Digestive enzyme activity of the Japanese grenadier anchovy Coilia nasus during spawning migration: influence of the migration distance and the water temperature

Hepatic immune response of Coilia nasus infected with Anisakidae during ovarian development

Anisakidae parasitism is a prevalent disease in wild populations of Coilia nasus, and can result in a significant loss of germplasm resources. To elucidate the immune response mechanism of C. nasus livers to Anisakidae infection, we collected and analysed 18 parasitic and 18 non-parasitic livers at gonadal developmental stages II, III, and V using histopathology, molecular biology and transcriptome methods. The hepatic portal area of the parasitic group exhibited an increase in the fibrous stroma and thickened hepatic arteries with positive Ly-6G staining, indicating inflammation and immune responses in the liver. Hepatocyte cytokine levels and the expression of liver function-related genes indicated that fish livers responded similarly to Anisakidae parasitism across different gonadal developmental stages. Oxidative stress indices showed more intense changes in stage II samples, whereas gene expression levels of Nrf2 and C3 were significantly increased in parasitised livers during stage III and V. Liver transcriptome sequencing identified 2575 differentially expressed genes between the parasitic and non-parasitic groups at the three gonadal developmental stages. KEGG pathway analysis showed that natural killer cell-mediated cytotoxicity, the NOD-like receptor signaling pathway, neutrophil extracellular trap formation, and other immune pathways were significantly enriched. Expression patterns varied across developmental stages, suggesting that innate immunity was primarily responsible for the liver immune response to Anisakidae infection during C. nasus migration, possibly related to water temperature changes or shifts in the gonadal developmental stage. In summary, this study investigated the immune response of C. nasus to Anisakidae parasitism under natural conditions, focusing on reproductive aspects and environmental changes, thereby establishing a foundation for elucidating the molecular mechanisms underlying the immune response of Anisakidae in C. nasus.

The application of protease in aquaculture: Prospects for enhancing the aquafeed industry

Low-fishmeal and protein-saving diets are two prominent nutritional strategies utilized to address challenges related to the scarcity and sustainability of protein sources in aquaculture. However, these diets have been associated with adverse effects on the growth performance, feed utilization, and disease resistance of aquatic animals. To mitigate these challenges, exogenous protease has been applied to enhance the quality of diets with lower protein contents or fishmeal alternatives, thereby improving the bioavailability of nutritional ingredients. Additionally, protease preparations were also used to enzymatically hydrolyze fishmeal alternatives, thus enhancing their nutritional utilization. The present review aims to consolidate recent research progress on the use of protease in aquaculture and conclude the benefits and limitations of its application, thereby providing a comprehensive understanding of the subject and identifying opportunities for future research.

A proteomics approach reveals digestive and nutritional responses to food intake in anadromous Coilia nasus

The estuarine tapertail anchovy, Coilia nasus, is an anadromous fish that undertakes over a 600-km spawning migration along the Yangtze River of China. They generally cease feeding during this process, but we recently documented that a small proportion of them appear to feed. Research on proteomic responses is essential for understanding the phenomenon of C. nasus feeding. In this study, we used an iTRAQ-based proteomics approach to study the changes in protein expression in response to food intake in C. nasus following voluntary fasting. Coilia nasus in the feeding group (CSI) were fed shrimp or small fish, whereas those in the control group (CSN) were starved. We identified 3279 proteins in the gastric tissue/stomach, of which 279 were significantly differentially expressed. In all, 133 differentially expressed proteins (DEPs) were upregulated and 146 proteins were downregulated in CSI compared with those in CSN C. nasus. In addition to gastric acid secretion caused by gastric distention, a functional analysis suggested that a series of DEPs were involved mainly in the regulation of protein digestion (e.g., carboxypeptidase A1 and chymotrypsin A-like), immune response (e.g., lysozyme and alpha 2-macroglobulin), and nutrition metabolism (e.g., glyceraldehyde 3-phosphate dehydrogenase, glycogenin, long-chain acyl-CoA synthetase, and creatine kinase). Real-time PCR confirmed that the mRNA levels of the DEPs were similar those obtained using iTRAQ. These results indicate that the nutrients obtained through food were effectively utilized by C. nasus, thereby providing energy for swimming, gonadal maturation, primary metabolism, and an enhanced immune function to better resist pathogen interference. This research contributes to the elucidation of nutritional regulation mechanisms of C. nasus to better protect the wild population.

