Effect of natural free gossypol and gossypol‐acetic acid on growth performance and resistance of channel catfish (Ictalurus punctatus) to Edwardsiella ictaluri challenge

A study was conducted to evaluate the effect of free gossypol from glanded‐cottonseed meal (G‐CSM) (natural free gossypol) or gossypol‐acetic acid on growth performance, body composition, haematology, immune response and resistance of channel catfish (Ictalurus punctatus) to Edwardsiella ictaluri challenge. Soya bean meal‐based diets supplemented with 0, 100, 200, 400, and 800 mg kg^?1 free gossypol from G‐CSM or gossypol‐acetic acid were fed to juvenile channel catfish in triplicate aquaria to apparent satiation twice daily for 12 weeks. Neither sources nor levels of dietary gossypol significantly influenced the final weight gain, feed intake, feed efficiency and survival of channel catfish. Similarly, whole‐body proximate composition, haematological parameters (red blood cell, white blood cell counts, haemoglobin and haematocrit), serum protein concentration, macrophage chemotaxis ratio, phagocytic activity and antibody production against E. ictaluri 21‐day postinfection were not significantly affected at either dietary sources or levels of gossypol. Gossypol concentrations of liver were linearly related to dietary level of gossypol but the retention rate varied dependent on sources of the dietary gossypol. At dietary gossypol levels of 400 or 800 mg kg^?1, total gossypol concentrations in liver of fish fed dietary gossypol from G‐CSM were significantly higher than those of fish fed the corresponding levels of gossypol from gossypol‐acetic acid. The (+)‐isomer of gossypol was predominantly retained in liver regardless of dietary sources of gossypol. The ratio of (+) to (?) gossypol isomers in liver decreased with increasing dietary concentrations of gossypol. Serum lysozyme activity of fish fed dietary gossypol levels of 200 mg kg^?1 or higher, either from G‐CSM or gossypol‐acetic acid, was significantly higher than that of the control. At a level of 800 mg kg^?1 diet, gossypol from G‐CSM stimulated significantly higher lysozyme activity than gossypol from gossypol‐acetic acid. Fish fed diets containing 400 mg kg^?1 gossypol or higher from G‐CSM or 800 mg kg^?1 gossypol from gossypol‐acetic acid had significantly increased superoxide anion (O) production. However, neither the sources nor the levels of dietary free gossypol influenced the resistance of juvenile channel catfish to E. ictaluri challenge.     

A study on dietary l‐lysine requirement of juvenile yellow catfish Pelteobagrus fulvidraco

An 8‐week feeding trial was conducted to determine lysine requirement of juvenile yellow catfish (Pelteobagrus fulvidraco) by feeding formulated diets containing crystalline l ‐lysine. Six isonitrogenous and isoenergetic diets (405 g kg^?1 protein, 18 kJ g^?1 gloss energy) containing fish meal together with soybean protein concentrate as protein sources and fish oil together with soybean oil as lipid sources were formulated. Crystalline l ‐lysine was added into the six diets to acquire lysine concentrations of 17.3, 21.8, 26.0, 31.3, 35.5 and 41.9 g kg^?1 dry diets, respectively. Mixture of crystalline amino acid was supplemented to simulate the amino acid profile in muscle of yellow catfish. The results indicated that final body weight (FBW), weight gain (WG), specific growth rate (SGR), feed efficiency (FE) and protein efficiency (PE) increased with the increase in dietary lysine level from 17.3 to 31.3 g kg^?1 of diet and then decreased as the dietary lysine levels further increased. No significant difference in survival rate was found among all the dietary treatments. One‐slope, quadratic broken‐line analysis on the basis of SGR showed that the dietary l ‐lysine requirement of juvenile yellow catfish was 33.1 g kg^?1 of dry diet (83.2 g kg^?1 of dietary protein).     

