Carnivorous Fish Species Research Articles

Response patterns of biomarkers in omnivorous and carnivorous fish species exposed to multicomponent metal (Cd, Cr, Cu, Ni, Pb and Zn) mixture. Part III.

Toxicity to fish of multicomponent metal mixtures at maximum-permissible-concentrations (MPC: Cd-0.005, Cr-0.01, Cu-0.01, Ni-0.01, Pb-0.005 and Zn-0.1 mg/L) set for EU inland waters was evaluated using the whole-mixture approach. An extended follow-up study on the biological effects of multicomponent metal mixtures on three ecologically different fish species, i.e. Perca fluviatilis, Rutilus rutilus, and Salmo salar is reported. The aim of this study was to assess response patterns of biomarkers (erythrocytic nuclear abnormalities (ENAs), metal accumulation and metallothioneins) in tissues of fish species after 14-day treatment with multicomponent metal mixtures at MPC and metal mixtures with one of its components at reduced MPC (↓). After treatments with Cu↓ and Cr↓, the lowest amount of Ni was found in all tissues (except the liver) of all fish species tested. After Zn↓ and Pb↓ treatments, the amount of Ni in muscle of all the tested fish species significantly decreased. The highest amounts of Cr in gills and Pb in muscle were detected in all fish species after treatments with Ni↓ and Cd↓ mixtures, respectively. R. rutilus accumulated significantly larger amounts of metals than P. fluviatilis and S. salar. The data obtained show that tissues of the omnivorous R. rutilus exposed to metal mixtures accumulated higher amounts of Cr, Cu, Ni and Zn, while tissues of carnivorous S. salar and P. fluviatilis higher amounts of Cd and Pb. The analysis of ENAs revealed concentration-dependent responses, indicating Cu↓ and Cr↓ treatments as causes of higher geno- and cytotoxicity levels.

Valorisation and enhanced sustainability of Senegalese sole (Solea senegalensis) aquaculture by dietary use of ditch shrimp (Palaemonetes varians) meal

The European Blue Growth Strategy requires innovative proposals contributing to sustainable development of the aquaculture activity. Within this context, ditch shrimp (Palaemonetes varians) meal obtained from extensively managed aquaculture wetlands was assessed as a potential source to substitute dietary fishmeal (FM) in compound diets for Senegalese sole (Solea senegalensis) juveniles. Estuarine ditch shrimp biomass from an integrated aquaculture system was converted into a meal that contained 61.9% protein and 9.2% lipid on a dry matter (DM) basis. The n-3 highly unsaturated fatty acids (HUFA) constituted the main fraction of the polyunsaturated fatty acids (PUFA). Three isonitrogenous (55% DM), isolipidic (12% DM) and isoenergetic (17 kJ g−1 DM) diets containing three substitution levels of FM by ditch shrimp meal (SM) were elaborated: 100% FM + 0% SM (SM0); 50% FM + 50% SM (SM50) and 0% FM + 100% SM (SM100). The experimental diets were tested on duplicate groups of sole juveniles (~4 g body weight) in an experiment that lasted 63 days. The substitution of dietary FM with SM did not influence growth and feed intake of the reared fish. Juveniles fed SM100 significantly decreased their muscle and skin lipid depositions in comparison with soles fed SM0. Moreover, muscle lipid analyses showed arachidonic acid (ARA) enrichment caused by the SM dietary use and a major presence of the n-3 over n-6 PUFA. Overall results demonstrate that dietary incorporation of P. varians meal in compound diets for Senegalese sole would add nutritional value to the harvested product with no impact on growth performance of reared fish. The dietary use of a low trophic level marine resource is an innovative practice that may contribute to a further sustainable development of aquaculture of carnivorous fish species.

