Biochemical parameters as a measure of food availability and growth in immature rainbow trout (Oncorhynchus mykiss)

Pikeperch muscle tissues: a comparative study of structure, enzymes, genes, and proteins in wild and farmed fish

Pikeperch (Sander lucioperca) is a freshwater species and an internationally highly demanded fish in aquaculture. Despite intensive research efforts on this species, fundamental knowledge of skeletal muscle biology and structural characteristics is missing. Therefore, we conducted a comprehensive analysis of skeletal muscle parameters in adult pikeperch from two different origins, wild-caught specimens from a lake and those reared in a recirculating aquaculture system. The analyses comprised the biochemical characteristics (nucleic acid, protein content), enzyme activities (creatine kinase, lactate dehydrogenase, NADP-dependent isocitrate dehydrogenase), muscle-specific gene and protein expression (related to myofibre formation, regeneration and permanent growth, muscle structure), and muscle fibre structure. The findings reveal distinct differences between the skeletal muscle of wild and farmed pikeperch. Specifically, nucleic acid content, enzyme activity, and protein expression varied significantly. The higher enzyme activity observed in wild pikeperch suggests greater metabolically activity in their muscles. Conversely, farmed pikeperch indicated a potential for pronounced muscle growth. As the data on pikeperch skeletal muscle characteristics is sparse, the purpose of our study is to gain fundamental insights into the characteristics of adult pikeperch muscle. The presented data serve as a foundation for further research on percids' muscle biology and have the potential to contribute to advancements and adaptations in aquaculture practices.

Effect of Temperature Fluctuation and Nutritional Status on Starry Flounder, Platichthys stellatus, Survival and Adaptive Physiological Response

Starry flounder (Platichthys stellatus) is a commercially important cold-water fish. Our aim was to investigate the effects of fluctuating water temperature on flounders after periods of starvation and feeding. Fish were divided into starvation and feeding groups. The water temperature was increased stepwise in experiment 1; more focused variations, based on the results of experiment 1, were studied in experiment 2. At temperatures ≤27 °C, there was no significant difference observed in survival. At 28 °C, mortality increased, survival was lower (21%) in the starvation group than in the feeding group (46%), and weight loss was the highest (15%) in the starvation group. In experiment 2, survival was ≥86%, and there was no significant difference between the starvation/feeding groups. However, when the water temperature was increased to 27 °C after being decreased to 12 °C, weight loss was the highest (11%). Glucose, cortisol, superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH) levels increased with increasing water temperature, and then gradually decreased. Glutamic pyruvic transaminase (GPT)/glutamic oxaloacetic transaminase (GOT) levels showed large variations among individuals. Triglyceride, cholesterol, and protein levels gradually decreased with long-term starvation. Survival was not affected by water temperature drop ≤27 °C after starvation/feeding. These results indicate that 27 °C is the upper limit of tolerable water temperature for the survival of starry flounders. Therefore, aquaculture farms should ensure maintaining water temperatures at ≤27 °C during high-temperature periods.

Estimating volumes from common carp hepatocytes using design-based stereology and examining correlations with profile areas: Revisiting a nutritional assay and unveiling guidelines to microscopists

Assessing fish liver status is common in aquaculture nutrition assays. This often implies determining hepatocytes profile areas in routine thin (5-7 μm) histological sections. However, there are theoretical problems using planar morphometry in thin sections: inherent sampling cells biases, too small numbers of sampled cells, under/overestimation of size, measuring size as areas when cells are three-dimensional (3D) entities. The gold standard for assessing/validate cell size is stereology using thick sections (20-40 μm). Here, we estimated the volume of hepatocytes and their nuclei by the nucleator and optical disector stereological probes (in thick sections), and, innovatively, in thin sections too (using single-section disectors). The liver of common carp eating feed containing either low or high level of lipids was targeted. Results were compared with prior profile areas from planar morphometry using thin sections, and with profile areas estimated here with the two-dimensional (2D) nucleator. Ratios between nucleus and cell/cytoplasm (N/C) areas and volumes were calculated and compared. There was high positive correlation between volumes in thin and thick sections (r = .85 to .89; p < .001), empirically validating the single-section disector. Strong correlations existed between profile-derived versus 2D-nucleator areas (r = .74 to .83; p < .001). There was systematic underestimation of cells and nucleus size using planar morphometry. The N/C ratios derived from the 2D-nucleator data were higher than those from planar morphometry. Despite theoretical premises for using simple planar morphometry in thin sections are flawed, our results support that such morphometry on carp/fish hepatocytes may offer some valid biological conclusions. Anyway, we advanced guidelines for implementing proper methods.