Dietary copper requirement of juvenile yellow catfish Pelteobagrus fulvidraco

The present experiment was conducted to quantify dietary copper (Cu) requirement for juvenile yellow catfish Pelteobagrus fulvidraco. The six experimental diets were formulated to contain the graded levels of CuSO₄·5H₂O (0, 0.005, 0.01, 0.02, 0.04 and 0.08 g kg^?1 diet respectively) providing the actual dietary copper values of 2.14 (control), 3.24, 4.57, 7.06, 12.22 and 22.25 mg Cu kg^?1 diet respectively. Each diet was fed to triplicate groups of yellow catfish (initial body weight: 3.13 ± 0.09 g, means ± SD) in an indoor static rearing system for 7 weeks. Fish fed the diet containing 3.24 mg Cu kg^?1 diet had the highest weight gain and specific growth rate, but they were not significantly different from that of fish fed the 4.57 and 7.06 mg Cu kg^?1 diets (P > 0.05). The poorest feed conversion rate, the lowest protein efficiency ratio, the lowest hepatosomatic index and viscerosomatic index were observed in fish fed the diet containing the highest Cu content diet (P < 0.05). Condition factor showed no significant differences among the treatments (P > 0.05). Proximate composition of fish body was significantly affected by dietary copper level (P < 0.05). Cu contents of whole body and liver increased with dietary Cu levels (P < 0.05), but muscle Cu content remained relatively stable (P > 0.05). Analysis by the second‐order regression of SGR and linear regression of whole‐body Cu retention of the fish indicated that dietary Cu requirements in juvenile yellow catfish were 3.13–4.24 mg Cu kg^?1 diet.     

Approaches to optimizing dietary protein to energy ratio for African catfish Clarias gariepinus (Burchell, 1822)

An 8‐week feeding trial was conducted in a recycling water system at 28 ± 1 °C to investigate protein to energy ratio (P/E ratio) in African catfish Clarias gariepinus (10.9 ± 0.04 g). Six fishmeal‐based diets of two protein levels (330 and 430 g kg^?1), each with three lipid levels (40, 80 and 120 g kg^?1) resulted in P/E ratios ranging from 15.5 to 21.3 mg protein kJ^?1 gross energy (GE) were fed to 20 fish (per 30‐L tank) in triplicate. Fish were fed 50 g kg^?1 of their body weight per day adjusted fortnightly. Significantly higher (P < 0.05) growth rates and feed conversion efficiency were evident in fish fed with higher protein diet. The highest growth rate was found by fish fed 430 g kg^?1 protein, 21.2 kJ^?1 GE with a P/E ratio of 20.5 mg protein kJ^?1 GE. Significantly indifferent (P > 0.05) values of protein utilization were found in‐between the both (higher and lower) protein diets. Higher lipid deposition (P < 0.05) in whole body and liver was observed with increasing dietary lipid level at each protein diet and as higher (P < 0.05) for the lower protein diets. Liver glycogen tended to decrease with increasing gross energy at each protein diet and higher protein diet showed comparatively lower values (P > 0.05). Digestive enzyme activities (protease and lipase) and histological examination of intestine and liver of fish fed varying P/E diets found no significant differences in response to experimental diets. The study reveals that African catfish C. gariepinus performed best the diet containing 430 g kg^?1, 21.2 kJ g^?1 and 20.5 mg protein kJ g^?1 GE protein, gross energy and P/E ratio, respectively.     

Effects of brewer’s yeast extract on growth performance and health of juvenile pikeperch Sander lucioperca (L.)

Juvenile European pikeperch, Sander lucioperca, were fed commercial feed (group C) or experimental feed supplemented with NuPro^® nucleotide‐rich Saccharomyces cerevisiae yeast protein (extract obtained through a cell wall removal process) in doses of 20, 40 or 60 g kg^?1 feed (groups N2, N4, N6) for 8 weeks. Growth, non‐specific immunity parameters, histological structure of the liver and intestine, proximate whole‐body composition and blood biochemical parameters were assayed. It was noted that brewer’s yeast extract has immunomodulatory proprieties. NuPro^® in doses of 40 and 60 g kg^?1 feed strongly stimulated non‐specific (innate) cellular and humoral immunity in pikeperch. The experimental feed did not have a significant impact on pikeperch growth (P > 0.05). The proximate composition of the fish bodies and the hepatosomatic and viscerosomatic (VSI) indices were also not affected, which indicated that the tested diets had no negative impact on the metabolism or deposition of nutrients in fish tissues. The lower levels of transaminases AST and ALT, which were noted in the groups with the two highest doses of NuPro^® (P < 0.05), might indicate improved liver function. It was also demonstrated that the brewer’s yeast extract stimulates the absorption activity of intestinal epithelial cells.     

