Water temperature and dietary histidine affect cataract formation in Atlantic salmon (Salmo salar L.) diploid and triploid yearling smolt

The aim of the present study was to investigate cataract development in diploid (2N) and triploid (3N) Atlantic salmon smolts and post‐smolts at two water temperatures (10 and 16 °C) given diets with different histidine supplementation (LH, 10.4 and HH, 13.1 g kg^?1) before and after seawater transfer. In freshwater, a severe cataract outbreak was recorded in both ploidies reared at 16 °C. The cataract score was significantly higher in triploids compared to diploids, and the severity was lower in both ploidies fed the HH diet. The cataract development at 10 °C was minor. Low gill Na⁺, K⁺‐ATPase activity in fish reared at 16 °C before seawater transfer was followed by osmoregulatory stress with elevated plasma electrolyte concentrations and high mortality in sea water. Both diploids and triploids reared at 10 °C developed cataracts during the seawater period, with higher severities in triploids than diploids and a reduced severity in the fish fed the HH diet. The findings of this study demonstrate the importance of environmental conditions in the husbandry of Atlantic salmon, and particularly triploids, with regard to smoltification and adjusted diets to mitigate cataract development in fresh and sea water.     

Citric acid substituted the inclusion of inorganic phosphorus in diet of rainbow trout (Oncorhynchus mykiss)

This study was conducted to evaluate the effects of citric acid (CA) supplementation in diet without inorganic phosphorus (P) on growth, muscle and bone composition, proteolytic activities and serum antioxidant property of rainbow trout. Six diets were designed as the negative diet without monocalcium phosphate (MCP) supplementation, the positive diet containing 10 g kg^?1 MCP and CA supplementation diets with 4, 8, 12, 16 g kg^?1 CA supplementation in negative diet, and then were fed to rainbow trout (113.6 g) for 60 days. Results showed that the fish fed 8 g kg^?1 CA, 12 g kg^?1 CA diet had higher weight gain, higher contents of crude ash and P in bone, and lower feed conversion ratio than those of fish fed negative diet (P < 0.05), and showed the similar levels as those of fish fed positive diet (P > 0.05). The proximate composition and P level of muscle were not affected by dietary CA and MCP. The proteolytic activity in intestine, but not in stomach and gastric digesta, was significantly improved by dietary CA and MCP (P < 0.05), when compared with negative control. The activities of serum superoxide dismutase of 12 g kg^?1 CA and 10 g kg^?1 MCP groups were significantly higher, and the malondialdehyde of 8 g kg^?1 CA and 12 CA g kg^?1 groups were significantly lower than those of negative control (P < 0.05). The above results indicated that the supplementation of CA could substitute the inclusion of MCP in rainbow trout diet and the supplementation level was suggested to be 8–12 g kg^?1.     

Supplementation of dietary minerals during the early seawater phase increase vertebral strength and reduce the prevalence of vertebral deformities in fast-growing under-yearling Atlantic salmon (Salmo salar L.) smolt

An earlier study demonstrated that under‐yearling (0+) Atlantic salmon (Salmo salar L.) smolt had a lower vertebral mineral content and mechanical strength and higher prevalence of vertebral deformities than 1+ smolt during the early seawater (SW) phase. The present study aimed to examine if commercial extruded high‐energy diets need to be supplemented additional minerals for proper bone mineralization and prevention of bone deformities in fast growing 0 + smolts. We studied vertebral morphology with radiology, and bone mineral content and mechanical strength in 60 g 0+ smolt fed diets with a normal (NM) or elevated (HM) bone mineral (P and Ca) contents from SW transfer (week 0) until 10 times weight increase at week 17. Thereafter, both groups were fed a commercial diet until a mean slaughter weight of 4100 g after 57 week. There were no differences in body weight and length between the dietary groups during the study, while the condition factor differed significantly at the final sampling (NM 1.40; HM 1.29). The most common bone deformity observed was compressions in the tail region of the vertebral column. Lower incidences of vertebral deformities (percent individuals with one or more deformed vertebrae) was observed in the HM group in week 17 (HM 20%; NM 47%) and week 57 (HM 37%; NM 73%), also reflected by higher vertebral length/dorso‐ventral diameter ratio in weeks 17 (HM 0.99; MN 0.92) and 57 (HM 0.97; NM 0.88). The HM group had significantly higher vertebral mineral content (HM 550 g kg^?1; NM 480 g kg^?1) and mechanical strength (HM 9050 g mm^?1; NM 4600 g mm^?1) than the NM group after 8 week feeding. Plasma levels of Ca, P and D‐vitamin metabolites recorded in week 8 reflected changes in P homeostasis, but could not explain the preventive effect of the HM diet on development of bone deformities. The results suggest that elevated dietary mineral content during the early SW phase may reduce the prevalence of vertebral deformities in fast growing 0 + salmon smolts.     