Human health risk of methylmercury from fish consumption at the largest floodplain in Colombia

Colombia is one of the countries with the highest emissions of mercury (Hg) to the environment, due to its use in gold mining. This study evaluated the human health risk from exposure to Hg through fish consumption in 11 municipalities located in the Mojana region, northern Colombia. The study participants (n = 839) were categorized into three population groups: children (CHD), women of childbearing age (WCHA) and the rest of population (RP). Total Hg (THg) and methylmercury (MeHg) concentrations were evaluated in the top ten most consumed fish species (n = 292). Median concentrations (range: 0.22–0.58 μg/g ww) of the five carnivorous fish species exceeded the reference limit established by FAO/WHO (0.2 μg/g ww) for vulnerable populations. For 6 of the 10 studied fish species, the estimated weekly intake (EWI) in children was above the provisional tolerable weekly intake (PTWI, 1.6 μg/kg bw/week) of MeHg established by JECFA. EWI values for WCHA were above PTWI in 4 fish species, whereas in general, for RP group values were below PTWI (3.2 μg/kg bw/week). Our assessment of potential risks to MeHg exposure indicated that most of the consumed fish could generate negative effects in vulnerable groups, because according to ingestion rate, MeHg permissible is, in some cases, up to 4 times higher than reference limits. Consumption advisories should be a guidance to avoid risk, gain nutritional benefits, and sustain fish populations. Because its high MeHg levels as well as high ingestion, it is recommended that inhabitants of this region should stop eating certain kinds of fish and the whole fish as a single meal. To reduce its harmful intake, we have proposed a didactic strategy based on marbles that control the portion of fish they are eating.

Particular gene order and complete mitochondrial genome of Ariosoma meeki (Congridae, Ariosoma)

Ariosoma meeki (A. meeki) is a demersal and carnivorous fish species belongs to the family Congridae. Some wild populations of A. meeki are in danger because of the overfishing and environmental pollution. In order to better understand the germplasm resources, the complete mitochondrial genome of A. meeki was firstly determined in this study. The complete mitochondrial genome is 16,404 nucleotides, comprising 12 protein-coding genes, 2 ribosomal RNA genes, 20 tRNA genes, and 2 main non-coding regions, but ND6 and two tRNA genes were not found in the A. meeki mitogenome. The A. meeki mitogenome was currently the first member of Ariosoma genus with gene and tRNA deletion. In addition, phylogenetic analysis result demonstrated that A. meeki and A. shiroanago were clustered in a clade and formed a sister relationship.

Housefly (Musca domestica) Larvae Preparations after Removing the Hydrophobic Fraction Are Effective Alternatives to Fish Meal in Aquaculture Feed for Red Seabream (Pagrus major)

Insects are an attractive alternative to fish meal (FM) as a sustainable protein source in aquaculture feed that does not negatively impact the marine ecosystem. Despite housefly (Musca domestica) larvae having adequacy of amino acid profiles, they have sometimes been reported to be inferior to FM, especially for marine carnivorous fish species. Here, we report that the removal of the hydrophobic fractions from housefly larvae enables significant replacement of FM in the diet of the red seabream (Pagrus major). In a feeding trial, housefly (HF) larvae that had the hydrophobic fraction removed as a complete substitution for 70% FM produced satisfactory growth. However, HF larvae that were supplemented with the hydrophobic fraction resulted in significant growth reduction. Growth recovery was incomplete by supplementation of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) to undefatted HF larvae, being equivalent to that of fatty acid content with a control diet. Moreover, fish with a dietary intake of catechol identified from the hydrophobic fraction of the HF showed growth reduction and morphological alterations in the intestine. Our findings indicate that the hydrophobic fraction from HF larvae contains a negative factor for fish growth and eliminating the fraction from HF larvae is thought to be an important process for sustainable aquaculture.

Fish performance, nutrient digestibilities, and hepatic and intestinal morphologies in grouper Epinephelus fuscoguttatus fed fermented copra meal

Protein enhanced copra meal (PECM®) is an alternative, cheap, and sustainable source of plant protein for the aquafeed industry, albeit its use on carnivorous fish species has been very limited. A 70-day feeding trial using grouper Epinephelus fuscoguttatus (initial mean body weight of 1.86 ± 0.19 g) tested fermented copra meal as feed ingredient. Six isonitrogenous (crude protein of 45%) and iso-lipidic (crude fat of 11%) diets consisted of PECM®: a control diet at 0% soybean meal replacement (C); four diets replacing soybean meal at 25% (FC25), 50% (FC50), 75% (FC75), 100% (FC100) – all with methionine and lysine supplementation; and 100% soybean replacement without methionine and lysine supplementation (FCW100). Growth and feed performance were not significantly (P > 0.05) affected by PECM® replacement of soybean meal up to 100%, even without methionine and lysine supplementation. Chemical body composition was likewise not significantly (P > 0.05) altered. PECM® when used as a grouper feed ingredient has protein, lipid, carbohydrate and dry matter digestibilities of 89.28%, 78.63%, 82.57%, and 48%, respectively. Hepatic and intestinal morphologies displayed no apparent pathological changes. PECM® can be efficiently utilized by grouper and can replace soybean meal up to 100% (16% in diet) for normal fish performance and digestive organ functions.

