Effect of sex and protein level on the intermediary metabolism,growth, deposition of nutrients and profile of volatile compounds of silver catfish (Rhamdia quelen)

This study aimed at evaluating the intermediary metabolism, growth, nutritional deposition and volatile compounds of fillet of female and male silver catfish created in cages having commercial diets at two levels of crude protein. A total of 1,200 silver catfish were randomly distributed in 12 cages with initial weight of 130.05 ± 0.14 g and visually sexed. Commercial diets with 280 g/kg and 320 g/kg of crude protein were offered twice a day in the amount of 30 g/kg their biomass/day, for 90 days. At the end of the experimental period, biometry was performed to collect data, blood and tissue for later determination of plasma metabolites, hepatic metabolites, digestive enzymes, volatile compounds, deposition of nutrients and calculation of growth variables. There were metabolic differences due to the sex of silver catfish, reflecting greater productive efficiency on the females. For the plasma metabolites, in male, there were higher values of triglycerides and free amino acids than in female. For hepatic glucose, males fed with diet containing 280 g/kg of crude protein showed higher values. For protein and free amino acids, the interaction between males that received 320 g/kg of crude protein was higher. In males, there were higher values of AST and hepatic glycogen than in females. In turn, hepatic ammonia was higher in females. There was greater activity of acid protease enzymes and trypsin in the silver catfish that received diets containing 320 g/kg of crude protein. Regardless of sex, in this cultivation phase, diets with 320 g/kg of crude protein provided better performance to silver catfish. The profile of volatile compounds suggests mild odour for the fillet of silver catfish, which can be a competitive advantage of the species.     

Determination of methionine requirement of juvenile silver catfish (Rhamdia quelen) and its effects on growth performance,plasma and hepatic metabolites at a constant cystine level

This study was performed to determine the dietary methionine requirements and its effects on growth performance, plasma and hepatic metabolites for juvenile silver catfish. The fish (initial weight = 3.26 ± 0.3 g) were distributed in 24 experimental units (35 fish each). Six diets were formulated with increasing levels of methionine (09, 16, 23, 30, 37 and 44 g/kg protein diet). Each diet was distributed randomly to the groups, with four replicates fed twice daily to apparent satiation for 15 weeks. Methionine levels influenced in body composition (moisture and ash), and submit effect on liver metabolism and plasma. The relative weight gain (RWG) and specific growth rate (SGR) increased with highest levels of methionine to 30 g/kg protein in the diet, thereafter maintaining a nearly constant level of 1.9 g/kg cystine in the protein diet. The protein retention coefficient (PRC) also increased with increasing levels of up to 23 g/kg protein diet, thereafter maintaining a constant level of 1.9 g/kg cystine protein diet until beginning to decrease at a level of 44 g/kg protein diet. In conclusion, methionine is an essential amino acid for the growth of juvenile silver catfish and exhibits an efficient capacity when provided as a synthetic amino acid. Based on the RWG and SGR data, the methionine requirement of juvenile silver catfish was estimated at 34.42 and 35.85 g/kg of the CP or 12.74 g/kg and 13.26 g/kg of the diet respectively.     

Dietary supplementation of autolysed yeast enhances growth,liver functionality and intestinal morphology in African catfish

A feeding trial was conducted to evaluate the potential of dietary supplementation of autolysed brewer's yeast (AY) on African catfish. The catfish (22.5 ± 1.15 g/fish, 20 fish 33 L/tank) were fed with either of diets (390 g/kg crude protein, 140 g/kg lipid) supplemented with 0, 3, 6 or 10 g/kg AY (n = 3). After 49 days of feeding, the final body weight and metabolic growth rate of the catfish fed 3 g/kg AY (3‐AY) diet were higher than those fed the control diet (p < .05). The lowest level (p < .05) of alanine transaminase was detected in the blood of the catfish fed 3‐AY diet. The mid‐intestinal histology of the catfish revealed no significant difference (p > .05) in intestinal perimeter ratio. However, an elevated (p < .05) abundance of goblet cells and intraepithelial leucocytes were found in the intestine of catfish fed 3, 6 and 10 g/kg AY diets, with the highest level of abundance recorded in the mid‐intestine of the catfish fed 3‐AY diet. The results suggest that dietary 3 g/kg autolysed brewer's yeast supplementation improves growth performance of African catfish without deleterious effect on liver functionality and gut morphology.     