Adult triploid Atlantic salmon (Salmo salar) have higher dietary histidine requirements to prevent cataract development in seawater

The study investigated cataract preventive effects of dietary histidine (His) supplementation in triploid Atlantic salmon during seawater grow‐out. Groups of individually PIT tagged diploid (2N) and triploid (3N) postsmolts were fed one of two supplemented dietary histidine levels; low (L, 12.6 g kg^?1 diet) or high (H, 17.4 g kg^?1 diet) from March to September following their first sea winter. Low severity cataracts were detected in both ploidy prior to supplemented His diet application. Thereafter, 3N‐L showed progression of cataract development in the second spring‐summer period, while development was inhibited in 3N‐H. Severity of cataract showed a strong family effect. A positive correlation between initial triploid seawater growth (weight and TGC) under increasing water temperature and cataract severity was identified as a major risk factor. The relationship was reversed at harvest, where triploids were on average 7.5% smaller than their diploid siblings. Lens N‐acetyl‐histidine content reflected dietary His inclusion level and cataract severity, although no significant differences in lens His content were evident between ploidy or dietary groups. Results indicate that triploid Atlantic salmon appear to have a higher dietary histidine requirement than diploids and that preventative measures can be taken to mitigate further cataract development.     

Effects of temperature on feed intake and plasma chemistry after exhaustive exercise in triploid brown trout (<Emphasis Type="Italic">Salmo trutta</Emphasis> L)

The physiological effect of temperature on feed intake and haematological parameters after exhaustive swimming in diploid and triploid brown trout (Salmo trutta) was investigated. Trout were exposed to an incremental temperature challenge (2 °C/day) from ambient (6 °C) to either 10 or 19 °C. Feed intake profiles did not differ between ploidy at 10 °C; however, triploids had a significantly higher total feed intake at 19 °C. After 24 days, each temperature–ploidy group was exposed to exhaustive swimming for 10 min. The haematological response differed between ploidy, with the magnitude of the response affected by temperature and ploidy. Post-exercise, acid–base and ionic differences were observed. Plasma lactate increased significantly from rest for both temperature and ploidy groups, but glucose increased significantly at higher temperature. Post-exercise, triploids at 19 °C had significantly higher osmolality and cholesterol than diploids, but differences were resumed within 4 h. Elevated alkaline phosphatase (ALP) and aspartate aminotransferase (AST) in fish at higher temperature suggested greater tissue damage; however, both ploidy responded similarly. Despite no significant differences in deformity prevalence, the type and location of deformities observed differed between ploidy (decreased intervertebral space with higher prevalence in tail area and fin regions for diploids, while vertebral compression, fusion in cranial and caudal trunks for triploids). These results suggest triploids have greater appetite than diploids at elevated temperature and that triploids suffer similar blood disturbances after exercise as diploids. These findings have implications for the management of freshwater ecosystems and suggest that stocking triploid brown trout may offer an alternative to diploid brown trout.     

