Carbohydrate tolerance in the fruit‐eating fish Piaractus mesopotamicus (Holmberg, 1887)

Some fish species have a limited ability to metabolize dietary carbohydrates. An important tool for understanding carbohydrate metabolism is the application of the glucose tolerance test, which can be performed orally or intraperitoneally. To evaluate carbohydrate tolerance in the fruit‐eating fish pacu, two experiments were performed, one with oral administration by gavage of three carbohydrate types (glucose, fructose and starch, 2.0 g/kg body weight (BW)) and the other with intraperitoneal injection (IP) of glucose (500 mg/kg BW). Oral glucose resulted in an increase in plasma glucose 2 hr later with the peak at 4 hr (8.30 mmol/L), and return to baseline between 6 and 12 hr; starch administration promoted a peak after 4 hr (7.70 mmol/L), returning to the baseline at 6 hr. The administration of fructose promoted a moderate peak after 2 hr (5.71 mmol/L), and return to baseline for the time points that followed. Elevated serum cholesterol levels were observed 2 and 24 hr after administration of glucose and starch. Hepatic glycogen levels increased within 24 hr, regardless of the type of carbohydrate administered. IP glucose load resulted in a peak of plasma glucose 3 hr post injection (6.91 mmol/L), returning to baseline 6 hr later. There was a reduction in the concentration of triglycerides at 24 hr. The results demonstrate that pacu metabolize both oral (glucose or starch) and intraperitoneal (glucose) carbohydrate loads after 6 hr, suggesting good ability to deal with dietary carbohydrates.     

Effects of long-term silymarin oral supplementation on the blood biochemical profile of rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)

Silymarin, an extract from “milk thistle” (Silybum marianum) plant is traditionally used as herbal medicine. The present study was conducted to investigate the clinical effects and possible side effects of silymarin on biochemical blood parameters of rainbow trout (Oncorhynchus mykiss). Fishes were treated with 0 (control), 100, 400, and 800 mg of silymarin per kg of food during 4 weeks. Plasma alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), alkaline phosphatase (ALP), creatine kinase (CK), glucose, total protein, creatinine, triglyceride, cholesterol, urea, uric acid and liver cellular total antioxidant, and protein content were measured after 7, 14, and 28 days of silymarin treatment. The results showed that oral administration of silymarin in fish significantly reduced plasma glucose and cholesterol levels and relatively increased plasma total protein and globulin concentrations (P < 0.05). Increasing plasma albumin levels indicate the important role of albumin in drug transportation in circulatory system of fish. Silymarin also stabilized cellular membrane structure and regulated the levels of AST, ALT, ALP, CK, and LDH activity. In conclusion, on the basis of these results, oral administration of silymarin up to 400 mg per 1 kg of food has no side effect on blood biochemical and clinical parameters of fishes. However, oral administration of 800 mg/kg- of silymarin caused cytotoxicity and modifications in blood biochemical parameters of fish.     

Effect of dietary L‐carnitine supplementation on growth performance and lipid metabolism in Rhynchocypris lagowski Dybowski fed oxidized fish oil

Lipid content of a diet is very susceptible to oxidation, which has many negative effects on farmed animals. Therefore, this study studied the protective effect of L‐carnitine (LC) on fish body stimulated by oxidized fish oil (OFO) from lipid metabolism. Lipid content of the diet was replaced by OFO in 0, 100 and 400 meq/kg. L‐carnitine was added to the diet in two levels, 500 and 1,000 mg/kg, giving a total of seven experimental diets. A total of 735 healthy Rhynchocypris lagowski Dybowski with an initial weight of 4.48 ± 0.14 g after 2‐week adaptation randomly divided into 15 glass aquariums. Fish were fed satiated three times daily. After 8 weeks, biometry was done to evaluate growth performance, and hepatopancreas and muscle samples were taken for biochemical analysis. The result showed that feeding with OFO had negative growth. However, in fish received both OFO and LC, growth indices improved slightly (p > .05). Feeding with OFO and LC, the content of EPA, DHA and PUFA in the muscle of R. lagowski was significantly higher than that in the control group (p < .05), which reached the maximum value in the OFO100 + LC500 group. The content of SFA, MUFA, ∑n‐6 and PUFA in hepatopancreas increased significantly (p < .05), and the content of SFA reached the maximum in OFO100 + LC500 group. Feeding with OFO increased hepatopancreas total cholesterol, triacylglycerol, HDL/LDL ratio, FAS and ACCα that involved in lipid synthesis enzymes, while reduced HL and HSLα enzyme activity and gene expression that associated with lipid decomposition. Dietary LC moderated the effects of OFO on lipid metabolism. According to the result of the present study, it can be argued that feeding of R. lagowski with OFO has negative effects on growth performance and lipid metabolism, whereas LC dosages used in this study have increased the oxidation rate of fatty acids in the hepatopancreas of R. lagowski and improved the accumulation of fat in hepatopancreas cells induced by oxidized fish oil.     