Effects of calcium carbonate inclusion in low fishmeal diets on growth, gastrointestinal pH, digestive enzyme activity and gut bacterial community of European sea bass (Dicentrarchus labrax L.) juveniles

Fishmeal (FM) possesses one of the highest buffering capacities in comparison to most alternative vegetable aquafeed ingredients and its decreasing content in current formulations might affect the ideal gastrointestinal environment for digestive enzyme action and gut bacterial community of carnivorous fish species. A study was undertaken, therefore, to assess growth response, gastrointestinal pH, digestive enzyme activity and gut bacterial community of European sea bass (Dicentrarchus labrax L.) juveniles fed low FM diets (10% FM) with or without a feed buffering additive, calcium carbonate (FM10 + B and FM10, respectively) in comparison to a standard FM diet (20% FM, FM20). Three isonitrogenous and isolipidic extruded diets were fed to triplicate fish groups of 80 individuals (initial weight: 23 g) to overfeeding over 64 days. No significant differences due to low FM dietary levels were observed in final body weight, specific growth rate, feed intake, feed and protein efficiency. Low FM diet did not affect gastrointestinal pH in the stomach, anterior intestine, mid-intestine and hindgut at 0, 4, 8 and 12 hours post meal (hpm) while the inclusion of calcium carbonate in low FM diet seems to slightly increase the pH in the hindgut at 12 hpm. The absence of significant differences of pepsin, chymotrypsin, amylase and lipase activity suggests a comparable digestive efficiency among treatments although trypsin activity was slightly reduced in low FM diets after 4 hpm. Decreasing FM content seems to exert an effect on the overall gut bacterial community analysed by next-generation sequencing even if no significant effects on specific bacterial component were detected. The gut bacterial community in all the treatments was particularly rich in lactic acid bacteria such as Lactobacillus spp. which may provide important beneficial functions for the host and be associated with a healthy intestinal epithelium. According to the results, increasing the feed buffering capacity does not seem to improve digestive conditions while it is feasible to include 10% FM dietary level in practical formulation for European sea bass juveniles without negatively affecting growth, feed efficiency and digestive luminal conditions.

Effect of Dietary Carbohydrate-to-Protein Ratio on Gut Microbiota in Atlantic Salmon (Salmo salar).

Simple SummaryCarbohydrates, in the form of energy reserve polysaccharides, are major food components that supply low-cost energy in farm animal feed formulation. Most of these compounds are obtained from plant ingredients (i.e., cereal grains). As the aquaculture industry moves towards formulating marine-derived ingredients free diets, the inclusion of plant ingredients is expected to continuously increase, and thus the amount of carbohydrates in aquafeed formulation will increase as well. Carnivorous fish, including salmonids, show a slow blood glucose clearance rate and suboptimal growth performance when fed rich carbohydrate meals. The role of gut microbial communities on carbohydrate utilization has been poorly explored in salmonids. Hence, we conducted an experiment to evaluate the effect of feeding a high carbohydrate diet to Atlantic salmon (Salmo salar) on gut microbiota composition. Our results suggest increasing the level of digestible carbohydrate mostly affects low-abundance bacteria in favor of those capable of using carbohydrates as a major energy-yielding substrate. Further study for a better understanding of the role of gut microbiota in carbohydrate utilization in carnivorous fish is required.Atlantic salmon (Salmo salar) is a carnivorous fish species whose productive performance tends to be suboptimal when fed low-cost carbohydrate rich meals. It is of interest to study the dynamics of gut microbiota communities in salmonids fed high carbohydrate diets since gut microbes are referred to as key players that influence the metabolism and physiology of the host. A study was conducted to determine the effect of feeding a high carbohydrate diet to Atlantic salmon in gut microbiota communities. A medium carbohydrate (15% wheat starch)/medium protein (MC/MP) diet or a high carbohydrate (30% wheat starch)/low protein (HC/LP) diet was fed to triplicate tanks (28 fish each) during four weeks. We conducted an in-depth characterization of the distal intestine digesta microbiota using high-throughput sequencing of the V4 region of the 16S rRNA gene. Firmicutes, Actinobacteria and Proteobacteria were the major phyla determined in either experimental group. Phylum Planctomycetes, class Planctomycetia, order Planctomycetales and genus Lactococcus were significantly more abundant in fish fed the HC/LP diet compared with fish fed the MC/MP diet. Our study suggests feeding a carbohydrate rich meal to salmon exerts a low impact on the structure of gut microbial communities, affecting mostly low-abundance bacteria capable of metabolizing anaerobically carbohydrates as a major energy-yielding substrate.