Soya Saponins Induce Enteritis in Atlantic Salmon (Salmo salar L.)

Soybean meal-induced enteritis (SBMIE) is a well-described condition in the distal intestine of salmonids, and saponins have been implicated as the causal agent. However, the question remains whether saponins alone cause SBMIE. Moreover, the dose-response relationship has not been described. In a 10 week feeding trial with Atlantic salmon, a highly purified (95%) soya saponin preparation was supplemented (0, 2, 4, 6, or 10 g/kg) to two basal diets, one containing fishmeal as the major protein source (FM) and the other 25% lupin meal (LP). Saponins caused dose-dependent increases in the severity of inflammation independent of the basal diet, with concomitant alterations in digestive functions and immunological marker expression. Thus, saponins induced inflammation whether the diet contained other legume components or not. However, responses were often the same or stronger in fish fed the corresponding saponin-supplemented LP diets despite lower saponin exposure, suggesting potentiation by other legume component(s).

Long-term fasting in the anadromous Arctic charr is associated with down-regulation of metabolic enzyme activity and up-regulation of leptin A1 and SOCS expression in the liver

The life-strategy of the anadromous Arctic charr (Salvelinus alpinus) includes several months of voluntary fasting during overwintering in fresh water leading to emaciation prior to seawater migration in spring. In this study we compared changes in condition, substrate utilization and liver metabolism between captive anadromous charr subjected to food-deprivation during late winter and spring, and conspecifics fed in excess. In March, 9 out of the 10 sampled fed fish had not eaten, indicating that they were a voluntary anorexic state. In June, the fed fish were eating and all had higher body mass (BM), condition factor (CF) and adiposity than in March. In fasted fish there were only small decreases in BM, CF and adiposity between March and May, but all these parameters decreased markedly from May to June. The fasted fish were fat- and glycogen-depleted in June, had suppressed activity of hepatic enzymes involved in lipid metabolism (G6PDH and HOAD) and seemed to rely on protein-derived glucose as a major energy source. This was associated with up-regulated liver gene expression of leptin A1, leptin A2, SOCS1, SOCS2 and SOCS3, and reduced IGF-I expression. In an in vitro study with liver slices it was shown that recombinant rainbow trout leptin stimulated SOCS1 and SOCS3 expression, but not SOCS2, IGF-I or genes of enzymes involved in lipid (G6PDH) and amino acid (AspAT) metabolism. It is concluded that liver leptin interacts with SOCS in a paracrine fashion to suppress lipolytic pathways and depress metabolism when fat stores are depleted.

The metabolic effects of feeding and fasting in beluga Huso huso

A six week-study was conducted to determine the effect of starvation and feeding on growth, hematology and biochemical variables in sub-yearling beluga. Fish were placed on six feeding strategies: i) starved condition for 6 weeks, ii) a 2-week starvation, 2-week feeding and 2-week starvation, iii) a 2-week feeding, 2-week starvation and 2-week feeding, iv) a 3-week starvation followed by a 3-week feeding, v) a 3-week feeding with following 3-week starvation, and vi) fed throughout the 6 weeks. After 6 weeks, hematology, triacylglycerol, cholesterol, total protein, HSI, VSI, crude fat in muscle, final weight, feed conversion, specific growth rate, and condition factor were significantly affected by feeding strategies. The results suggested that most of the growth and physiological variables responded to a short period of starvation or re-feeding. These findings indicated that beluga could partially recover in weight and some physiological indices from periods of starvation when provided subsequently ad libitum feeding.

Physiological responses of dietary tryptophan fed Labeo rohita to temperature and salinity stress

Two experiments were conducted to elucidate the possible effects of dietary L-tryptophan (TRP) in Labeo rohita based on growth performance and physio-biochemical responses. In the experiment I, a 60-day feeding trial was carried out to elucidate the effects of dietary TRP enrichment on growth performance and physio-biochemical responses. In the experiment II, the TRP pre-fed L. rohita, from experiment I, was exposed to temperature and salinity stress to evaluate stress-mitigating efficacy of TRP. In L. rohita, dietary supplementation of TRP showed significant effect on weight gain percentage and feed conversion ratio but not on blood glucose. A significant increase in RNA content and RNA/DNA ratio upon TRP supplementation was observed and was positively correlated with growth performance. The results of experiment II indicated that weight gain percentage, serum T3 and T4 levels were significantly reduced in groups that were exposed to temperature and salinity stress and fed diets without TRP supplementation. However, dietary supplementation of TRP significantly augmented weight gain percentage in stress-exposed groups. Tryptophan supplementation helped in bringing back T3 and T4 levels comparable with control. A significant increase in superoxide dismutase, catalase, Adenosine triphosphatase, blood glucose and serum cortisol was observed in temperature- and salinity-exposed groups fed without TRP-supplemented diets. However, TRP supplementation was found to be effective in restoring the above parameters. The results of these experiments suggest that dietary TRP supplementation augments growth, lowers energy demand and helps in mitigating thermal and salinity stress in L. rohita.