Fasting and refeeding lead to more efficient growth in lean pacu (Piaractus mesopotamicus)

We evaluated whether body fat content affects the energetic metabolism and growth in pacu submitted to daily feeding, fasting and refeeding. For 15 days, fish were fed different diets to obtain lean and fat conditions, and then subjected, for 20 days to: (1) continuously feeding (control), or (2) fasting for 15 days and refeeding for 5 days. Blood (glucose, triglycerides, cholesterol, non‐esterified fatty acids and total protein) and tissue (liver lipid and glycogen, muscle lipid and mesenteric fat) metabolic indicators, and growth performance parameters (weight gain, specific growth rate, daily feed intake and feed conversion ratio) were measured. Fasting led both lean and fat pacu to make notable use of their energy reserves, through glycogenolysis and lipolysis, reflected in reduced blood glucose and triglycerides, liver glycogen and muscle lipid levels. Lipolysis was confirmed by the high levels of non‐esterified fatty acids, especially in fat pacu. Refeeding led to higher plasma glucose and liver lipid in lean fish. Muscle fat increased in fat fish but was not restored in lean fish, while mesenteric fat index (MFI) remained the same in fat fish and increased in lean fish. Although refeeding occurred only for 5 days, lean fish grew more and were more efficient at utilizing food (higher weight gain and better feed conversion ratio). In conclusion, our results suggest that fat pacu have higher glycogenic and lipogenic abilities, and the higher deposition of lipids in fish does not mean higher availability of energy for growth when compensatory growth is stimulated by refeeding after fasting.     

Optimum protein‐to‐lipid ratio requirement of the juvenile shi drum (Umbrina cirrosa) as estimated by nutritional and histological parameters

The shi drum is an emerging Mediterranean aquaculture species that has gained increasing interest in recent years. However, the nutrient requirements of this species remain to be determined to optimize its culture. The present study evaluated the effects of dietary protein (470g/kg or 520g/kg) to lipid ratios (100g/kg, 150 or 200g/kg) on the growth performance, nutrient utilization and tissue morphology of the shi drum (7 g average initial weight). Dietary protein levels positively correlated with weight gain, showing high protein demands (>470g/kg) for this species. Nonetheless, dietary lipid levels negatively affected growth rate, feed intake and efficiency, and protein utilization, suggesting that this macronutrient cannot be efficiently utilized in high concentrations (>100g/kg). Histological evaluation revealed fat accumulation within the hepatocytes and the enterocytes with increasing dietary lipid levels, starting from 150g/kg lipid inclusion. Overall, our results confirm the high dietary protein requirements of the shi drum (>470g/kg for fish of 7 g initial weight) and suggest that lipid levels should not exceed 100g/kg of inclusion in the diets as this species has a low tolerance to this macronutrient.     

Effects of α‐lipoic acid on growth performance,body composition,antioxidant profile and lipid metabolism of the GIFT tilapia (Oreochromis niloticus) fed high‐fat diets