Dietary available phosphorus requirement of juvenile walking catfish,Clarias leather

A feeding trial was conducted to evaluate the optimum requirement of dietary available phosphorus (AP) for juvenile walking catfish, Clarias leather. Six practical diets were formulated to contain graded levels (2.2, 3.9, 5.5, 7.1, 8.8 and 10.4 g kg^?1) of AP from dietary ingredients and monocalcium phosphate. Each diet was randomly fed to triplicate groups of fish with initial mean weight of 7.94 ± 0.08 g in floating cages (1.5 × 1.5 × 2.0 m) suspended in an earthen pond, and each cage was stocked initially with 60 fish. Fish were fed thrice daily (07:30, 13:00 and 17:30) to apparent satiation for 10 weeks. Both specific growth rate (SGR) and protein efficiency ratio significantly increased with increasing AP from 2.2 to 5.5 g kg^?1 (P < 0.05) and then levelled off. Dietary AP levels significantly influenced whole‐body protein, lipid and ash contents as well as condition factor and hepatosomatic index (P < 0.05). Whole‐body and vertebrae phosphorus contents showed similar patterns as SGR in response to dietary AP content. Broken‐line analyses based on SGR, phosphorus contents in the vertebrae and whole‐body indicated the AP requirements were 5.8, 7.2 and 7.5 g kg^?1, respectively.     

Growth, feed efficiency and body mineral composition of juvenile vundu catfish (Heterobranchus longifilis, Valenciennes 1840) in relation to various dietary levels of soybean or cottonseed meals

This study aimed to assess the effect of soybean meal (SBM) and cottonseed meal (CSM), as partial replacement of dietary fish meal on growth, feed efficiency (FE) and body mineral composition of juvenile vundu (Heterobranchus longifilis). Five iso‐nitrogenous (390 g kg^?1 crude protein) and iso‐caloric (18 kJ g^?1, gross energy) diets (Control, SBM30, SBM60, CSM30 and CSM60) were fed to triplicate groups of 40 fish (initial mean weight: 12 g) in each tank (0.9 m³). Over a 7‐week feeding period, significant differences (P < 0.05) were observed on growth, FE and body mineral composition between treatments. Fish‐fed CSM‐based diets and 600 g kg^?1 SBM‐based diet had reduced growth and reduced feed and protein efficiencies when compared with those fed diet containing 300 g kg^?1 SBM or the control diet. Data from body mineral composition in response to dietary treatment could be divided into two groups. The first group refers to elements such as Mg and Fe for which carcass and fillet composition did not show significant differences with dietary level of SBM or CSM. Ca, P, K, Zn and Mn composed the second group of minerals whose concentrations in fish body were significantly reduced in fish‐fed SBM60. In conclusion, the results of this study indicate that although solvent‐extracted SBM and CSM are often reported safe for fish, they can only partially replace fish meal as a source of protein in compound feed for vundu at a limited amount between 300 and 600 g kg^?1 for SBM and <300 g kg^?1 for CSM.     

Replacing fish meal with increasing levels of meat and bone meal,soybean meal and corn gluten meal,in diets of juvenile bluegill,Lepomis macrochirus

A 60‐day study was conducted to determine the response of juvenile bluegill Lepomis macrochirus to seven experimental diets, formulated using a blend of alternative protein sources as a replacement for fish meal. Adequate levels (digestible basis) of energy, protein and amino acids were maintained in diets 1–6, whereas slightly lower protein and energy levels were provided in diet 7. Feed cost per tonne ranged from $ 798.9 (diet 1, 550 g Kg^?1 fish meal) to $ 515.8 (diet 6, 0 g kg^?1 fish meal), or to $ 507.2 (diet 7, 0 g Kg^?1 fish meal). Three commercial diets were included in the study as reference diets: a high‐energy and a low‐energy trout diet, as well as a catfish diet. Quintuplicate bluegill groups (~22 g, n = 10 fish group^?1) were fed the experimental diets twice daily to apparent satiation. No major differences in feed consumption, feed efficiency and growth rates were detected among the bluegill groups fed the experimental diets. Trout diets generally produced higher fish fat deposition, whereas the catfish diet produced a poorer fish growth rate relative to the experimental diets. Under the reported conditions, results indicate diet 6, comprising predominantly soybean meal and porcine meat and bone meal, to be the most economical diet for juvenile bluegill.     

