs. We also described the consequences of cyanobacterial blooms on food resources and fishing and on direct water use and water supply of local populations, with their potential consequences on the human health. Finally, we discuss the actions that have been taken for the protection of LV. Although many projects have been implemented in the past years in order to improve the management of waste waters or to reduce deforestation and erosion, the huge challenge of the reduction of cyanobacterial blooms in LV by the control of eutrophication seems far from being achieved.

Benefits of Adding Virginiamycin to Arapaima gigas (Schinz, 1822) Diet Cultivated in the Brazilian Amazon

The aim of this study was to evaluate the physiological, zootechnical, and environmental benefits of the use of growth-promoting virginiamycin in the pirarucu diet. The research was conducted at the Carlos Eduardo Matiazze Fish Center, Federal University of Rondônia. In this study, 96 pirarucu fish were distributed in excavated nursery, divided into two treatment groups, control (0.0 mg kg^-1) and treatment (75.0 mg kg^-1) of feed with virginiamycin, with 8 replications in a completely randomized design. With virginiamycin being incorporated into commercial feed, for 107 days of cultivation, the fish were slaughtered with an average weight of 9.18 kg. Carcass weight, flesh, residues, and internal organs/guts were evaluated to calculate slaughter yields, Spearman's correlation, and subsequently regression. For the quantification of micronuclei, a count of 1,000 cells per blade was determined. The means of the results obtained were contrasted by the Student's t-test (α = 0.05). Virginiamycin did not cause oscillations in the limnological variables of the nursery but could reduce micronucleated erythrocytes. The average yields in carcass, flesh, and waste were 67.43, 53.4, and 43.14%, respectively. Virginiamycin provided strong correlations (ρ ²) for better productive yields and lower slaughter residue. The hepatosomatic index indicated a strong relationship between liver weight and fat. Virginiamycin may be recommended for fish farming in pirarucu fattening because it contributes to the productive efficiency and sustainability of the fish farm system.

Fish Husbandry Practices and Water Quality in Central Kenya: Potential Risk Factors for Fish Mortality and Infectious Diseases

Fish mortality has an enormous impact on the aquaculture industry by reducing fish production and slowing industrial growth. A cross-sectional study was carried out in Kirinyaga County, Central Kenya, to evaluate potential risks of fish mortality and disease transmission and suitability of pond water for rearing fish. A semistructured questionnaire that focused on general information, management practices, and disease history was administered to 92 small-scale fish farmers. Parasitological examination of fish sampled from selected farms (farms that were reporting mortality at the time of sampling) was done by following the standard procedure. Water quality parameters for 33 ponds were evaluated in situ (recorded on pond site) and ex situ (analysed at the laboratory) following the standard methods. The risks were assessed by adjusted odds ratio based on univariate regression analysis. Prevalent fish husbandry practices that were found to be associated with fish mortality and acquisition of pathogens in the study area were the use of raw livestock manure (0R = 1.500), high fish stocking density (0R = 1.168), and feeding fish on homemade rations (0R = 1.128). Parasitological investigation found infestation with Diplostomum spp., Dactylogyrus spp., Clinostomum spp., and Piscicola leeches. Water temperature and pH were found fit for rearing fish. Of the 33 fishpond water samples tested, 1 (3%) and 6 (18%) exceeded the recommended limits of <100 mg/L and <0.2 mg/L of nitrate and nitrite, respectively. Of the 29 fishpond water tested, 15 (59%) exceeded the recommended limits of <100 mg/L of total ammonia. The findings show that the use of raw livestock manure, high fish stocking density, high nitrates and nitrites, and high ammonia levels in fishponds are potential risk factors for fish mortality and acquisition of infectious pathogens in a pond environment in a rural setup, in Central Kenya. There is a need to address the above factors in small-scale farming practices to minimize fish loss and also to prevent the occurrence and spread of infectious pathogens.