The wide use of lipid as a non‐protein energy substitute has led to lipid metabolic problems in cultured tilapia. Therefore, studies that reduce the effects of high‐fat diets in genetically improved farmed tilapia (GIFT) are required. This study evaluated the optimum level and effects of dietary α‐lipoic acid (α‐LA) on growth performance, body composition, antioxidant capacity and lipid metabolism of GIFT tilapia. The basal diet (120 g/kg lipid) was supplemented with six concentrations of α‐LA at 0 (control), L300, L600, L900, L1200 and L2400 mg/kg diet to make the experimental diets, which were fed to GIFT tilapia juveniles (initial body weight: 0.48 ± 0.01 g) for 8 weeks. The weight gain of fish improved significantly in the L300 than other dietary treatments. The intraperitoneal fat index and lipid content of fish fed on the L2400 diet decreased significantly than those fed on the control diet. The activities of superoxide dismutase and glutathione peroxidase (GSH‐Px) in serum and liver were significantly higher in fish fed on the L300 diet than the control. The reduced GSH content of fish fed on the L300 in serum and liver was significantly higher than those fed on control diet. The malondialdehyde content in serum and liver was significantly lower in L300 than in the control. The adipose triglyceride lipase gene was significantly up‐regulated in fish fed on the L2400, but the diacylglycerol acyltransferase 2 gene was down‐regulated in adipose. The liver‐type fatty acid‐binding protein gene in the liver was significantly up‐regulated in fish fed on the L300 and L600 diets. Moreover, the acyl‐coenzyme A oxidase gene in liver was significantly up‐regulated in fish fed on the L300, L600, L900 and L1200 diets. Polynomial regression analysis indicated that 439–528 mg/kg α‐LA is an appropriate dosage in high‐fat diet to improve growth performance and relieve lipid oxidative damage by accelerating lipid catabolism and reducing lipid synthesis in GIFT tilapia.     

Growth and nutrient utilisation of blackspot seabream (<Emphasis Type="Italic">Pagellus bogaraveo</Emphasis>) under different feeding regimes

The growth and nutrient utilization of blackspot seabream was studied under self-feeding or hand feeding for 90 days. Groups of 31 fish with an initial body weight of 24 g were fed either by hand two times a day (09:00, and 18:00 h) to apparent satiety or by self-feeders. The 90 days of the feeding trial included two periods: an adaptation period (30 days) required to achieve a constant number of feed demands per day and a subsequent experimental period (60 days). Final body weight and daily growth index were unaffected by the feeding regimes. However, the marked reduction in voluntary feed intake associated with similar nutrient gain on the self-fed group resulted in improved nutrient efficiency and in subsequent increased protein, lipid and energy retentions compared to fish hand-fed at set hours. The self-fed group displayed depressed malic (<62%) and fatty acid synthetase (<35%) activities as well as reduced triacylglycerol plasma levels, which correlated positively with feed intake and, at some extent, with fish lipid content. These results indicate the ability of blackspot seabream to adjust their lipid metabolism according to fish feeding rhythm. No effect of feeding method was however observed on glycolytic hepatic activities or on glucose, cholesterol and insulin plasma levels. Self-feeders led to similar growth (DGI, 1.4–1.5) but better efficiency (FCR, 1.0 vs. 1.5), and hence, can be regarded as a helpful tool to optimize feed distribution according to this species natural rhythm. The maximal number of demands occurring between 20:00 and 21:00 h (dusk/sunset), together with the fact that 61% of the feed demands took place during the night, reveals a preferential crepuscular/nocturnal feeding pattern of this species.     

The protein requirement of grouper Epinephelus coioides at grow‐out stage

The present study was conducted to investigate the protein requirement of grouper Epinephelus coioides at grow‐out stage (initial weight of 102.8 ± 1.02 g). Six iso‐lipidic diets were formulated using white fish meal and casein as protein sources with graded levels of protein (350, 400, 450, 500, 550 and 600 g/kg). Grouper was hand‐fed twice daily to apparent satiation in triplicates for 8 weeks. The results showed that lack of protein will lead to the declined of weight gain and specific growth rate and suitable protein not only improved growth, but also reduced feed coefficient rate. In addition, high‐protein level diet significantly decreased the morphological index of grouper. For the body proximate composition analysis, the high‐protein diets (500, 550, 600 g/kg) significantly increased the protein contents in the whole body and muscle which was contrary to as observed for the lipid content. High‐protein diets significantly improved the total protein levels of plasma which were contrast to as observed in triglyceride contents. Moreso, the cholesterol content was observed to be significantly decreased after high‐protein diet supplementation. The intestinal protease activity was observed to increase significantly with increasing protein supplementation whereas a decreasing trend was observed for the lipase and amylase activity with the highest going for the groups fed diets containing 350 g/kg protein as compared to the others. The liver alkaline phosphatase, superoxide dismutase and lysozyme activity increased with increasing protein level which later decreased. On the other hand, the acid phosphatase activity showed a significant downward trend. Based on SGR, the broken‐line regression analysis showed that the optimum dietary protein level and digestible protein level of the grouper Epinephelus coioides at grow‐out stage were 466.65 and 395.79 g/kg, respectively.     