Effect of dietary vitamin C on the growth performance,antioxidant ability and innate immunity of juvenile yellow catfish (Pelteobagrus fulvidraco Richardson)

A 12‐week feeding trial was conducted to evaluate the effects of dietary vitamin C on growth performance, antioxidant status and innate immune responses in juvenile yellow catfish, Pelteobagrus fulvidraco. Six isonitrogenous and isolipidic diets (44% crude protein and 7% lipid) were formulated to contain six graded dietary vitamin C (ascorbate‐2‐poly‐ phosphate, ROVIMIX^® STAY‐C^® 35) levels ranging from 1.9 to 316.0 mg kg^?1 diet. The results of present study indicated that fish fed the lowest vitamin C diet had lower weight gain (WG) and specific growth rate (SGR) than those fed the diets supplemented vitamin C. WG and SGR did significantly increase with dietary vitamin C levels increasing from 1.9 to 156.5 mg kg^?1. However, no significant increase was observed with further dietary vitamin C levels increasing from 156.5 to 316 mg kg^?1. Survival, protein efficiency ratio and feed efficiency were not significantly affected by the dietary vitamin C levels. The activities of serum superoxide dismutase, catalase and glutathione peroxidase significantly increased when dietary vitamin C levels increased from 1.9 to 156.5 mg kg^?1, fish fed the lowest vitamin C diet had higher serum malondialdehyde content than those fed the diets supplemented with vitamin C. Fish fed the diet containing 156.5 mg kg^?1 vitamin C had the highest lysozyme, total complement activity, phagocytosis index and respiratory burst of head kidney among all treatments. The challenge test with Aeromonas hydrophila indicated that lower cumulative survival was observed in fish fed the lowest vitamin C diet. Analysis by broken‐line regression of SGR and lysozyme activity indicated that the dietary vitamin C requirement of juvenile yellow catfish was estimated to be 114.5 and 102.5 mg kg^?1 diet, respectively.     

Immune Response and Resistance to Stress and Edwardsiella ictaluri Challenge in Channel Catfish, Ictalurus punctatus, Fed Diets Containing Commercial Whole-Cell Yeast or Yeast Subcomponents

Dietary supplementation of yeast or yeast subcomponents (YYS) as commercial preparations of β‐glucan (MacroGard^®; Biotec‐Mackzymal, Tromsø, Norway; and Betagard A^®; Aqua‐In‐Tech, Inc., Seattle, WA, USA), mannan oligosaccharide (Bio‐Mos? Aqua Grade; Alltech, Nicholasville, KY, USA), or whole‐cell Saccharomyces cerevisiae (Levucell SB20^®; Lallemand Animal Nutrition, Milwaukee, WI, USA) at the manufacturer’s recommended levels was evaluated on the physiological performance of juvenile channel catfish, Ictalurus punctatus. Fish were fed YYS diets for 4 wk, followed by 2 wk of control diet. Fish were sampled at the end of each feeding period (4 and 6 wk) to measure hematological and immune parameters and growth and to determine the effects of dietary β‐glucan on resistance to Edwardsiella ictaluri infection and to low‐water stress (6 wk). Supplementation of YYS in diets did not affect growth performance, hematology, or immune function. Survival from E. ictaluri infection was from 5 to 17.5% higher in fish fed YYS diets than in the control group, but the increases were not significant. Some improvement in stress resistance was observed in YYS‐fed catfish after exposure to low‐water stress. Stress reduction in fish fed diets supplemented with yeast subcomponents has been reported previously, but thus far, no explanation has been proposed for this effect. The present study and the previously published research suggest that dietary YYS supplementation does not appear to improve resistance of channel catfish to E. ictaluri.     