Fish meal replaced by hydrolysed soybean meal in diets increases growth and improves the antioxidant defense system of silver catfish (Rhamdia quelen)

One of the current challenges of global fish farming is developing plant‐based proteins as a feasible substitute for fishmeal in the formulation of aquafeeds. Substitution levels of fishmeal with hydrolyzed soybean meal (HSM) in diets for silver catfish (Rhamdia quelen) were evaluated for growth, protein metabolism and antioxidant activity. The experiment was carried out in a recirculation system of 20 tanks of 250 L. A total of 300 silver catfish juveniles were used to compose five treatments and four replicates per treatment. Levels of soybean hydrolysate (0%, 5%, 10%, 15% and 20%) were tested in diets (39% protein and 3,500 Kcal) for 60 days. Silver catfish growth was higher at all inclusion levels of HSM when compared to the control diet. No change was shown for body protein deposition. The production of nitrogenous compounds in the liver and muscle was also unaffected by any of the diets. The diet containing 20% HSM promoted an increase in the amounts of non‐protein thiols in the gills and brain. The HSM substitution levels of up to 20% of fishmeal in the diet increases growth and contributes to silver catfish antioxidant activity.     

Dietary butyric acid improved growth,digestive enzyme activities and humoral immune parameters in Barramundi (Lates calcarifer)

A six‐week feeding trial was conducted to determine the effect of butyric acid (BA) inclusion in diet on performance of Barramundi (Lates calcarifer). Fish (12.0 ± 0.2 g) were fed with four experimental diets contained 0.0 (control), 2.5, 5.0 and 10.0 g BA/kg in triplicate. Fish fed on 5 and 10 g BA/kg diets had higher growth and total alkaline protease and lipase activities than the other treatments. Fillet protein content in BA‐supplemented groups was higher than the control. Liver catalase activity was highest in 2.5 g BA/kg group compared with the other groups. The values of liver superoxide dismutase activity and serum total protein concentration in 5 and 10 g BA/kg treatments were higher than those in the control (p < .05). Moreover, the highest and the lowest levels of serum lysozyme activity were noticed in the 10 g BA/kg and the control groups, respectively (p < .05). Also, the highest respiratory burst activity was observed in fish fed 5 g BA/kg feed. Supplementing diet with 2.5 or 5 g BA/kg resulted in higher serum haemolytic activity in fish compared with the other groups. The number of red and white blood cells increased in fish fed BA‐supplemented diets compared with the control (p < .05). In conclusion, the results of this study showed inclusion of BA at 5 g/kg diet in L. calcarifer juveniles improved growth and upgraded the general health condition by enhancing fish antioxidant enzyme activities and haemato‐immunological responses.     

Effect of supplemental taurine on juvenile channel catfish Ictalurus punctatus growth performance

Juvenile channel catfish (5.6 g/fish) were fed a basal diet that contained major protein (soybean meal, cottonseed meal) and energy (ground corn grain, wheat middlings) ingredients that were derived from plant sources. The basal diet was supplemented with three levels of crystalline taurine to provide 1, 2 and 5 g/kg taurine. In addition, a fifth diet that contained 80 g/kg menhaden fishmeal formulated with the same plant‐source ingredients was included as the positive control diet. Fish were fed the five diets once daily for 12 weeks. Weight gain was highest in catfish fed taurine at 2 g/kg (47.8 g/fish) compared to catfish fed the control basal diet (40.8 g/fish) and 80 g/kg fishmeal diet (41.1 g/fish) (p < .05). Among the taurine‐supplemented diets, weight gain was lowest in catfish fed taurine at 5 g/kg. Feed conversion ratio (FCR) was significantly improved in fish fed diets supplemented with taurine at 2 g/kg compared to all other treatments (p < .01). Survival during the growth study ranged from 98.0 to 99.0% (p > .05) for all treatments. The results suggest taurine supplementation to juvenile channel catfish may improve weight gain and FCR.     