Effects of dietary lipid levels on growth,feed utilization,digestive tract enzyme activity and lipid deposition of juvenile Manchurian trout,Brachymystax lenok (Pallas)

Six isoproteic diets were designated to evaluate the effects of dietary lipid levels (from 70 to 270 g/kg) on the growth performance, feed utilization, digestive tract enzyme activity and lipid deposition of juvenile Brachymystax lenok (average initial weight 0.54 ± 0.04 g). Each diet was fed to triplicate tanks (30 fish per tank) in an indoor closed recirculating system for 9 weeks. Final body weight and weight gain were highest in fish fed 190 g/kg diet and lowest in fish fed the 70 g/kg diet. Specific growth rate of fish fed with 190 g/kg diet was significantly higher than those fed with 70 and 270 g/kg diets (p < .05). Protein efficiency ratio of fish fed with 70 g/kg diet was significantly lower than the 110–230 g/kg treatments and was not significantly different from the 270 g/kg treatment. Fish fed with 270 g/kg diet had significantly higher hepatosomatic index and viscerosomatic index than those fed with 70–190 g/kg diets (p < .05). Intraperitoneal fat ratio and the whole‐body lipid content had a trend to increase with increase in dietary lipid level. Muscle crude lipid content increased up to 190 g/kg with increase in dietary lipid level. Lipid retention decreased with increase in dietary lipid level, while no significant differences in protein intake and retention levels were observed in fish among all treatments. Lipase activity of the mixture of pyloric caeca and foregut in fish fed 190 and 230 g/kg diets was significantly higher than those fed 70 and 110 g/kg diets. Midgut and hindgut lipase activities of fish were significantly higher than those fed the 190 and 230 g/kg diets. In conclusion, based on the second‐order polynomial model of WG and FCR, this study suggested that 173.8–195.0 g/kg dietary lipid levels were appropriated for B. lenok.     

Dietary available phosphorus requirement of crucian carp,Carassius auratus

This study was carried out to evaluate the dietary available phosphorus (AP) requirement for crucian carp (Carassius auratus). Triplicate groups were fed diets containing five graded levels of AP in 15 recirculating tanks. After a 9‐week feeding experiment, weight gain (WG), specific growth rate (SGR), feed efficiency (FE) and whole‐body and vertebrae P contents were significantly increased as dietary AP increased from 1.1 to 7.6 g/kg (p < .05) and then levelled off. N and P retention was also significantly increased as dietary AP increased to 5.5 g/kg (p < .05). Condition factor, viscerosomatic index, hepatosomatic index, whole‐body moisture, muscle P content and plasma total cholesterol were not affected by dietary P levels (p > .05). Protein and ash contents of the whole body increased linearly as the dietary P level increased, but the lipid content, plasma alkaline phosphatase activities and triacylglycerol contents showed an inverse relationship. Based on WG, FE, whole‐body P content and vertebrae P content, the optimum requirement of dietary AP for crucian carp was estimated to be 8.3, 8.3, 8.0 and 7.8 g/Kg, respectively.     

Effect of dietary lipid on growth,body composition,serum biochemistry and hepatic metabolite alteration in Chinese rice field eel (Monopterus albus) fingerlings