Physiological responses to starvation in the European eel (Anguilla anguilla): effects on haematological, biochemical, non-specific immune parameters and skin structures

The physiological effects of short-term starvation on some haematological, biochemical and non-specific immune response parameters together with the histological structure of the skin, were investigated in the European eel, Anguilla anguilla. Blood haemoglobin and haematocrit, serum glucose and cortisol, hemolysins, haemagglutinins, and lysozyme in the plasma, kidney and epidermal extract, were measured in fish after 31, 42 and 58 days of starvation, and compared to those of fed fish. Starvation did not affect haemoglobin and haematocrit values, while an increase in glucose and cortisol levels was found in starved eels by day 42. Haemolytic and haemagglutinating activities decreased in starved eels. On the other hand, starvation caused an increase in the lysozyme content in the epidermal extracts, while no significant variations were observed in kidney and plasma. On the whole, no major changes in metabolic, haematological and non-specific immune parameters were observed when short-term (less than 2 months) starvation was applied to the European eel, suggesting an adaptive response to starvation, rather than a typical alarm-stress response, allowing this species to withstand food deprivation.

Influence of fasting on muscle composition and antioxidant defenses of market-size Sparus macrocephalus

The study was conducted to investigate fasting effects on flesh composition and antioxidant defenses of market-size Sparus macrocephalus. Two hundred fish (main initial weight 580 g) were divided into two groups (control and fasted) and reared in 6 cages. After two weeks of adaptation, group I fasted for 28 d; group II was fed normally as a control. In 3, 7, 14, 21 and 28 d, 6 fish per group were sampled for proximate flesh composition, liver antioxidant enzyme activities and malondialdehyde flesh content analyses. In fasted fish, the reduction of lipid content in muscle occurred after day 3, and, compared to controls, the content of protein decreased from day 14, the activities of liver antioxidative enzymes superoxide dismutase (SOD) and glutathione peroxidase (GPX) increased from day 3, and flesh malondialdehyde levels increased from day 21. Flesh fat reduction shows that fasting may be used as a technique to reduce flesh lipid content in Sparus macrocephalus. However, considering flesh protein loss and the subsequent oxidative stress, the fasting technique should be used with precautions.

Effect of diet composition and ration size on key enzyme activities of glycolysis–gluconeogenesis, the pentose phosphate pathway and amino acid metabolism in liver of gilthead sea bream (Sparus aurata)

The effects of diet composition and ration size on the activities of key enzymes involved in intermediary metabolism were studied in the liver of gilthead sea bream (Sparus aurata). High-carbohydrate, low-protein diets stimulated 6-phosphofructo 1-kinase (EC 2.7.1.11), pyruvate kinase (EC 2.7.1.40), glucose-6-phosphate dehydrogenase (EC 1.1.1.49) and 6-phosphogluconate dehydrogenase (EC 1.1.1.44) enzyme activities, while they decreased alanine aminotransferase (EC 2.6.1.2) activity. A high degree of correlation was found between food ration size and the activity of the enzymes 6-phosphofructo 1-kinase, pyruvate kinase, glucose-6-phosphate dehydrogenase (positive correlations) and fructose-1,6-bisphosphatase (EC 3.1.3.11) (negative correlation). These correlations matched well with the high correlation also found between ration size and growth rate in starved fish refed for 22 d. Limited feeding (5 g/kg body weight) for 22 d decreased the activities of the key enzymes for glycolysis and lipogenesis, and alanine aminotransferase activity. The findings presented here indicate a high level of metabolic adaptation to both diet type and ration size. In particular, adaptation of enzyme activities to the consumption of a diet with a high carbohydrate level suggests that a carnivorous fish like Sparus aurata can tolerate partial replacement of protein by carbohydrate in the commercial diets supplied in culture. The relationship between enzyme activities, ration size and fish growth indicates that the enzymes quickly respond to dietary manipulations of cultured fish.