Nutritional value of frass from black soldier fly larvae,Hermetia illucens,in a channel catfish,Ictalurus punctatus,diet

Frass is the by‐product of the larval meal industry and includes larval waste, exoskeleton sheds and residual feed ingredients. Experimental frass was derived from the larvae of black solder flies fed distillers' dried grains with solubles and had a protein and fat content of 216 and 60 g/kg, respectively. A 10‐week study was conducted to evaluate the effect of dietary levels of frass on growth, feed utilization, and body proximate and mineral composition of channel catfish, Ictalurus punctatus. Five diets containing 0, 50, 100, 200 and 300 g frass per kg diet were fed to channel catfish (5.24 ± 0.04 g) in quadruplicate aquaria to apparent satiation twice daily. Final weight gain was significantly increased in fish fed diets containing frass at levels from 100 to 300 g/kg. Fish fed diets without frass, and with 300 g/kg frass, showed the lowest and highest feed intake, respectively. Feed and protein efficiencies, however, were significantly lower in fish fed frass at levels of 200 g/kg and higher compared to the control diet. Survival, whole‐body composition and mineral content were not affected by frass. In summary, black soldier fly larval frass has potential as a protein source or just an ingredient for enhancing palatability of catfish diets.     

Dietary thiamin requirement of fingerling Channa punctatus (Bloch) based on growth,protein gain,liver thiamin storage,RNA/DNA ratio and biochemical composition

Dietary thiamin requirement of fingerling Channa punctatus was quantified by feeding casein/gelatin‐based diets (450 g/kg CP; 18.39 kJ/g GE) with seven graded levels of thiamin (0, 0.5, 1, 1.5, 2, 2.5 and 5 mg/kg diet) to triplicate groups of fish (6.9 ± 0.93 cm; 4.91 ± 0.62 g) for 16 weeks. Fish fed diet with 2.5 mg/kg thiamin reflected highest absolute weight gain (AWG), protein gain (PG), RNA/DNA ratio and lowest feed conversion ratio. Similarly, highest liver thiamin concentration was also recorded in fish fed 2.5 mg/kg thiamin diet. Hepatic thiobarbituric acid reactive substance (TBARS) concentration responded negatively with increasing concentrations of dietary thiamin up to 2.5 mg/kg, whereas superoxide dismutase and catalase activities were found to improve with the increasing levels of dietary thiamin from 0 to 2.5 mg/kg. Transketolase activity also improved as the thiamin concentrations increased up to 2.5 mg/kg. Broken‐line regression analysis of AWG, PG, RNA/DNA ratio, liver thiamin concentrations, transketolase and TBARS activities exhibited the thiamin requirement in the range of 2.34–2.59 mg/kg diet. Data generated during this study would be useful in formulating thiamin‐balanced feeds for the intensive culture of this fish.     

Dietary organic acid salts mitigate plant protein induced inflammatory response and improve humoral immunity,antioxidative status and digestive enzyme activities in yellowfin seabream,Acanthopagrus latus

An eight‐week research was conducted to investigate the effects of single or combined administration of sodium propionate (Na‐P) and sodium acetate (Na‐A) on the performance of yellowfin seabream (Acanthopagrus latus) juveniles (6.5 ± 0.3 g). A plant protein (PP)‐rich diet was supplemented with sole or blends of organic acid salts (OAS) namely Na‐P and Na‐A to design six experimental feeds including control (without OAS), Na‐P5 (5 g/kg Na‐P), Na‐P10 (10 g/kg Na‐P), Na‐A5 (5 g/kg Na‐A), Na‐A10 (10 g/kg Na‐A) and Na‐P + A (5 g/kg Na‐P + 5 g/kg Na‐A). Except for Na‐A5 group, the other OAS‐supplemented treatments had higher growth and feed efficiency ratio than the control (p < .05). The inclusion of OAS in the experimental feeds pronouncedly enhanced plasma lysozyme and alternative complement pathway activities compared to the control. Furthermore, fish fed on the OAS‐supplemented diets had greater catalase and glutathione peroxidase activities in the liver than the control (p < .05). Total antioxidant capacity in the liver of fish fed on the OAS‐supplemented diet also was higher than the control. Fish fed on the OAS‐supplemented diets had higher pepsin, trypsin and lipase activities than the control. The insulin‐like growth factor 1 (IGF‐1) gene expression was remarkably down‐regulated in the liver of fish fed on the OAS‐supplemented diets compared to the control especially in groups fed on the Na‐P10 and Na‐A10 diets. The greatest IGF‐1 gene down‐regulation level in the gut was in fish fed on the Na‐P5 and Na‐P10 diets. The interleukine‐1β in the gut was remarkably up‐regulated in the control compared to the other groups (p < .05). The lactic acid bacterial colonies count in the gut of the control was lower than the OAS‐supplemented groups. Based on the findings of the present study, supplementing PP‐rich diets with 10 g/kg Na‐P or blends of Na‐P (5 g/kg) and Na‐A (5 g/kg) beneficially alleviated inflammatory responses and improved immune parameters and digestive capacity in yellowfin seabream juveniles.     