Five isonitrogenous and isocaloric diets containing dietary lipid concentrations from 71.90 to 142.70 g/kg were formulated and fed to Chinese rice field eel Monopterus albus fingerlings (5.00 ± 0.50 g). The highest values of weight gain, specific growth rate (SGR), together with the lowest feed conversion ratio (FCR) were found in fish fed with 89.10 g/kg lipid diet. Fish fed with 71.90 g/kg diet (F1) had higher hepatosomatic index, viscerosomatic index and whole‐body crude lipid than fish in the other four treatments (p < .05). Plasma concentration of triacylglycerol and the activity of alanine aminotransferase were also higher in fish fed with F1 diet. Whole‐body fatty acid profile varied exclusively, but with a stable value of n?3/n?6 ratio. Gas chromatography–mass spectrometry‐based metabolomics identified eighteen differential metabolites (including idose, alanine, glutamic acid, serine and hypotaurine) in liver affected by dietary lipid content using PLS‐DA analysis. The subsequent pathway enrichment revealed ten affected pathways, with the top three pathways being glycine, serine and threonine metabolism; starch and sucrose metabolism; and D‐glutamine and D‐glutamate metabolism. The broken‐line model of SGR suggested that a dietary lipid concentration of 83.50 g/kg was appropriate for M. albus fingerlings.     

The optimal dietary protein level of juvenile silver sillago Sillago sihama at three dietary lipid levels

A 5 × 3 factorial growth trial was conducted to evaluate optimal dietary protein and lipid levels (dietary protein level, DP; dietary lipid level, DL) for juvenile Sillago sihama (S. sihama) (2.0 ± 0.02 g, initial weight). Fish were fed 15 diets containing 5 DPs (350, 400, 450, 500 and 550 g/kg) and 3 DLs (60, 90 and 120 g/kg) for 8 weeks. The interaction between proteins and lipids significantly influenced the feed conversion ratio, condition factor, body composition, antioxidant indices and lipase activity (p < .05). DP 450 g/kg showed the highest average final body weight. DPs 500 and 550 g/kg significantly decreased the protein efficiency ratio (p < .05). DL 120 g/kg showed the highest percentage weight gain. The low feed conversion ratio was found in diets P45L12, P55L9 and P55L12. Diet P45L12 showed high superoxide dismutase activities. DP 450 g/kg showed the lowest average malondialdehyde content. Lipase activity was increased by increasing DP (p < .05) with a fall at DP 550 g/kg. Under the present experimental conditions, the optimal DP for S. sihama was 450 g/kg under the DL 120 g/kg.     

Pharmacokinetics and tissue residues of vancomycin after oral administration in crucian carp

The pharmacokinetics and tissue residues of vancomycin in crucian carp (Carassius auratus) were studied after oral administration of a single dosage of 1 mg/kg body weight at water temperature of 18°C. The drug concentration‐time data were fitted using a two‐compartment open model with first‐order absorption. The vancomycin concentrations in plasma and tissues including muscle, liver and kidney were analyzed by means of liquid chromatography‐tandem mass spectrometry. As a result, the plasma absorption rate constant of vancomycin was 3.75/hr and the time point of maximum concentration in plasma was 3.0 hr respectively. The maximum concentration of vancomycin in plasma was 216.58 μg/L. The distribution half‐life and the elimination half‐life in plasma were 6.69 hr and 190 hr, as well as the absorption half‐life of plasma was 0.19/hr. The area under the plasma concentration‐time curve of plasma was 15.12 mg hr/L. The apparent volume of distribution of plasma was estimated to be 4.45 L/kg and the total body clearance was computed as 0.061 L hr^?1 kg^?1. In addition, the maximum tissue concentrations of vancomycin were in the order of liver > kidney > muscle. To guarantee the safety of tissue samples for consumption, it was suggested that the withdrawal time should not be less than 30 days at 18°C. All these results may provide guidance for future vancomycin treatment in aquaculture.     

Pharmacokinetics and physio‐metabolic response of single and multiple dose of fenbendazole in Labeo rohita (Hamilton, 1822) fingerlings