The effect of feeding diets containing deoxynivalenol contaminated corn on channel catfish (Ictalurus punctatus) challenged with Edwardsiella ictaluri

Channel catfish were fed practical corn‐soybean meal diets for 10 weeks that contained various weighed amounts of ground, dried field corn contaminated with 20 mg deoxynivalenol (DON) kg⁻¹. Weighed amounts of DON corn were blended with weighed amounts of ground, clean corn that contained no DON (0 mg kg⁻¹) to yield five diets that had 0, 2.5, 5.0, 7.5 and 10.0 mg DON kg⁻¹ of diet. Results show that catfish fed diets that contained DON for 7 weeks did not experience lower weight gains or poorer feed conversion ratios that were significantly (P > 0.05) different from control‐fed fish. Mortality of catfish during the 21‐day post‐challenge period indicate that catfish fed diets containing DON‐contaminated corn that provided at least 5.0 mg DON kg⁻¹ of diet had significantly (P < 0.05) lower mortality than catfish fed the control diet or the diet that provided 2.5 mg DON kg⁻¹ of diet. The presence of DON‐contaminated corn in the experimental diets did not significantly (P > 0.05) alter fish body weight gains and appeared to provide a protective effect for channel catfish challenged with the pathogenic bacterium Edwardsiella ictaluri.     

Aflatoxin B<Subscript>1</Subscript> (AFB<Subscript>1</Subscript>) reduces growth performance,physiological response,and disease resistance in Tra catfish (<Emphasis Type="Italic">Pangasius hypophthalmus</Emphasis>)

Triplicate groups of one hundred Tra catfish (8 g?±?0.2) were fed seven test diets containing increasing levels of AFB₁ (0, 50, 100, 250, 500, and 1000 μg AFB₁ kg^?1). Additionally Mycofix® Secure was added at 1.5% to one diet containing 500 μg AFB₁ kg^?1. Results showed that Tra catfish are sensitive to AFB₁. Reduction in weight gain (P?<?0.05) was observed for fish fed 50 μg AFB₁ kg^?1 and declined further with increasing levels of AFB₁ in the diets. Fish fed diets contaminated with 500 and 1000 μg AFB₁ kg^?1 showed increased (P?>?0.05) hepatosomatic index (HIS), while an increase in adipose somatic index (ASI) was observed in fish fed 50 μg AFB₁ kg^?1 and above when compared to the control and Mycofix® diets. After 12 weeks, blood serum analysis revealed higher alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels in fish fed the 50, 100, and 250 μg AFB₁ kg^?1 suggesting occurrence of liver damage. Disease resistance of fish exposed to Edwardsiella ictaluri was also compromised by the presence of AFB₁ in the feed and was directly related to the contamination level. Seven days after Edwardsiella ictaluri exposure, survival rates were 50, 41.7, 31.7, and 8.3% for fish fed control, 50, 100, and 250 μg AFB₁ kg^?1, respectively. This trial shows that AFB₁ at a level of 50 μg AFB₁ kg^?1 and above can affect fish performance and disease resistance. Application of an effective mycotoxin management in the feed seems to be useful to prevent the negative effects of AFB₁.     

Dietary nucleotides improve the growth performance,antioxidative capacity and intestinal morphology of turbot (Scophthalmus maximus)