Effect of Lactobacillus acidophilussupplementation on growth performances,digestive enzyme activities and gut histomorphology of striped catfish (Pangasianodon hypophthalmusSauvage, 1878) juveniles

The influence of dietary supplementation of Lactobacillus acidophilus, on growth performance, digestive enzyme activities, gut histomorphology and gut microflora were evaluated in juveniles striped catfish (Pangasianodon hypophthalmus). Five experimental diets were formulated by supplementing 0, 10³, 10⁵, 10⁷ and 10⁹ CFU/g L. acidophilus in fishmeal and casein‐based semi‐purified diet. Triplicate groups of striped catfish (21.69 ± 0.18 g) were stocked in 15 fiberglass tanks with stocking density of 25 individuals per tank and fed twice daily at 2.5% of the fish body weight for 12 weeks. Weight gain, specific growth rate, feed conversion ratio and the protein efficiency ratio were significantly higher in fish fed with 10⁵ and 10⁷CFU/g L. acidophilussupplemented diets compared with the other treatment groups. Compared with the control and fish fed low (10³ CFU/g) L. acidophilus supplementation, those fed with 10⁵ and 10⁷ CFU/g had significantly higher (p < 0.05) apparent protein digestibility. Inclusion of L. acidophilus at 10⁷ CFU/g diet significantly increased amylase, protease and lipase activities. Microscopic analysis showed that the villi length in both the anterior and posterior gut and microvilli length in the posterior gut increased significantly in fish fed L. acidophilus supplementation at 10⁵ and 10⁷ CFU/g of diet. The fish fed L. acidophilus supplemented diets significantly increased the total lactic acid bacteria counts in the gut of striped catfish compared with the control‐fed group. Based on gut histomorphology and growth performance, inclusion of L. acidophilus at 10⁵ CFU/g appears to have the most positive effect on striped catfish farming.     

Effect of dietary vitamin C on growth performance,body composition and biochemical parameters of juvenile Chu's croaker (Nibea coibor)

Vitamin C is an essential micronutrient for normal physiological and immune functions of fish. However, its requirements and effects in Chu's croaker (Nibea coibor) are currently unknown. A 56‐day feeding trial was conducted to evaluate the optimal dietary vitamin C requirements based on its effects on growth performance, body composition and biochemical parameters in juvenile Chu's croaker (14.17 ± 0.1 g). Six isoproteic (450 g/kg crude protein) and isolipidic (100 g/kg crude lipid) diets were formulated to contain 2.24 (basal diet), 39.03, 85.01, 171.16, 356.49 and 715.46 mg/kg of vitamin C. The results showed that fish fed on 171.16 mg/kg vitamin C diet had the highest growth performance and feed utilization. Fish fed on the basal diet had higher malondialdehyde (MDA) content and lower activities of antioxidant enzymes in the serum and liver as compared with those fed on vitamin C diets. Polynomial analysis indicated that the optimal dietary vitamin C requirements of juvenile Chu's croaker were 102.28, 98.21, 150.26, 165.38, 71.46, 176.19, 84.84 and 103.78 mg/kg based on weight gain, specific growth rate, liver storage, muscle storage, liver MDA content, liver alanine aminotransferase activity, liver alkaline phosphatase activity and liver superoxide dismutase activity, respectively. We recommend an inclusion level in the range of 71.46–150.26 mg/kg vitamin C in the diets of juvenile Chu's croaker for optimum growth performance, liver function, antioxidant capacity and innate immunity functions.     

The effects of dietary inulin and Jerusalem artichoke (Helianthus tuberosus) tuber on the growth performance,haematological, blood chemical and immune parameters of Nile tilapia (Oreochromis niloticus) fingerlings