Nutritional regulation of pyruvate kinase and phosphoenolpyruvate carboxykinase at the enzymatic and molecular levels in cobia Rachycentron canadum.

Despite being a carnivorous fish species, cobia (Rachycentron canadum) can utilize high levels of dietary carbohydrate (up to 360gkg-1). By contrast, rainbow trout (also carnivorous) cannot, due to the absence of molecular induction of glycolytic enzyme and inhibition of gluconeogenic enzyme gene expressions such as pyruvate kinase (PK) and phosphoenolpyruvate carboxykinase (PEPCK). We hypothesized that this phenomenon is species-specific and will not be observed in cobia. Our results show that, at the molecular level, the mRNA abundance of the important glycolytic (PK) and gluconeogenic (PEPCK) enzymes in cobia liver are regulated by dietary carbohydrate-to-lipid (CHO:L) ratios and nutritional status (fed, unfed, and refed). Significantly upregulated hepatic PK and depressed PEPCK gene expressions were observed when the fish were fed with an increasing CHO/L-ratio diet or were refed. However, in contrast to gene expression, there was no significant effect of dietary CHO/L ratios on PK enzyme activity. The decrease in PEPCK activity was significantly found between low CHO/L ratio and high CHO/L ratio diets, whereas the moderate CHO/L ratio group showed intermediate values. But PEPCK activity appeared to be independent of nutritional status. These results suggest that nutritional regulation is obvious, at least at the molecular level, in the key hepatic enzymes (PK and PEPCK) of the glucose metabolism pathway, in response to different dietary CHO/L ratios and to the transition from being starved to fed. Determining whether other key enzymes involved in hepatic glucose metabolism contribute to glucose tolerance in cobia is necessary for further investigation of this phenomenon at the enzymatic and molecular levels.

Effects of replacing fish oil with wheat germ oil on growth, fat deposition, serum biochemical indices and lipid metabolic enzyme of juvenile hybrid grouper (Epinephelus fuscoguttatus♀ × Epinephelus lanceolatus♂)

Fish oil was one of most important feed ingredients for carnivorous marine fish species, but the production might not cover all the necessary quantity for aquaculture. Meanwhile wheat germ oil could be a potential alternative for fish oil in aquatic feed. Hence, a 70 day feeding trial was conducted to investigate the effects of dietary fish oil replaced by wheat germ oil (WGO) on the growth, lipid and fatty acids deposition, and lipid metabolic enzymes activities of juvenile hybrid grouper (initial weight 55.31 ± 0.68 g), E. fuscoguttatus♀ × E. lanceolatus♂. Six isonitrogenous and isoenergetic experimental diets were formulated with 0%, 20%, 40%, 60%, 80% and 100% replacement of fish oil by WGO. Survival rate, weight gain rate, specific growth rate, and feed conversion ratio were similar among fish fed with different diets. Viserosomatic index and mesenteric fat ratio were significantly increased by dietary WGO. No significant differences were observed in the compositions of whole body, muscle and liver. C18: 3n-3 and C18:2n-6 contents in tissues were significantly increased, but EPA and DHA were significantly decreased by dietary WGO. No significant differences were found on the activities of hepatopancreas lipoprotein lipase, hepatic lipase and fatty acid synthase, while the activity of intestinal lipase was decreased. Total cholesterol, high density lipoprotein cholesterol, and low density lipoprotein cholesterol in plasma were not affected, but triglyceride was increased by dietary WGO. It can be concluded from the results that about 71.8% dietary fish oil can be replaced by WGO in diets with 50% crude protein and 12% crude lipid for subadult hybrid grouper, and fatty acids deposition and biosynthesis of this species was quite different from that of other fish species.