A growth trial was conducted to evaluate the effects and safety of nucleotides in low fish meal diets on the growth performance, antioxidative capacity and intestinal morphology of turbot (Scophthalmus maximus). High fish meal control diet was formulated with 500 g kg^?1 fish meal. Seven levels (0.075, 0.15, 0.225, 0.300, 1.5 and 3.0 g kg^?1, respectively) of nucleotides were added to a low fish meal basal diet, which was formulated with 400 g kg^?1 fish meal. The eight experimental diets were fed to groups of juvenile turbot (initial weight: 6.0 ± 0.03 g) for 60 days. Results showed that compared with high fish meal control diet, low fish meal basal diet treatment had lower total antioxidative capacity (T‐AOC), glutathione peroxidase activity, fold height of proximal and distal intestine, enterocyte height of all evaluated enteric section and microvillus height of mid‐intestine and distal intestine (P < 0.05). However, supplemented nucleotides in diets could significantly improve growth (specific growth rate, SGR), feed utilization, antioxidative capacity and intestinal morphology of turbot (P < 0.05). Broken‐line regression analysis of SGR and T‐AOC showed that the optimal supplemental levels of dietary nucleotide for juvenile turbot were 0.366 and 0.188 g kg^?1, respectively. In summary, 0.300 g kg^?1 of dietary nucleotides was helpful in improving growth, feed utilization, antioxidative capacity and intestinal morphology of turbot fed with low fish meal diet. Excessive dietary nucleotides (3.0 g kg^?1) might cause oxidative stress and morphological damage in intestine and then reduce the growth of turbot.     

Influence of forage fish and dietary lipid supplements on egg quality and fry production in channel catfish (Ictalurus punctatus) × blue catfish (Ictalurus furcatus) hybridization

Hybrid catfish (channel catfish Ictalurus punctatus × blue catfish Ictalurus furcatus) display characteristics that are favourable to aquaculture production. Low hatch percentages are a principal reason this hybrid is not used widely in the catfish industry. This study was conducted to determine whether additional food source rich in lipids may lead to a higher quality egg production. A 10‐week feed trial was conducted in ponds in Auburn, AL. A total of 219 female Kansas Select channel catfish were stocked into nine ponds, 0.04 ha in size. Three dietary treatments were randomly allocated to the ponds. Diet‐1 was a standard 60 g kg^?1 lipid floating catfish feed. Diet‐2 was the same feed supplemented with forage fish at ～28 kg ha^?1. The third diet was the aforementioned catfish feed topcoated with 20 g kg^?1 lipid [10 g kg^?1 menhaden fish oil, 5 g kg^?1 high docosahexaenoic acid (DHA) oil and 5 g kg^?1 high arachidonic acid oil]. Results indicate that brood fish fed the high lipid diet spawned larger egg masses and had larger eggs both in weight and in diameter, with increased complements of fatty acids such as DHA, eicosapentaenoic acid and total n‐3 fatty acids. The neutral and polar lipid fractions are also presented.     

Total replacement of fish meal by soy bean meal, with various percentages of supplemental L-methionine, in diets for blue catfish, Ictalurus furcatus (Lesueur)

A 12-week feeding trial was conducted in aquaria with juvenile (8.9 g) blue catfish, Ictalurus furcatus (Lesueur), to examine effects of totally replacing fish meal with a high (65%) percentage of soy bean meal (SBM) in prepared diets. Five isonitrogenous (35% protein) and isocaloric (10.5 kJ digestible energy g^?1 of diet) diets were formulated. Diet 1 was similar to a high-quality commercial channel catfish diet, containing 15% fish meal and 42% SBM. Diets 2-5 contained 0% fish meal and 70% SBM with various amounts (0.0%. 0.3%, 0.6% and 0.9%) of L-methionine added. After 12 weeks, individual weight, weight gain, survival, specific growth rate, feed conversion ratio, protein efficiency ratio and food intake were not significantly different (P > 0.05) among treatments and averaged 36 g, 302%, 100%, 1.6% day^?1. 2.4,1.3, and 3.4% body weight, respectively. Whole-body compositions of fish were not significantly different (P > 0.05) among treatments and averaged 75%, 61% and 27% for percentage moisture, protein and fat, respectively. These data suggest that a diet with an all-plant protein source (SBM) can totally replace fish meal in a diet for blue catfish, without adverse affects on weight gain or body composition, when the dietary protein level is 35% and fish are fed to satiation.     