This study investigated the effects of dietary inulin or Jerusalem artichoke (JA) on the growth performance, haematological, blood chemical and immune parameters of Nile tilapia fingerlings. Five treatment diets were designed to incorporate inulin at 0 (basal diet), 2.5 and 5.0 g/kg and JA at 5.0 and 10.0 g/kg. Two basal diets including fish meal and formulated experimental feed were used for fry and fingerling growing periods, respectively. During the fry growing period, larvae were fed treatment diets for 4 weeks. There were no significant differences in growth performance or survival rate. Fingerlings were then nursed with the formulated experimental diets from weeks 5 to 12. Fingerlings fed on inulin at 5.0 g/kg or JA at either level had better growth performance and survival rate than that fed on the basal diets. There were no significant differences in body composition. Dietary prebiotic inulin and JA increased red blood cell number (p < .05). Among the five blood chemistry parameters examined, both inulin at 5.0 g kg and JA (5.0 and 10.0 g/kg) increased blood protein (p < .05). Dietary inulin at 5.0 g/kg and JA at 5.0 and 10.0 g/kg increased total immunoglobulin and lysozyme activity (p < .05). Both inulin and JA inclusion diets increased alternative complement activity (p < .05). Taken together, dietary inulin at 5 g/kg and JA at 5.0 and 10.0 g/kg had beneficial effects on the growth performance, survival rate and immune of Nile tilapia fingerlings.     

Functional linseed fibres and their impacts on silver catfish (Rhamdia quelen) nutrition

This study was conducted with the objective of evaluating the combination of different ratios of soluble and insoluble linseed fibre for silver catfish (Rhamdia quelen). For this, the soluble and insoluble fractions were concentrated separately and combined in four ratios (1:0.5, 1:1, 1:2, 1:4), which were added to silver catfish diets and evaluated in a bioassay. After 45 days of receiving the experimental diets, the animals were submitted to biometry to collect data and tissues. The experimental design was completely randomized, with five treatments and four replications and the means were compared by Tukey's test (p < .05). Diets 1:2 and 1:4 provided higher weight gain, specific growth rate and crude protein deposition to the fish, whereas only the 1:4 diet reflected higher crude body protein. The 1:0.5 diet altered the trypsin activity in the intestine, and, together with the 1:4 diet, it provided a higher intestinal villi height. Body yield, somatic and digestive parameters, chymotrypsin activity and glucose, glycogen and liver protein were not altered, regardless of the experimental diets. In conclusion, the results indicate that linseed fibre acts effectively as a growth promoter in silver catfish diets, with the use of 1:2 and 1:4 ratios optimizing its prebiotic action.     

Tilapia protein hydrolyzate improves growth performance,protein absorption and antioxidant status in Silver catfish (Rhamdia quelen)

This study evaluated the substitution of fish meal with tilapia protein hydrolyzate (TPH) in diets for Silver catfish (Rhamdia quelen) by verifying the effects on growth, body composition, blood and biochemical parameters, and biomarkers of oxidative stress. Five isoproteic and isoenergetic diets (37% crude protein, 3,800 kcal/kg) were produced with different substitution levels of TPH (0%, 5%, 10%, 15% and 20%) for fishmeal. The hydrolyzate was obtained by enzymatic hydrolysis from carcasses of Nile tilapia (Oreochromis niloticus), which were exposed to swine pepsin enzyme at 36°C for four hours. The experimental design was completely randomised with five treatments and four replications. The inclusion of 20% TPH in diets for silver catfish increased the growth of Silver catfish juveniles. At levels above 5%, there was an increase in body protein deposition and the efficiency of oxidative metabolism.     

Effects of dietary Nutrafito Plus on growth,haemotological parameters and total ammonia‐nitrogen excretion of juvenile striped catfish Pangasianodon hypophthalmus

A feeding trial was performed to determine the effect of a commercial source of Yucca schidigera and Quillaja saponaria extracts (Nutrafito Plus^®), in practical diets, on striped catfish Pangasianodon hypophthalmus growth, feed utilization, body composition, total ammonia‐nitrogen (TAN) excretion and haematological parameters. Four experimental diets were supplemented with Nutrafito Plus^® at 0%, 0.01%, 0.02% and 0.03% (diets: control, N01, N02 and N03 respectively). Three replicate groups of striped catfish, with initial mean weight of 1.78 ± 0.05 g, were fed one of the four diets for 12 weeks. The specific growth rate (SGR) and final weight of fish fed diet N03 was significantly higher (P < 0.05) than fish fed the other dietary treatments. The growth performance of fish fed diets N01 and N02 were not significantly different compared to fish fed the control diet. Striped catfish fed diet N03 had improved feed conversion ratio (FCR), net protein utilization (NPU) and protein efficiency ratio (PER) than the control (P < 0.05). The inclusion of the high dietary level of Yucca schidigera and Quillaja saponaria, diet N03, reduced TAN compared to all groups. Dietary inclusion of Yucca schidigera and Quillaja saponaria at all levels investigated did not affect the whole body proximate composition of the striped catfish (P > 0.05). The packed cell volume (PCV) and haemoglobin level in fish fed diet N03 was significantly higher than in the fish fed the control diet. The present study demonstrates that dietary inclusion of Yucca schidigera and Quillaja saponaria induced positive effects on growth performance and haematological parameters and decreased TAN excretion in striped catfish.     