Effects of different dietary ratios of docosahexaenoic to eicosapentaenoic acid (DHA/EPA) on the growth, non-specific immune indices, tissue fatty acid compositions and expression of genes related to LC-PUFA biosynthesis in juvenile golden pompano Trachinotus ovatus

The n-3 long chain polyunsaturated fatty acid (n-3 LC-PUFA) such as docosahexaenoic and eicosapentaenoic acids (DHA and EPA) are essential fatty acids for marine carnivorous fish. Thus, the determination of optimal dietary DHA/EPA ratio is essential for the development of better feed formulation. In the present study, a marine carnivorous fish species, golden pompano (Trachinotus ovatus) juveniles were subjected to six isoproteic and isolipidic diets contained differential ratios of DHA/EPA (0.53, 0.81, 1.17, 1.48, 1.69, and 2.12) and a constant level of n-3 LC-PUFA (1.20% of the dry weight). After the 10-week feeding trial, fish fed the diet with DHA/EPA ratios of 1.17 and 1.48 achieved the best growth performance, with significantly higher weight gain (WG) and specific growth rate (SGR) than that fish fed the other diets (P < .05). At the DHA/EPA ratio of 1.48 group, non-specific immune indices, including the activities of lysozyme (LZM), catalase (CAT) and superoxide dismutase (SOD) in serum were significantly higher than those of other groups (P < .05). Fatty acid compositions of T. ovatus muscle, liver, eye and brain were significantly affected by the diets. The content of DHA and DHA/EPA in muscle, eye and brain both markedly increased with increasing dietary DHA/EPA ratios, and the concentration of DHA in brain was much higher than other tissues. Both the expression of elovl5-like and Δ6 fad in liver and the expression of elovl4-like and Δ6 fad in brain significantly increased with increasing dietary DHA/EPA ratios (P < .05). When subjecting the WG to the second-order polynomial regression analysis, the maximal growth was achieved at 1.40 of DHA/EPA ratio for the juvenile T. ovatus, which was thought as the recommended optimum requirement of dietary DHA/EPA ratio in the current study.

Distribution and Bioaccumulation Characteristics of Cadmium in Fish Species from the Longjiang River in the Guangxi Autonomous Region

Emergent cadmium pollution can cause water quality deterioration in rivers, which destroys the aquatic eco-environment and poses threats to human health. Fish species in these aquatic systems are prone to such pollution incidents and act as important indicators of the pollution level. Because cadmium enters the systematic circulation of fish and is non-biodegradable, the investigation of cadmium accumulation in fish bodies provides insights into the detrimental effects of cadmium pollution on the aquatic biological system. This research aims to validate the eco-environmental risks associated with emergent cadmium pollution incidents based on the investigation of the different tissues and organs of diverse fish species. The investigation was conducted six times along the Longjiang River using sampling methods during which all fish species were also classified and analyzed based on the water layer they reside in and their feeding habits. The results show that the cadmium concentration in the fish tissues is significantly higher in the former three investigations compared with that of the latter three analyses. For herbivorous, carnivorous, and omnivorous fish species, the cadmium concentration of their different tissues and organs follows the order:kidney > liver > gut > gill > egg > scale ≈ muscle. The cadmium concentration in the kidney is significantly higher (P<0.05) than that in any other organs of the fish species. This agrees with the fact that the kidney intensively metabolizes and accumulates heavy metals. The cadmium concentration in the same tissues or organs of the fish species living in different water layers follows the trend:demersal fish species > middle lower-layer species > middle upper-layer species. The sequence of the cadmium bioaccumulation factors in the muscles of different fish species is omnivore > carnivorous > herbivorous, that is, 8.32, 6.33, and 5.15, respectively, while the bioaccumulation factors in the muscles of the fish species in different water layers decrease in the following sequence:demersal fish species (8.18) > middle bottom-layer fish species (7.70) > middle upper-layer fish species (4.99). These experimental results indicate the biomagnification effects in heavy metal-polluted aquatic environments, where the bioaccumulation of heavy metals by fish is related to both the overall pollution level and local residential environment.