The growth performance of southern catfish fed diets with raw, precooked cornstarch and glucose at two levels

The ability of juvenile carnivorous southern catfish (Silurus meridionalis Chen) to use different levels, kinds and physic state (glucose, raw cornstarch and precooked cornstarch) of dietary carbohydrate was evaluated in term of growth performance. All diets contained 100 g kg^?1 lipid and 16 kJ metabolizable energy. Three isonitrogeneus (400 g kg^?1) diets were formulated to contain 150 g kg^?1 raw cornstarch, precooked cornstarch and glucose. Another three isonitrogeneus (300 g kg^?1) diets were formulated to contain 300 g kg^?1 raw cornstarch, precooked cornstarch and glucose. A control diet was formulated with no carbohydrate containing 500 g kg^?1 protein. Each experimental diet was fed to four tanks of 10 fish (28.3 ± 0.5 g) for 8 weeks at 27.5 °C. Specific growth rate (SGR) of 300 g kg^?1 glucose diet was significantly lower than those of other diets (P < 0.05). Feeding rates (FR) of 300 g kg^?1 glucose and control diets were significantly lower than those of the other diets (P < 0.05). Feed efficiency (FE) was significantly decreased with increased dietary carbohydrate level (P < 0.05). Feed efficiency of the 300 g kg^?1 glucose diet was significantly lower than those of the 300 g kg^?1 raw and precooked cornstarch diets (P < 0.05). The protein efficiency ratio (PER) was significantly increased with dietary carbohydrate level except that of the 300 g kg^?1 glucose diet, which was lowest among all diets (P < 0.05). The results suggested that both dietary starch and glucose were utilized for energy in southern catfish and had a protein‐sparing effect. At 150 g kg^?1 inclusion level, the utilization of raw and precooked cornstarch and glucose did not vary significantly, but a higher dietary glucose level (300 g kg^?1) had a markedly detrimental effect on growth in southern catfish.     

Effects of various corn distillers by‐products on growth,feed efficiency,and body composition of channel catfish,Ictalurus punctatus

A study was conducted to examine the use of corn distillers’ by‐products in diets and the effects of additional dietary fat on channel catfish, Ictalurus punctatus, performance. Juvenile channel catfish (initial weight: 12.6 g per fish) were stocked in flow‐through aquaria and fed one of six practical diets for 9 weeks. Fish fed the control + fat diet consumed more diet and had higher feed efficiency ratio (FER) than fish fed the control diet, but weight gain was not significantly different between fish fed these two diets. Fish fed the diet containing 300 g kg^?1 distillers dried grains with solubles (DDGS) consumed more diet and gained more weight, but had similar FER compared with fish fed the control + fat diet. The diet containing 200 g kg^?1 high‐protein distillers grains (HPDDG) resulted in similar diet consumption, weight gain and FER as the control + fat diet. Fish fed the diet containing 100 g kg^?1 distillers solubles (DS) consumed more diet, but had similar weight gain and FER compared with fish fed the 300 g kg^?1 DDGS diet. The presence of distillers solubles in the diet (300 g kg^?1 DDGS, 100 g kg^?1 DS, 100 g kg^?1 EDS diets) appears to increase diet consumption, weight gain, and FER over the control diets with or without additional fat.     

The effect of dietary methionine on growth,antioxidant capacity,innate immune response and disease resistance of juvenile yellow catfish (Pelteobagrus fulvidraco)

An 11‐week feeding trial was conducted to evaluate the effect of dietary methionine on the growth, antioxidant status, innate immune response and disease resistance to Aeromonas hydrophila of juvenile yellow catfish. Six isonitrogenous and isolipidic practical diets were formulated to contain different graded methionine levels ranging from 6.1 to 16.4 g kg^?1 of dry weight. The results indicated that growth performance and feed utilization were significantly influenced by the dietary methionine levels; fish fed the diet containing 6.1 g kg^?1 methionine level had lower specific growth rate, percentage weight gain (PWG), feed efficiency and protein efficiency ratio than those fed the other diets (P < 0.05). Fish fed the diet containing 16.4 g kg^?1 methionine level had lowest protein contents in whole body and muscle among all treatments. Triacylglycerols, cholesterol, aspartate aminotransferase, alanine aminotransferase and haemoglobin (Hb) in plasma or whole blood were significantly affected by dietary methionine levels. Fish fed the diet containing 6.1 g kg^?1 methionine level had higher superoxide dismutase, glutathione peroxidase activities and malondialdehyde values than those fed other diets. Fish fed diets containing 9.7 and 11.8 g kg^?1 methionine levels had higher lysozyme activity, total immune globulin, phagocytic activity and respiratory burst than those fed other diets. The lowest survival after A. hydrophila challenge was observed in fish fed a diet containing 6.1 g kg^?1 methionine. Quadratic regression analysis of PWG against dietary methionine levels indicated that the optimal dietary methionine requirement for the maximum growth of juvenile yellow catfish was estimated to be 11.5 g kg^?1 of the diet in the presence of 4.0 g kg^?1 cystine (corresponding to 23.5 g kg^?1 of dietary protein on a dry weight basis).     