Effects of olive pomace on growth performance,digestibility, body composition and fatty acid profile in yearling Siberian sturgeon,Acipenser baerii (Brandt 1896)

Replacement of olive pomace (OP) with wheat flour in diet was studied in diet of yearling Siberian sturgeon (Acipenser baerii). Fish (165 ± 6.8 g) were randomly allocated to 15 fibreglass tanks (15 fish/tank, in triplicate). Fish were assigned to one of five dietary treatments at 19.1 ± 1.5°C for 8 weeks: control diet (crude protein and crude lipid at 514.6 and 188 g/kg_, respectively) and four experimental diets with 20, 50, 75 and 100 g/kg OP to replace wheat flour in the experimental diets. No significant difference was observed in the final weight, feed conversion ratio, specific growth rate, hepatosomatic index, viscera‐somatic index and survival rate among the treatments (p > 0.05). No change was seen in digestibility of protein and lipid in diets containing 20 g/kg and 50 g/kg OP compared to control group, while these values decreased with increasing in OP above 50 g/kg. Digestibility of dry matter and gross energy among the treatments demonstrated no significant difference (p > 0.05). Polyunsaturated fatty acids, especially C22:6n3 (DHA), in the muscle of the fish fed 75 g/kg and 100 g/kg OP in diets were significantly higher than control group (p < 0.05). These data show that OP could be recommended as a substitute for wheat flour in diet of S. sturgeon but its utilization for other species warranted future works.     

Dietary ascorbic acid requirement for growth of striped catfish,Pangasianodon hypophthalmus (Sauvage, 1878) juveniles

A sixty‐day feeding trial was conducted to determine the ascorbic acid (AA) requirement for growth of striped catfish, Pangasianodon hypophthalmus juveniles. Seven iso‐nitrogenous and iso‐energetic (370 g protein per kg and 19.6 MJ/kg) purified diets were prepared with different levels of ascorbic acid such as control (0), T₁ (17.5), T₂ (35), T₃ (70), T₄ (175), T₅ (350) and T₆ (700) mg ascorbic acid (L‐ascorbyl‐2‐polyphosphate) equivalent per kg diet. Fish with a mean body weight of 3.2–3.4 g were stocked (fifteen fish per tank) in triplicates following a completely randomized design. Each group was fed to satiation twice a day for 60 days. Significant differences were observed in growth, survival, body composition and metabolic enzymes activities with different dietary ascorbic acid levels. Maximum weight gain, specific growth rate (SGR) and protein efficiency ratio (PER) were found in fishes fed with 35 mg AA per kg diet, supported by best feed conversion. Fish fed a diet containing vitamin C had the highest activities of aspartate aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphatase (ALP) compared to those fed with vitamin C‐depleted diets. In this study, based on using broken‐line regression analysis, the dietary vitamin C requirement for growth of P. hypophthalmus juveniles was estimated to be in the range of 46–76 mg AA per kg, depending on the criterion used, growth and liver storage. Our results will be helpful for the formulation of cost‐effective ascorbic acid incorporated diets for striped catfish, P. hypophthalmus.     

Evaluation of immune response and performance of silver catfish fed functional linseed fibres in response to hypoxia stress

