First detection and isolation of infectious haematopoietic necrosis virus from farmed rainbow trout in Nyeri County, Kenya

Management Practices, Farmers' Knowledge of Diseased Fish, and Their Occurrence in Fish Farms in Nyeri County, Kenya

In this study, fish farmers' management practices, occurrence, and knowledge of fish diseases in Nyeri County, Kenya, were evaluated. Fish farming management practices for small-scale farmers in Kenya have numerous challenges which have led to disease occurrence and reduced production. Moreover, the impact and association of these challenges to farmers' knowledge of fish diseases and their burden has not been fully studied. A semistructured questionnaire was used to capture farmers' biodata, fish species farmed, and farmers' management practices such as handling of nets, pond fertilization, and disposal of fish waste. Farmers' knowledge of fish diseases was based on their ability to identify independent and dependent variable indicators. Independent variables included clinical signs, decreased feeding, bulging eyes, floating on water, abdominal swelling, bulging eyes, abnormal skin color, reduced growth, and abnormal swimming with fish death as were the dependent variable. A total of 208 farmers were interviewed and included those of tilapia (134), mixed tilapia and catfish (40), catfish (22), rainbow trout, and five dams under cooperative management. Tilapia was the most kept fish species (66.8%) followed by polyculture of tilapia and catfish (20%) and rainbow trout (2%). Most respondents were male (78.5%) over 51 years of age (50%). Fifty percent of the respondents had secondary school education. There was a significant association between deaths and sharing of nets in Kieni East subcounty (p=0.0049, chi-square), while on-farm fish waste disposing appeared to cause higher deaths compared to burning of the waste although not statistically significant (p=0.13). Few respondents observed decreased feed uptake (<20%) and poor growth. Fifty-seven percent of farmers reported mortalities. Fish poor growth, floating in water, and management practices in subcounties had significant effect on fish deaths. The farmers had knowledge of signs of diseased fish, but there was paucity of knowing the specific causes of disease. Farmers need to be empowered on best aquaculture husbandry to avoid disease transmission and specific fish disease signs to enhance proper reporting of disease for subsequent mitigation measures.

First detection of infectious haematopoietic necrosis virus in farmed rainbow trout in North Macedonia

Infectious haematopoietic necrosis virus (IHNV) is the causative agent of infectious haematopoietic necrosis (IHN), a disease of salmonids responsible for great economic losses. The disease occurs in most parts of the world where rainbow trout is reared but has not been previously reported in North Macedonia. In this study, 150 pooled samples in total, each consisting of organ mix of 10 freshly killed rainbow trout Oncorhynchus mykiss, were collected from 50 trout farms by the Food and Veterinary Agency of North Macedonia as part of the annual surveillance plan for IHN and viral haemorrhagic septicaemia (VHS) control. Screening of samples was done by cell culture and real-time RT-PCR (qRT-PCR). All 150 tested samples were VHS virus (VHSV) qRT-PCR negative. Two samples from different trout farms were IHNV qRT-PCR positive. On cell culture, 1 IHNV qRT-PCR positive sample caused cytopathic effect after 2 passages on EPC cells. The virus, isolated from an asymptomatic rainbow trout fry, was identified by qRT-PCR and designated as MAKIHNV1. The phylogenetic reconstruction indicates that the isolated virus belongs to the European E genogroup, more specifically within the E-1 clade, and is similar to the German, Italian and Iranian isolates. This study has revealed for the first time the presence of IHNV in rainbow trout in North Macedonia. However, it is not possible to make interpretations about the source of infection from the phylogenetic analysis, and the origin of MAKIHNV1 remains unclear.

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.