Prejuveniles of Mugil liza (Actinopterygii; Fam. Mugilidae) show digestive and metabolic flexibility upon different postprandial times and refeeding

Many animals face periods of feeding restrictions implying fasting and refeeding. The determination of digestive/metabolic and body condition parameters at different times of food deprivation and after refeeding allows to evaluate the postprandial dynamics, the transition from feeding to fasting and the capacity to reverse digestive and metabolic alterations. In spite of its physiological importance, studies on estuarine-dependent detritivore fish are lacking. We determined total mass (TM), relative intestine length (RIL), hepatosomatic index (HSI), digestive enzymes activities in the intestine and energy reserves in liver and muscle at 0, 24, 72, 144 and 240 h after feeding and at 72 h after refeeding in prejuveniles of Mugil liza (Mugilidae) as a model species. After feeding, a decrease occurred in: TM (144 h, 25%), RIL (144 h, 23%); amylase and maltase (72 h, 45 and 35%), sucrase (24 h, 40%) and lipase (24 h, 70%) in intestine; glycogen and free glucose (72 h, 90 and 92%) in liver. In muscle, glycogen (72-144 h) and free glucose (144 h) (170% and 165%, respectively) peak increased; triglycerides decreased at 24-240 h (50%). After refeeding TM, RIL, carbohydrases activities in intestine, glycogen and free glucose in liver were recovered. In muscle, glycogen and free glucose were similar to 0 h; lipase activity and triglycerides were not recovered. Trypsin and APN in intestine, triglycerides in liver, protein in liver and muscle and HSI did not change. The differential modulation of key components of carbohydrates and lipid metabolism after feeding/refeeding would allow to face fasting and recover body condition. Our results improve lacking knowledge about digestive and metabolic physiology of detritivore fish.

Anisakidae parasitism activated immune response and induced liver fibrosis in wild anadromous Coilia nasus

Anisakidae nematode larvae is one of the most common parasites in wild anadromous Coilia nasus. This study aims to explore the mechanism of the C. nasus immune response to the parasitism of Anisakid nematode larvae. Results found that Anisakid nematode larvae parasitism caused liver injury as evidenced by histomorphology results as well as high levels of aminotransferase and aspertate aminotransferase. Furthermore, Anisakid nematode larvae parasitism induced an immune response in the host, which was characterized by the elevated populations of macrophages and neutrophils in the liver and head-kidney in the Anisakidae-infected group compared to the noninfected group. The expression of immunoglobulin IgM and IgD in the liver and head-kidney was also increased in the Anisakidae-infected group. The Anisakidae-infected group showed higher activity of antioxidant enzymes catalase and superoxide dismutase, which indicates severe oxidative stress, and increased production of pro-inflammatory cytokines, TNF-α, IL-6 as well as MCP-1 in the liver compared with the noninfected group. As a result of inflammation, livers of hosts in the Anisakidae-infected group showed fibrosis, and elevated expression of associated proteins including α-smooth muscle actin, fibronectin, collagen type I and type III compared with the noninfected group. We demonstrated that Anisakid nematode larvae parasitism results in injury and fibrosis in the liver, and triggers immune cell infiltration and inflammation in the liver and head-kidney of C. nasus. Altogether, the results provide a foundation for building an interaction between parasite and host, and will contribute to C. nasus population and fishery resource protection.

Understanding the early ontogenetic stages of Mugil liza (Mugilidae): Morphological traits and digestive/metabolic profile of pre-juveniles after recruitment