An experiment was carried to determine the plasma fenbendazole (FBZ) concentration and physio‐metabolic responses in juveniles of Labeo rohita (90 ± 4 g) after oral administration of single doses at 10, 20 and 50 mg, 20 mg FBZ/kg b.wt. in multiple times on 1st, 3rd and 7th day. The blood samples were collected at 0.5, 1, 2, 4, 8, 12, 24, 30, 48, 72, 96 and 120 hr, after single‐dose administration, and regularly (upto 15 day) in multiple dose. Plasma FBZ concentration was determined up to the limit of detection (LoD) of 0.09 µg/ml by HPLC. There was no parent drug detected in plasma for administration of 10 mg FBZ/kg b.wt. The drug attained the peak concentration (C_max) 1.85 and 3.09 µg/ml in plasma at 4 hr (T_max) after administration of 20 and 50mg FBZ/kg b.wt. respectively. Plasma FBZ was detectable up to 96 and 120 hr with concentration 0.09 ± 0.007 and 0.098 ± 0.006 µg/ml, respectively, after single‐dose administration of 20 and 50mg/kg b.wt. In case of multiple‐dose administration, the maximum concentration of FBZ was 1.01 ± 0.03 µg/ml on 7th day that was less than to the single dose at 50 mg/kg b.wt. However, FBZ was detected up to 11 day after multiple doses. The study revealed that the hepatic antioxidant enzymes activities like superoxide dismutase, catalase and glutathione‐S‐transferase were significantly affected by increasing FBZ in single and multiple doses. The results of the present study could reveal that single‐ or multiple‐oral administration of FBZ at 20 mg/kg b.wt. in feed as antihelminthic drug in L. rohita could be considered as the safe dose.     

Effects of exogenous dietary enzyme on growth, body composition, and fatty acid profiles of cultured great sturgeon Huso huso fingerlings

The effects of enzyme supplementation on growth, body proximate, and fatty acid composition of great sturgeon Huso huso fingerlings were investigated. Multienzyme (Kemin^?) was added to diet in different concentrations (0, 250, 500, 750, and 1,000 mg/kg). Fingerlings were randomly stocked in tanks and fed with the experimental diets three times a day at 5–10% body weight for 46 days. Fingerlings fed diets containing 250 mg/kg exogenous enzyme exhibited higher weight gain and specific growth rate. This level of enzyme in the diet significantly improved feed conversion ratio. Body protein and moisture decreased slightly when fish fed with enzyme-supplemented diets while fat increased. Fingerlings fed with 500 mg/kg enzyme in diet had higher contents of n-3 essential fatty acids and lower n-6/n-3 fatty acid ratio. Optimum growth performance in great sturgeon fingerlings can be obtained by 250 mg/kg multienzyme in the diet.     

Pharmacokinetic disposition of enrofloxacin in brown trout (Salmo trutta fario) after oral and intravenous administrations

In this study, the pharmacokinetic profile of enrofloxacin (EF) and its major metabolite, ciprofloxacin (CF), were investigated in brown trout (Salmo trutta fario) (n = 150) after intravenous (i.v.) and oral (p.o.) administrations of a single dose of 10 mg kg^− 1 body weight (b.w.) at 10 °C. The plasma concentrations of the drugs were determined by high-performance liquid chromatography (HPLC-UV) from 0.08 to 120 h. Pharmacokinetic parameters were described by the two-compartment open model for intravenous and oral administrations, respectively. After intravenous administration, the elimination half-life (t_1/2β), apparent volume of distribution at steady-state (V_ss) and total body clearance (Cl_tot) of enrofloxacin were 19.14 ± 1.51 h, 3.40 ± 0.18 L kg^− 1 and 0.14 ± 0.01 L kg h^− 1, respectively. After oral administration, the maximum plasma concentration (C_max), time of maximum concentration (t_max) and bioavailability (F%) were 2.30 ± 0.08 µg mL^− 1, 8 h and 78 ± 4%, respectively. Ciprofloxacin was not detected in the present study. The elimination half-life for enrofloxacin following oral administration was longer than values calculated for other animals. After oral administration, the mean plasma concentration was well above the minimum inhibitory concentrations (MICs)—that is, > 0.5 µg mL^− 1 at 36 h—for most gram-negative fish pathogens. It is possible and practical to obtain therapeutic blood concentrations of enrofloxacin in brown trout (S. trutta fario) using oral administration of 10 mg kg^− 1 body weight; therefore, it may be effective in the therapy for brown trout diseases.     