This study was conducted to evaluate the immunostimulating activity and growth promoting of diets supplemented with different rations of soluble and insoluble linseed fibre to Rhamdia quelen under hypoxia‐induced acute stress. For this reason, soluble and insoluble fractions of linseed fibre were concentrated separately and combined into four ratios (1:0.5; 1:1; 1:2 and 1:4), which were added to the diets of silver catfish (6.43 ± 0.12 g) and evaluated in a biological assay, along with a control diet (without addition of linseed fibre). After being fed the experimental diets for 45 days, specimens of silver catfish were submitted to hypoxia‐induced acute stress. They were kept out of water for 60 s. Immediately afterwards, blood and cutaneous mucus were collected for subsequent determination of immunological indicators and stress. After stress, the fish were weighed and measured for performance parameter calculation. The experimental design was completely randomized with five treatments and four replications. The data underwent analysis of variance and the means were compared by Tukey's test (p < .05). The fish fed diets containing the 1:2 and 1:4 soluble:insoluble fibre ratios, showed higher total protein content, globulin, plasma alkaline phosphatase activity, and performance in addition to higher mucoprotein content in the cutaneous mucus of the fish. Regardless of their ratio in the diet, linseed fibre provided higher plasma levels of total immunoglobulins and reduction in cortisol levels. The 1:1, 1:2 and 1:4 diets led to higher levels of total immunoglobulins and alkaline phosphatase activity in cutaneous mucus. The results indicate that linseed fibre has a stress‐ reduction, immunostimulant and a growth promoter effect on silver catfish. The 1:2 or 1:4 soluble: insoluble fibre ratios provided greater stimulation of the target immunological indicators and performance.     

Effect of dietary iron (Fe) levels on growth performance,hepatic lipid metabolism and antioxidant responses in juvenile yellow catfish Pelteobagrus fulvidraco

This study was conducted to determine effects of dietary Fe levels on growth performance, hepatic lipid metabolism and antioxidant response for juvenile yellow catfish Pelteobagrus fulvidraco. Yellow catfish were fed six isonitrogenous and isolipidic diets containing Fe levels of 16.20, 34.80, 54.50, 76.44, 100.42 and 118.25 mg/kg for 8 weeks. Weight gain (WG) and specific growth rate (SGR) increased with dietary Fe levels from 16.20 to 54.50 mg/kg diet and then plateaued over the level. Feed conversion rate (FCR) was highest and protein efficiency rate (PER) was lowest for fish fed the lowest Fe levels of diet. Fe contents in whole body and liver increased with increasing dietary Fe levels. Hepatic lipid content was lowest, but mRNA levels of carnitine palmitoyltransferase (CPT‐1) and peroxisome proliferator‐activated receptor α (PPARα) were highest for fish fed 54.50 mg Fe/kg diet. Fish fed adequate dietary Fe levels reduced hepatic malondialdehyde (MDA) level and increased activities of antioxidant enzymes Superoxide dismutase (SOD), Catalase (CAT) and GS. Based on the broken‐line regression analysis of WG against dietary Fe levels, optimal dietary Fe requirement for yellow catfish was 55.73 mg Fe/kg diets. Fe‐induced changes in MDA levels and antioxidant enzymatic activities paralleled with the change in hepatic lipid content, suggesting the potential relationship between oxidative stress and hepatic lipid accumulation in yellow catfish.     

Atlantic salmon fed a nutrient package of surplus methionine,vitamin B12, folic acid and vitamin B6 improved growth and reduced the relative liver size,but when in excess growth reduced

Feeding plant‐based diet through smoltification of Atlantic salmon requires verification of the optimal level of 1C nutrients. Here, we fed Atlantic salmon plant‐based diets containing three different surplus amounts of the 1C nutrients; methionine, cobalamin (vitamin B12), pyridoxine (vitamin B6) and folic acid during 6 weeks in fresh water, through smoltification, followed by 3 months on‐growing period in salt water. The three diets were fed to fish dispersed in triplicate tanks throughout the experiment. Mean start body weight was 32 g. Dietary methionine levels in the diets were 6.7, 9.2 and 11.7 g/kg. Dietary B6 was 6.75, 8.45 and 11 mg/kg. Cobalamin was 0.16, 0.18 and 0.20 mg/kg. While dietary folic acid was 2.9, 4.8 and 6.3 mg/kg, diets are referred to as low, medium and high 1C diet. All other amino acids were similar between diets. The results showed no differences in growth or feed utilization in the fresh water period, but following the on‐growing salt water period, differences between diets occurred. The fish fed the medium 1C diet showed better growth, as compared to fish fed the low or high 1C diet (p = .009). The medium 1C fed fish showed a relative lower liver weight compared with fish fed low or high 1C diet (p = .025). Condition factor was better in fish fed the medium and high 1C diet as compared to those fed the low 1C diet (p = .0006). As expected, free methionine in liver, plasma and muscle increased by dietary methionine inclusion. Surplus vitamins only had minor effect on tissue concentrations. Based on these findings, we conclude that the micronutrient and methionine level presented in the medium 1C diet improved the growth, liver size and condition factor; however, more research is needed to evaluate the optimal requirement level for each of the 1C nutrients.