Growth, production and feed conversion performance of the gurami sago (Osphronemus goramy Lacepède, 1801) strain in different aquaculture systems

Background: Giant gourami ( Osphronemus goramy, Osphronemidae), belonging to gurami sago strain, is an important economic fish species that was newly released for domestication in 2018 in Indonesia. The present study aimed to determine the growth, production and feed conversion efficiency of gurami sago strain in different aquaculture systems.

Methods: A mean of 240 juveniles were stocked (initial weight mean, 54.53 g and length 13.88 cm) into concrete ponds, floating net cages and earthen freshwater ponds (12 m ³) with three replicates of each. The juveniles were fed a floating commercial pellet diet containing 30% crude protein and 5% crude lipids. Feed was supplied at 3% of fish biomass per day throughout the 90 days of the experiment. The research was conducted in the area surrounding Lake Maninjau of Indonesia.

Results: After 90 days, the mean weight of fish reared in concrete ponds was 166.86 g, floating net cages was 179.51 g and earthen freshwater ponds was 149.89 g. The mean final biomass was 37.64 kg for concrete ponds, 41.27 kg for floating net cages, and 33.72 kg for earthen freshwater ponds. The specific growth rates (%/day) for concrete ponds, floating net cages and earthen freshwater ponds were 0.67, 0.75 and 0.62, respectively. The feed conversion rates were 1.45 for concrete ponds, 1.30 for floating net cages and 1.87 for earthen freshwater ponds. The net yields (kg m ^ˉ3) were 2.05 for concrete ponds, 2.27 for floating net cages, and 1.73 for earthen freshwater ponds. The exponents (b) of the length–weight relationship were calculated for concrete ponds (1.0146), floating net cages (1.2641), and earthen freshwater ponds (1.0056).

Conclusion: The study showed that the growth performance, production and feed conversion efficiency of the gurami sago strain were the best found in floating net cages and considered a new aquaculture system in the future.

Biodegradation of Sulfamethoxazole in Milkfish (Chanos chanos) Pond Sediments

To cope with bacterial infections, broad-spectrum antibiotics such as sulfonamides have been largely used for intensive coastal aquaculture. Sulfonamides are stable and difficult to remove by conventional wastewater treatment. Environmental pollution will occur if sulfonamide-containing aquaculture wastewater is discharged into rivers and oceans. In this study, high salinity-tolerant bacterial strains A12 and L with sulfamethoxazole (SMX)-degrading ability from milkfish (Chanos chanos) culture pond sediments with SMX were isolated, identified, and characterized. The degradation of SMX and the changes in the bacterial community in milkfish culture pond sediments were assessed. Phylogenetic analysis using 16S rRNA gene sequences suggested that bacterial strain A12 was very close (99% sequence identity) to Vibrio sp., and bacterial strain L was very close (99% sequence identity) to Pseudomonas sp. Aerobic and anaerobic batch and continuous SMX addition experiments indicated that bacterial strains A12 and L could enhance SMX degradation in milkfish culture pond sediments. Different microbial community compositions under aerobic and anaerobic conditions exhibited different SMX-degrading abilities. The results of this study suggest that bacterial strains A12 and L provide a solution for treatment of wastewater and sediment from SMX-contaminated high salinity milkfish culture ponds.

Improvements in the growth performance, immunity, disease resistance, and gut microbiota by the probiotic Rummeliibacillus stabekisii in Nile tilapia (Oreochromis niloticus)