Effects of dietary lysolecithin on growth performance,feed utilization,intestinal morphology and metabolic responses of channel catfish (Ictalurus punctatus)

This study investigated the effects of dietary lysolecithin on growth performance, feed utilization and metabolic responses of channel catfish (Ictalurus punctatus). Fish (initial weight: 14.77 ± 0.45 g) were randomly fed one of five practical diets supplemented with graded levels of lysolecithin (0, 125, 250, 375 and 500 mg/kg) in quadruplicate groups for 10 weeks. Results showed that no significant differences in weight gain, condition factor and viscerosomatic index among all the treatments. Fish fed diet supplemented with 250 mg/kg lysolecithin had significantly decreased feed conversion ratio and significantly increased protein efficiency ratio compared to that fed the control diet. The group with 250 mg/kg of dietary lysolecithin had higher protein and lower lipid contents in the whole body, and lower lipid content in the liver than those in the control group. Groups supplemented with 250–500 mg/kg of dietary lysolecithin had significantly higher gastric and intestinal lipase activities than the control group. Dietary lysolecithin at the level of 250 mg/kg significantly increased the activities of Na⁺, K⁺‐ATPase, alkaline phosphatase, total antioxidative capacity, total superoxide dismutase, glutathione peroxidase and catalase and significantly decreased the content of malondialdehyde compared to the control diet. In conclusion, dietary supplementation of lysolecithin could confer benefits of feed utilization, body composition and antioxidative capacity of channel catfish.     

Influence of dietary l-carnitine on growth, biological traits and meat quality in Tilapia

This study was designed to determine whether l -carnitine supplementation is necessary in a tilapia diet containing low-fish meal and a high lipid level, which is beneficial economically and for the environment. The effects of dietary l -carnitine on the growth, body composition, blood traits and post-thaw drip from muscle in hybrid tilapia were investigated. Five isonitrogenous and isocaloric diets were fed to the fish with a mean body weight of 141.7 g for 168 days. The control diet contained fish meal as the major protein source with 7% lipid. Other diets contained 7% or 12% lipid, in which fish meal was largely replaced by plant proteins, and supplemented with l -carnitine or not. Results showed that supplemental dietary l -carnitine did not affect the growth performance, feed efficiency or protein efficiency ratio, while the supplementation significantly reduced the mesenteric fat ratio. Whole body and muscle proximate compositions were unaltered by any dietary treatment. The total plasma lipid, triacylglycerol and cholesterol values of tilapia fed diets with alternative plant proteins were significantly lower than those of the control fish, whereas increasing the dietary lipid content increased the aforementioned blood traits. A decrease in plasma ammonia and an increase in urea were observed in dietary l -carnitine-supplemented fish. Post-thaw drip from muscle was reduced in fish fed supplemental dietary l -carnitine. The observations of this study revealed that neither the growth performance nor the feed utilization of hybrid tilapia was improved by a dietary l -carnitine treatment, but that it did lead to a reduced mesenteric fat ratio, altered nitrogen metabolism and improved meat quality.     

Low body fat content prior to declining day length in the autumn significantly increased growth and reduced weight dispersion in farmed Atlantic salmon Salmo salar L.

Based on the regulatory effects of body fat on appetite and seasonal variations in fat deposition and growth of Atlantic salmon, the present study tested the hypothesis that body fat content prior to declining day length in the autumn can significantly modulate growth rate. The growth rate of salmon (mean initial body weight, BW = 2.3 kg) with different muscle fat content prior to autumn, subjected to natural photoperiod and temperature, during a 7‐month period (mean final BW = 6.6 kg) was studied. In August, three fish groups (HF, LF and 0.5LF group) with significantly different muscle fat content (HF = 16.4%, LF = 13.2% and 0.5LF = 11.3%), individually marked with PIT‐tag, were mixed into the four net‐pens and fed a standard high‐energy diet until March the following year. The muscle fat content prior to the autumn had a highly significant (p < .0001) effect on growth during the 7‐month main‐dietary period, even after identical fat stores among the groups were restored, indicating a more complex explanation than just a lipostatic regulation mechanism. Mean thermal growth coefficients were HF = 2.9, LF = 3.4 and 0.5 LF = 3.9, resulting in increased final weight gain for LF and 0.5LF of 590 g and 980 g, respectively, compared to the HF group. The LF groups obtained a significantly higher homogeneity in BW and shape than HF‐fed fish in March, optimizing automatic gutting and filleting at slaughter. The improved growth response among the LF groups by reducing lipid levels can potentially be utilized in closed and semi‐closed production units where photoperiod can be manipulated.