The family Mugilidae consists mainly of diadromous species, whose reproduction occurs in offshore waters. Pre-juveniles shift their diet in the surf zone (zooplanktophagous to iliophagous). Later, during their recruitment into estuaries, huge changes take place in their digestive system. However, digestive and metabolic characteristics and some morphological traits at recruitment are unknown for Mugilidae. We performed comparative studies on early and late pre-juveniles of Mugil liza recruited in Mar Chiquita Coastal Lagoon (37°32'-37°45'S, 57°19'-57°26'W, Argentina). We determined digestive enzyme activities (intestine), energy reserves (liver/muscle), total/standard length, total weight, intestinal coefficient, hepatosomatic index and retroperitoneal fat. Pre-juveniles exhibited amylase, maltase, sucrase, lipase, trypsin and aminopeptidase-N (APN) activities, which were maintained over a wide range of pH and temperature, and exhibited Michaelis-Menten kinetics. In late pre-juveniles, amylase (422 ± 131 μmol maltose min^-1 mgprot^-1 ), sucrase (86 ± 14 mg glucose min^-1 mgprot^-1 ), trypsin (84 ± 9 μmoles min^-1 mgprot^-1 ) and APN (0.58 ± 0.08 μmoles min^-1 mgprot^-1 ) activities were higher (42%, 28%, 35% and 28%, respectively) than in the early stage. Also, the intestinal coefficient was higher in late (3.04) compared to early (2.06) pre-juveniles. Moreover, the liver appeared to be a main site of glycogen and triglyceride storage in late pre-juveniles, muscle being the site of storage in early pre-juveniles, exhibiting higher glycogen, free glucose and protein concentrations (92%, 82%, 32%, respectively). The results suggest that pre-juveniles of M. liza exhibit an adequate digestive battery to perform complete hydrolysis of various dietary substrates, availability of energy reserves and morphological characteristics to support their feeding habit and growth after recruitment. Our results represent an important contribution to knowledge of the ecology and digestive physiology of pre-juveniles of Mugilidae in the wild.

Variations and Potential Factors of Gut Prokaryotic Microbiome During Spawning Migration in Coilia nasus

Coilia nasus is influenced by various external pressures during spawning migration and these anadromous transitions can lead to specific gut microbiome characteristics that affecting the host biological process. Therefore, the purpose of this study was to determine the variations of components and functions in the gut prokaryotic microbiome during spawning migration as well as the key factors that triggered the changes. The gut microbiome in C. nasus was mainly consisted of Proteobacteria, Bacteroidetes, Firmicutes, Deinococcus-Thermus and Fusobacteria via 16S rRNA Gene Amplicon Sequencing. The relative abundance of Acinetobacter and Clostridium increased, while Corynebacterium, Actinomyces, Bacillus, Klebsiella and Ochrobactrum decreased after entering freshwater, indicated the preference of C. nasus gut microbial members transferred from seawater to freshwater. Additionally, the proportion of Firmicutes significantly decreased and then increased, as well as the arise of some soil bacteria in gut, corresponding to the phenomenon that C. nasus are fasting during the upstream process and refeeding after entering the spawning grounds. The function prediction of gut microbiome was also consistent with the above results. The present study generally demonstrated the gut microbiome dynamics and the significant correlation between the gut microbiome and salinity and feeding behavior in the spawning migration of C. nasus.

Metabolic mechanisms of Coilia nasus in the natural food intake state during migration

As a prominent member of freshwater and coastal fish faunas, Coilia nasus migrates annually from the sea up the Yangtze River in China to spawn. It is traditionally believed that C. nasus generally do not feed during their spawning migration. However, we recently documented the occurrence of food intake phenomenon in C. nasus following voluntary fasting. The purpose of the current study is to explore the metabolic mechanisms on C. nasus in response to food intake during migration. A total of 23,159 differentially expressed mRNA molecules and 204 metabolites were identified in transcriptome and metabolome analyses. Our results provide insights into the activation of energy consumption and reinforcement of energy storage during migration, and also identify key genes involved in food intake regulation. Our findings will be useful for future research on population recruitment and energy utilization in wild C. nasus.

Effects of temperature on feeding and digestive processes in fish

As most fish are ectotherms, their physiology is strongly affected by temperature. Temperature affects their metabolic rate and thus their energy balance and behavior, including locomotor and feeding behavior. Temperature influences the ability/desire of the fish to obtain food, and how they process food through digestion, absorb nutrients within the gastrointestinal tract, and store excess energy. As fish display a large variability in habitats, feeding habits, and anatomical and physiological features, the effects of temperature are complex and species-specific. The effects of temperature depend on the timing, intensity, and duration of exposure as well as the speed at which temperature changes occur. Whereas acute short-term variations of temperature might have drastic, often detrimental, effects on fish physiology, long-term gradual variations might lead to acclimation, e.g. variations in metabolic and digestive enzyme profiles. The goal of this review is to summarize our current knowledge on the effects of temperature on energy homeostasis, with specific focus on metabolism, feeding, digestion, and how fish are often able to "adapt" to changing environments through phenotypic and physiological changes.