Muscle delta13C change in Nile tilapia (Oreochromis niloticus) fingerlings fed on C3-or C4-cycle plants grain-based diets

The effects of grain-based diets from C3 or C4-cycle plants on muscle delta(13)C change process in Nile tilapia (Oreochromis niloticus) fingerlings were investigated. Two groups of sex reversal males Nile tilapia fingerlings were fed with isoproteic (32.0% DP) and isocaloric (3200 kcal DE/kg) diets, differing from each other by their delta(13)C. Muscle samples were collected and the carbon isotopic composition was measured. For C4 diet, the formula for the muscle delta(13)C change related to the intake time of a new diet was delta(13)C=-14.88-9.21e(-0.0209t) and the half-life (T) of the muscle carbon was 33.2 days. For C3 diet, the formula was delta(13)C=-25.43+8.59e(-0.0533t) with T=13 days. The C3 diet was considered more appropriate based on its palatability and consequent larger food intake than the C4 diet, resulting in an increased muscle delta(13)C change rate. However, for future studies, would be necessary to mix both the C3 and C4 feedstuffs to formulate diets nutritionally appropriated, with contrasting stable isotopes signatures. Tissue delta(13)C change rate is therefore indicated as a promising tool to better understand the biotic and abiotic factors that influence nutrients utilization from the diet and animal growth.

Oxidative stress and antioxidant defenses after prolonged starvation in Dentex dentex liver

The aim of this work was to evaluate the effects of prolonged starvation and refeeding on antioxidant status and some metabolic-related parameters in common dentex (Dentex dentex) liver. Fish deprived of food for 5 weeks showed a significant increase in lipid peroxidation, measured as malondialdehyde (MDA) levels. The activity of the antioxidative enzymes superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPX) in starved fish significantly increased (by 42%, 22%, and 52%, respectively), whereas glutathione reductase (GR) activity was significantly depressed by 53% compared to controls. No qualitative changes in the SOD isoenzymatic pattern were detected by nondenaturing PAGE analysis, but the isoforms corresponding to CuZn-SOD I and II were enhanced in starved fish. The activity of the enzymes indicative of oxidative metabolism, beta-hydroxyacyl CoA dehydrogenase (HOAD) and citrate synthase (CS), significantly increased (by 123% and 28%, respectively), and that of glucose-6-phosphate dehydrogenase (G6PDH) was inhibited by 56%. Oxidative damage under these circumstances is reversible since all biomarkers assayed returned to control values after refeeding. Our results show that prolonged starvation leads to a pro-oxidant situation and oxidative stress despite activation of antioxidant defense mechanisms, and that inhibition of G6PDH activity might be responsible for this failure in cellular antioxidant defenses.

Effect of food deprivation on oxidative stress biomarkers in fish (Sparus aurata)

Oxidative stress in fish (Sparus aurata) as a consequence of food restriction and fasting, has been studied. Four groups of fish were maintained for 46 days under different conditions of food supplementation: a control group with no food restriction (ratio of food/fish of 2% w/w), two groups of animals with restricted food supplement (1 and 0.5%) and a fasting group (no meal addition). Finally, all the fish were provided with food at the same ratio as the control group for the last 7 days. Sampling and weighing of fish were carried out every week and their livers were used for the analysis of known biomarkers of oxidative stress. Malondialdehyde and oxidized glutathione levels increased at the third week in fish with partial or total food deprivation, but these levels returned to normal values when the fish readapted to the control conditions. Antioxidant enzymes were also analyzed and significant increases in superoxide dismutase (SOD), glutathione reductase and glutathione peroxidase activities were found in parallel with food restriction; however catalase activity decreased in fasting fish. New SOD isoforms were detected by isoelectrofocusing in fish under food restriction at the second week, which disappeared when starved fish returned to the control conditions. These new SOD isoforms were detected before the appearance of other usual oxidative stress biomarkers.

How temperature influences muscle and cuttlebone growth in juvenile cuttlefish (Sepia elliptica) (Mollusca: Cephalopoda) under conditions of food stress