Evaluation of soybean meal in the formulated diets for juvenile Pangasianodon hypophthalmus (Sauvage, 1878)

The influence of soybean meal (SBM) on the growth and feed utilization of juvenile sutchi catfish (Pangasianodon hypophthalmus, Sauvage, 1878) was investigated. Eight isonitrogenous (300 g kg^?1 CP) and isoenergetic (18 MJ kg^?1) diets were formulated incorporating Argentine SBM to replace fish meal at 0, 150, 300, 450, 600, 750, 900 and 1000 g kg^?1 dietary protein. Each diet was fed to three replicate groups of fish with an initial weight 6.0–6.2 g for twelve weeks. Growth performance decreased, and feed utilization was worsened with the increase in SBM inclusion in the diets. Final weight and relative growth rate (RGR) of fish fed control diet (0 SBM) were significantly higher than those fed test diets (P < 0.05). However, there were no significant differences in the final weight and RGR between the fish fed on 15 SBM, 30 SBM, 45 SBM and 60 SBM diets. Specific growth rate of fish fed 0 SBM, 15 SBM, 30 SBM and 45 SBM diets was significantly higher than those fed other diets. Feed conversion ratio of fish fed 0 SBM, 15 SBM, 30 SBM, 45 SBM and 60 SBM diets was significantly lower than those fed other diets (P < 0.05). The dry matter and protein digestibility were lesser in all the diets in comparison with the control diet. Hepatosomatic index and viscerosomatic index increased with increasing SBM in diet. This present trial indicated that fish meal can be replaced by SBM in the diet of juvenile sutchi catfish only up to 45% of fish meal protein without any adverse effect on growth, feed utilization and body composition.     

Optimal dietary methionine requirement of juvenile Chinese sucker,Myxocyprinus asiaticus

A total of 630 juvenile Chinese sucker, with an average initial weight of 1.72 ± 0.05 g, were fed seven diets for 56 days to study the effect of dietary methionine levels on growth, feed utilization, body composition and haematological parameters on juvenile Chinese sucker. Diet 1 using fish meal as the sole protein source and diets 2–7 using fish meal and fermented soybean meal as intact protein sources supplemented with crystalline amino acids contained six levels of l ‐methionine ranging from 6.4 to 18.9 g kg^?1 of dry diet at a constant dietary cystine level of 3.7 g kg^?1. Each diet was randomly assigned to three aquaria. Results indicated that the highest weight gain, specific growth rate (SGR), feed efficiency ratio, protein efficiency ratio and protein productive value occurred at 13.9 g methionine kg^?1 diet among the methionine supplemented dietary groups, beyond which they showed declining tendency. The whole body and muscle protein contents of juvenile Chinese sucker were positively correlated with dietary methionine level, while muscle lipid content was negatively correlated with it. The total essential amino acids content of muscle was increased significantly with increasing dietary methionine level from 6.4 to 13.9 g kg^?1 (P < 0.05). Apparent digestibility coefficients of dietary protein were significantly affected by dietary treatments. Serum protein, cholesterol and triacylglycerol increased with increasing dietary methionine levels, but showed a relatively lower value for fish fed the 18.9 g methionine kg^?1 diet. Quadratic regression analysis of SGR against dietary methionine level indicated that optimal dietary methionine requirement for juvenile Chinese sucker was 14.1 g kg^?1 of the diet in the presence of 3.7 g kg^?1 cystine (corresponding to 32.0 g kg^?1 of dietary protein on a dry‐weight basis).