Feeding of juvenile cobia, Rachycentron canadum: Evaluation of practical feeds, comparison of commercial fishmeal replacers, and estimation of essential amino acid requirements

Three studies were conducted with juvenile cobia, Rachycentron canadum: (Study 1) a 10‐week feeding trial within floating net cages to test the nutritional efficacy of different dietary feeding regimes (trash‐fish control diet, a semimoist diet, an in‐house dry formulated diet, and a commercial cobia feed); (Study 2) a 10‐week feeding trial within an indoor water‐recirculating tank‐based system to test the nutritional efficiency of different potential dietary fishmeal replacers (poultry byproduct meal, soy protein concentrate, feather meal), a diet without taurine supplementation, and a commercial cobia feed; and (Study 3) estimation of the essential amino acid (EAA) requirements of cobia based on EAA whole‐body composition in fast‐growing cobia fed a trash‐fish‐based diet. Fish performance in terms of growth and feed efficiency was the greatest within the outdoor net‐cage feeding trial, with fish fed the control trash‐fish‐based diet exhibiting the best performance. Although fish growth was poorer within the indoor feeding trials, fish performance was similar for most diets, with apparent crude protein digestibility coefficients of over 75% being obtained in all experimental diets in both feeding trials. The estimated EAA requirements of cobia obtained during this study were similar to those reported for other similar marine carnivorous fish species.

Temporal variabilities of δ13C and δ15N in an ecosystem from the Central-East Gulf of California: estimating trophic relationships

The foodweb of El Tóbari Lagoon (central-east Gulf of California) was studied for four seasons through the carbon and nitrogen isotopic characterization of primary producers, invertebrates, fish, birds and potential food sources. The range of δ13C measured was much wider for potential food sources than for consumers. Many organisms presented enrichments of δ13C and δ15N values. There was a clear trend toward increasing δ13C and δ15N from base organisms to top-predators in the four seasons. The isotopic and percentage of contribution data confirmed that suspended particulate organic matter and phytoplankton are the main organic source supporting the foodweb. Our results also imply the occurrence of a nutrient transfer from zooplankton to some invertebrates and juvenile fishes. Consumers were composed in four trophic levels, with trophic level 2 occupied by zooplankton and filter-feeders and trophic level 4 occupied by carnivorous fish and most bird species. Carnivorous fish exhibited dietary similarities by a considerable sharing of resources, which could be related to the abundance of possible prey, between invertebrates and juvenile fishes. Crustaceans and fish represented the main food sources of birds, although some birds showed more dietary variation (marine and offshore prey).

Glucose and lipid metabolic adaptations during postprandial starvation of Japanese flounder Paralichthys olivaceus previously fed different levels of dietary carbohydrates

Exogenous glucose loading is generally used to assess the capacity of glucose utilization in carnivorous fish. Examining the use of endogenous glucose during fasting provides a new perspective on assessing glucose metabolism in fish. Japanese flounder Paralichthys olivaceus, a marine carnivorous fish species, were starved for 3, 9, 24, 48 h, and 3, 7, 14, 21, 28 days, respectively, after a 10-week feeding trial with 12% (C12: 49.49% crude protein, 9.65% crude lipid and gross energy of 18.98 kJ g−1) and 20% (C20: 49.99% crude protein, 9.75% crude lipid and gross energy of 19.11 kJ g−1) of dietary carbohydrates (alpha-starch and corn starch). After feeding trial, fish fed different diets showed similar specific growth rate (3.62 vs 3.61) (P > .05). During starvation period, compared with 3 h, plasma glucose and insulin concentration increased at 9 h in both groups. A similar trend was found for the glycogen content and the mRNA levels of genes involved in glycolysis and pentose phosphate pathway in liver. And the gluconeogenic genes mRNA levels significantly increased since 9 h in C12 and 24 h in C20 (P < .05). Subsequently, liver glycogen in C12 fell significantly on the 3 d compared with 48 h and was depleted on the 7 d (P < .05). It significantly decreased on the 7 d compared with 3 d and was minimized on the 14 d in C20 (P < .05). Plasma glucose peaked at 48 h and 7 d in both groups. As for lipid metabolism, high levels of plasma triglyceride, cholesterol concentration and lipogenetic genes mRNA levels were observed within 9 h. Compared with 3 h, liver lipid significantly decreased on the 14 d in both groups (P < .05). The mRNA levels of genes related to beta-oxidation and ketogenesis was enhanced in later stages in both groups. In addition, in C20, greater changes of mRNA levels of genes involved in gluconeogenesis and lipolysis in liver were observed. It was concluded that primary substrate of energy sources switched from glycogen to lipid occurring on the 3 d-7 d in C12 and 7 d-14 d in C20. Besides, high dietary carbohydrate (C20) feeding activated greater gluconeogenesis and lipolysis during starvation. These observations demonstrated glucose and lipid metabolic responses of Japanese flounder during starvation were influenced by previous feeding with different levels of dietary carbohydrates.