Environmental factors influencing growth during the first stages of an animal's life cycle are determinative. External factors have often been implicated in the determination of rates of development of teleost larvae; however, the first stages of development of cephalopods remain poorly studied. In view of the fact that previous studies had shown that temperature is an important factor affecting cephalopod growth, particularly at high food concentrations, in this study the effect of temperature under conditions of non-satiation were investigated. A food-stress experiment was carried out for 75 days on 80 juvenile cuttlefish (Sepia elliptica) reared under two temperatures (25 and 30°C) and two food rations of glass shrimps Acetes sibogae australis at high and low proportions (2:1, respectively). We examined the effect of temperature and feeding regime on the growth of the whole animal, cuttlebone, and muscle tissue. Mantle-muscle blocks were 15% larger at 30°C than at 25°C, with the greatest difference in the middle mantle region (21% more at 30°C), whereas cuttlebone and somatic growth varied when the combination that included either the higher temperature or the higher food ration was used. Thus, at 30°C under the low feeding regime, final dorsal mantle length (DML) and cuttlebone growth index (CGI) were higher; however, at 25°C, final DML, CGI, and survivorship increased under the higher feeding regime. It was concluded that food scarcity may exaggerate the effect of small temperature differences. The results are discussed in the light of previous findings on the growth of other cuttlefish species, cephalopods, and teleosts.

Effect of feeding time on hepatic nucleic acid, plasma T3, T4, and GH concentrations in rainbow trout

The effect of feeding time (dawn, midnight) on the growth performance and daily pattern of liver nucleic acid concentrations, plasma thyroid hormone, and growth hormone concentrations was studied in immature rainbow trout (Oncorhynchus mykiss, mean individual weight: 55 g). Fish were held in groups of 20 individuals (12 groups per treatment) and maintained in flow-through tanks supplied with river water under natural photoperiod. Food pellets (Aqualim, 49% crude protein) were delivered daily over a 30-min period by means of belt feeders. Growth performance and protein retention efficiency were higher for trout fed at dawn than for those fed at midnight, whereas both groups of fish ingested the same total amount of feed. All parameters studied showed significant daily variations. The daily patterns of liver RNA concentrations, RNA/DNA, and protein/DNA ratios were significantly different between fish fed at dawn and at midnight, indicative of a higher liver protein synthesis in the trout fed at dawn. On average, plasma thyroid hormone levels were higher and plasma GH concentrations were lower in trout fed at dawn compared with those fed at midnight. The hormonal patterns were only affected by feeding time when the fish were fed at dawn. These results suggested that the observed differences in growth and protein retention efficiency were linked to the observed differences in plasma hormone levels.

Tissue concentrations of RNA and protein for juvenile brook trout (Salvelinus fontinalis): lagged responses to fluctuations in food availability

To be useful as short-term indices of nutritional status when food availability varies, wet weight-at-length and tissue concentrations of nucleic acids and protein must covary closely with a fish's recent feeding history. We measured changes in these indices for young brook trout (Salvelinus fontinalis) (fork length: 20-34 mm) reared under alternating, 4 to 5 d periods of food provisioning and food deprivation. Weight-at-length corresponded closely with current feeding conditions, being higher when the trout were fed than when they were deprived. Concentrations of RNA and protein, however, did not correspond closely with current feeding conditions. Instead, there were significant carry-over effects whereby responses to feeding conditions experienced in one treatment period were not exhibited until the following treatment period. Food provisioning had positive carry-over effects on concentrations of RNA and protein while food deprivation had negative carry-over effects. Consequently, food-deprived trout sometimes had higher concentrations of RNA and protein than well fed trout. Since wild fish may experience short-term fluctuations in food availability, lagged responses in concentrations of nucleic acids or protein like those reported here could hamper attempts to use these biochemical measures to assess the nutritional status of juvenile fish in the field.

Food deprivation during different periods of tadpole (Hyla chrysoscelis) ontogeny affects metamorphic performance differently

Tadpoles in small, ephemeral pools whose duration and food content are unpredictable can potentially encounter substantial variation in diet composition and availability. We compared the effects of 10 days of food deprivation occurring early, midway and late in ontogeny on the metamorphic size and bioenergetic properties of Hyla chrysoscelis tadpoles. Tadpoles fed throughout ontogeny were controls. Metamorphs from tadpoles starved early and midway in ontogeny had the same snout-vent length and dry mass as controls, but the time to metamorphosis was extended by 8 and 19% respectively. Metamorphs of tadpoles starved late in development attained 85% of the length and 55% of the mass of controls, metamorphosed at the same time as controls, and suffered mortality 15 times greater than other treatments, perhaps because they were near the absolute minimum necessary level of energy reserves. There were no significant differences in percent organic matter, percent tissue water, condition index, and protein or glycogen concentrations between any experimental and control treatments. If food deprivation occurred early in development, the tadpoles caught up to the size of controls, but an extended developmental time would increase the risk of predation or habitat loss. If food reductions occur late in development, perhaps magnified by pond desiccation, tadpoles are stimulated to metamorphose at the same time as controls but at a smaller size. The bioenergetic composition of tadpoles at metamorphosis is unaffected by time of food deprivation.