The application of probiotics as an eco-friendly alternative to antibiotics is an emerging strategy for sustainable aquaculture. In the present study, Rummeliibacillus stabekisii was isolated from the gut of Nile tilapia, and the effects of R. stabekisii on the growth, innate immunity, disease resistance, and gut microbiota of Nile tilapia (Oreochromis niloticus) were investigated. The results showed significantly increased weight gain (WG), feed conversion ratio (FCR), and feed efficiency (FE) in Nile tilapia fed R. stabekisii for 8 weeks compared to those in fish fed a control diet. Intestinal digestive enzymes such as protease, cellulase, and xylanase were also significantly increased in the R. stabekisii-administered groups. Enhanced cumulative survival was exhibited in fish fed R. stabekisii after challenge with Aeromonas hydrophila and Streptococcus iniae. Immune parameters such as the phagocytic activity, respiratory bursts, and superoxide dismutase of head kidney leukocytes; serum lysozyme activity; and expression of the cytokine genes interleukin-1β, tumor necrosis factor-α, transforming growth factor-β, and heat shock protein 70 were significantly elevated in fish fed R. stabekisii. Administration of R. stabekisii considerably increased the abundance of potential probiotics (Bacillus and Lactobacillus spp.) and reduced abundances of potential pathogenic bacteria (Streptococcus and Staphylococcus spp.) in fish intestines. The present study indicated that dietary supplementation with R. stabekisii improved the growth, immunity, disease resistance, and gut microflora of Nile tilapia. This research is the first study reporting that the genus Rummeliibacillus is a potential probiotic in animals, suggesting that R. stabekisii can be used as a feed additive to enhance the growth and health status in tilapia.

Dietary administration of probiotics modulates non-specific immunity and gut microbiota of Nile tilapia (Oreochromis niloticus) cultured in low input ponds

Poor culture conditions in low input ponds make fish highly susceptible to infectious pathogens which lead to diseases and mortalities yet the effects of probiotics on immunity, gut microbiota and microbiological quality of fish in low input ponds are unknown. Nile tilapia, Oreochromis niloticus fingerlings (40 g) were randomly stocked at 50 fish m⁻³ in 1.25 m³ cages in low input ponds. The fish were fed on diets supplemented with either Saccharomyces cerevisiae (1 × 10¹⁰ CFU g⁻¹) or Bacillus subtilis (1 × 10⁹ CFU g⁻¹) at six levels: Diet 0 (No probiotic); S. cerevisiae at 2 g kg⁻¹ (Diet 1); 4 g kg⁻¹ (Diet 2) and 6 g kg⁻¹ (Diet 3) and B. subtilis at 5 g kg⁻¹ (Diet 4); 10 g kg⁻¹ (Diet 5) and 15 g kg⁻¹ (Diet 6) for 180 days. Results indicate that hemato-immunological parameters (hemoglobin (Hb), red blood cells (RBC), white blood cells (WBC) serum protein, albumin, globulin and lysozyme activity) were significantly higher in fish fed on probiotic treated diets compared to the control (P < 0.05). On the contrary, fish fed on Diet 6 presented significantly similar Hb and globulin values compared to the control (P > 0.05). Additionally, fish fed on probiotic treated diets retained the probiotics in their guts and lower microbial load was realized in their muscle (P < 0.05). In conclusion, B. subtilis and S. cerevisiae supplementation in diets of Nile tilapia reared in low input ponds improves immunity, manipulates gut microbiota and enhances fish flesh quality.

Growth and Nutrient Removal Efficiency of Sweet Wormwood (Artemisia annua) in a Recirculating Aquaculture System for Nile Tilapia (Oreochromis niloticus)

The maintenance of optimal water quality for fish production is one of the major challenges in aquaculture. Aquaponic systems can improve the quality of water for fish by removing the undesirable wastes and in turn produce a second marketable crop. However, there is no information on the growth and nutrient removal capability of Artemisia annua in aquaponic systems. This study evaluated the effect of plant density on water quality, the growth of A. annua and Oreochromis niloticus in a small scale aquaponic system in Kenya. The aquaponic system consisted of three treatments representing different plant densities (D1: 48 plants/m2, D2: 24 plants/m2 and D3:0 plants/m2). The high plant density system contributed significantly (p < 0.05) to the removal of all nutrients. The removal efficiency of ammonia was significantly higher in D1 (64.1 ± 14.7%) than in D2 (44.5 ± 6.8%) and D3 (38.0 ± 12.1%). Nitrates and nitrites were inconsistent, whereas phosphorus increased gradually in all treatments. The productivity of plants was higher in D1 than D2. Fish growth rates were significantly higher in D1 (0.35 ± 0.03 g/d) and D2 (0.32 ± 0.02 g/d) than in D3 (0.22 ± 0.04 g/d). The results show that A. annua can be cultivated in aquaponic systems due to its nitrogen removal capabilities.