Dietary composition of black drum Pogonias cromis in a hypersaline estuary reflects water quality and prey availability.

The Baffin Bay estuary is a hypersaline system in the Gulf of Mexico that supports an important recreational and commercial fishery for black drum Pogonias cromis, a benthic predator. Seasonal measurements of water quality variables, benthic macrofauna densities and biomass, and determination of P. cromis food sources using stomach-content and stable-isotope analyses were carried out to determine how P. cromis food sources change with water quality and how this may affect P. cromis diet. Gut-content analysis indicated P. cromis selectively consumed bivalves Mulinia lateralis and Anomalocardia auberiana. Isotope compositions demonstrated that P. cromis relied on these benthic food resources produced in the Baffin Bay estuary year-round. Biomass and densities of these bivalves were influenced by changes in water quality variables, particularly salinity and dissolved oxygen. Thus, this paper demonstrates the relationship between water quality variables, benthic macrofauna, and their use as food resources by a carnivorous fish species, and emphasizes the need for integrated assessments when studying the effects of water quality on ecosystem function. Holistic approaches such as these can provide important information for management and conservation of fishery resources and can improve predictions of ecosystem response to climate variability.

Amino acid-specific δ15N trophic enrichment factors in fish fed with formulated diets varying in protein quantity and quality.

Compound‐specific isotope analysis (CSIA) of amino acids (AAs) in consumer tissues is a developing technique with wide‐ranging applications for identifying nitrogen (N) sources and estimating animal trophic level. Controlled experiments are essential for determining which dietary conditions influence variability in N stable isotopes (δ15N) trophic enrichment factors in bulk tissue (TEFbulk) and AAs (TEFAA). To date, however, studies have not independently evaluated the effect of protein quantity and quality (digestibility) on TEFs, complicating the application of AA‐δ15N values for estimating trophic levels. We conducted a 98‐d feeding experiment using five formulated isoenergetic feeds prepared with a high‐quality protein source to evaluate the effect of protein quantity and quality on TEFs of liver and muscle tissues of juvenile Pacific yellowtail (Seriola lalandi), a carnivorous fish species. We decreased protein digestibility using well‐established protocols that do not change AA profiles. Growth rates were higher in diets with higher protein content, and isotopic equilibrium was reached for both fish tissues and all treatments. Protein quantity and quality influenced isotope discrimination depending on tissue type and AA. In liver tissue, bulk TEFs showed a limited but significant relationship with protein quality, but did not differ with protein quantity or quality in muscle. None of the pre‐established source AAs (Lys, Met, Phe, and Gly) TEFs varied significantly with protein quantity or quality in liver tissue. However, in muscle tissue, TEFPhe increased significantly with protein content and decreased in response to reduced digestibility, indicating it may not serve as proxy for baseline isotopic values used to calculate trophic level. Among trophic AAs, TEFLeu decreased significantly with increasing protein quantity in liver tissue, while both Leu and Ile TEFs decreased with lower protein digestibility in muscle tissue. Our results indicate that CSIA‐AA in liver tissue provides more robust source and trophic AA‐δ15N values than in muscle.

The effect of water temperature on muscle cellularity and gill tissue of larval and juvenile Lophiosilurus alexandri, a Neotropical freshwater fish

The effect of temperature on muscle development and gill tissue were investigated in larval and juvenile of Lophiosilurus alexandri, a carnivorous Neotropical fish species. Larvae and juveniles were reared at temperatures of 23, 26, 29 and 32 °C for 15 and 35 days, respectively. The larvae were fed Artemia nauplii, while the juveniles received a formulated diet. In both stages, high temperatures resulted in increased fiber diameter of white muscle. Moreover, a pronounced effect of hypertrophy was observed in later stages of development. No alterations to minimum fiber diameter, and similar mosaic standards of muscle growth dynamics, were observed in larvae kept at 23–32 °C, suggesting that hyperplasia was not effected during early stages of development. Gills were analyzed by Degree of Tissue Change (DTC), which is based on the severity of lesions. Significant morphological changes were observed in gills when juveniles were kept at 32 °C, which was considered moderate tissue damage. Temperature modulates cellularity in L. alexandri larvae and juveniles, with pronounced alterations of hypertrophy of white muscle fibers in later stages of development when exposed to elevated temperatures. Higher temperatures may also induce muscle growth dynamics with increased recruitment of new white fiber, increased fiber diameter in the early stages and induced gill lesions.

Adaptation of Nile tilapia (Oreochromis niloticus) to different levels of dietary carbohydrates: New insights from a long term nutritional study

The objective of this study was to examine the long-term effects of different levels of dietary carbohydrates on glucose metabolism in the omnivorous Nile Tilapia (Oreochromis niloticus). Fish were fed from the first feeding stage until the adult stage, over a period of 40 weeks, using three different levels of carbohydrates (dextrin): 0% (CHO-L), 30% (CHO-M) and 50% (CHO-H). Growth performance, blood metabolite parameters, the proximate composition of the whole body, muscle and liver tissue, and the mRNA levels for genes involved in glycolysis, gluconeogenesis, lipogenesis and glucose transport in liver and muscle tissue were analyzed at week 26 and week 40. Fish fed the CHO-M diet exhibited the best growth performance, while the fish fed with the CHO-H diet showed the lowest growth performance. These data suggest that the incorporation of a certain level dietary carbohydrates can benefit Nile Tilapia. However, if the proportion of carbohydrates is very high, and concomitantly, the level of dietary proteins too low, this will not promote growth. Fish fed with carbohydrates exhibited a significant increase in lipid deposition in the whole body, muscle and liver tissues in. This seems to be due to increased lipogenic capacity, as reflected by higher hepatic fatty acid synthase mRNA levels and activity, as well as higher levels of plasma triglyceride. Nile Tilapia appear to be able to effectively adapt to the intake of carbohydrates, as reflected by: (i) the weak postprandial hyperglycemia (5.3–6.1 mM), (ii) the higher level of hepatic glycogen, (iii) the higher glycolytic pyruvate kinase enzyme in muscle (mRNA level and activity) and (iv) the inhibition of the gluconeogenic pathway for glucose-6-phosphatase and phosphoenolpyruvate carboxykinase enzymes (at molecular and enzymatic levels). Overall, these data show that the well-known differences in the capacity of carnivorous and omnivorous fish species to use dietary carbohydrates could be linked to differences in the regulation of the gluconeogenic and lipogenic pathways.

Natural food intake by juvenileArapaima gigasduring the grow-out phase in earthen ponds

In carnivorous fish species, zooplankton is one of the main food items in the early life stages and some fish species continue feeding on such food items further along the life stages even in the farming environment. In this study, the intake of natural food items was assessed in juvenile pirarucu Arapaima gigas reared in earthen ponds. Juvenile pirarucu (12.2 ± 4.32 g and 12.1 ± 1.13 cm) were stocked in fertilized earthen ponds (240 m²). For the analysis of the fish stomach content and plankton in the pond water, the fish and pond water were sampled weekly for 75 days and biweekly until the fish reached a mean weight of 750 g. Although artificial feed was used, pirarucu also ingested the natural food available in the pond water. Among the zooplankton, pirarucu demonstrated feeding preference for cladocerans despite the abundance of rotifers and copepods. Cladocerans were present in more than 80% of the stomach contents of fish up to 300 g and in 65%, 45% and 17% of fish of 301–500 g, 501–700 g and 701–900 g respectively. Copepods were present only in fish up to 500 g at low abundance. High ingestion of insects and plant material was observed in the stomach content of fish of all size classes. The results demonstrate that juvenile pirarucu ingest natural food available in the farming pond and suggests that the adoption of pond fertilization practices may have positive effects on fish growth performance.