Optimization of phosphorus content in high plant protein practical diets for Senegalese sole (Solea senegalensis,Kaup 1858) juveniles: influence on growth performance and composition of whole body and vertebrae

Practical diets containing PP sources were elaborated. Increasing levels of di‐calcium phosphate were added to diets leading to five different dietary available P levels: 2.5, 3.2, 6.0, 6.5 and 8.0 g kg^?1 dry diet. The dietary treatments were tested in 13.5 g Senegalese sole juveniles throughout an 82‐day experimental period. Dietary P content had no effect on the productive parameters, while nutrient intake was also similar among dietary treatments, except P intake. Dry matter ADC ranged between 54.9% and 64.0%, and the highest P ADCs value (47.2 ± 0.7%) was achieved in fish fed AP6.0. Dietary phosphorus level significantly influenced body lipid and P compositions. Regression analysis performed on whole‐body P and ash contents fitted to quadratic models. Vertebral bone P content was low but increased significantly with increasing dietary P levels. Bone density and deformities occurrence were, however, similar between experimental conditions. An altered status of bone formation–resorption processes in soles fed the lowest P content diet might be inferred from ALP and TRAP activities. In conclusion, overall results state a high tolerance of Senegalese sole to low P content diets and support the utilization of practical diets with high plant protein content.     

Hemoglobin level,metabolic rate,opercular abduction rate and swimming efficiency in female triploid brook trout (Salvelinus fontinalis)

Metabolic (oxygen consumption) rate, opercular abduction rate and tail beat frequency were determined in two strains of diploid and triploid female brook trout (Salvelinus fontinalis) while these fish swam at 0.37±0.02 body lengths per sec in a Blazka respirometer. Total blood hemoglobin level was also measured and opercular condition examined. Total blood hemoglobin levels in diploids and triploids were equal. The opercular abduction rate was the same in diploids and triploids (regardless of whether triploid opercular condition was good or poor) yet triploids had a lower oxygen consumption rate than diploids, indicating that triploids take up less oxygen than diploids per opercular cycle. Tail beat frequency, an indicator of swimming effort, was the same in diploids and triploids, suggesting that triploids require less oxygen than diploids for a similar swimming effort.     

Comparative performance of growth,vertebral structure and muscle composition in diploid and triploid Paralichthys olivaceus

Growth, skeletal structure and muscle composition of cold‐shock‐induced triploid olive flounder Paralichthys olivaceus were investigated. The average values of total length and total weight of triploids were higher than those of diploids from 5 to 11 months posthatch (mph). The growth difference disappeared after 11 mph. The skeletal structure of flounder at 11 mph was observed by X‐ray imaging method. There are four kinds of vertebral deformity including vertebrae fusion, one‐sided compression, two‐sided compression and vertically shifted. The trunk region (V8–18) and tailing end of the vertebral column were the predominant locations of deformity. In general, the frequencies of vertebral deformities in triploids (60.0%) were higher than those in diploids (33.3%, p < 0.05). Both the number of fish with deformed vertebrae and the average frequencies of deformed vertebrae in triploids were significantly higher than those in diploids (p < 0.05). The muscle tissues of diploid and triploid flounder at 11 mph contain the same types of fatty acid and free amino acid profiles. The number of fatty acids with significant higher contents in diploids and triploids was one and ten, respectively (p < 0.05). The contents of free amino acids showed no difference between triploid and diploid fish.     

Growth,feed utilization and body composition of juvenile Manchurian trout,Brachymystax lenok (Pallas) fed different dietary protein and lipid levels

A 10‐week feeding trial with four dietary protein levels (400, 450, 500 and 550 g kg^?1 crude protein) and two dietary lipid levels (80 and 160 g kg^?1 crude lipid) was conducted to assess optimum dietary protein and lipid levels for the growth, feed utilization and body composition of juvenile Manchurian trout (initial weight 11.80 ± 0.15 g). Fish were fed twice daily (08:30 and 16:30 h) to apparent satiation. The results showed that fish fed the diet with 500 g kg^?1 protein and 80 g kg^?1 lipid had the highest growth and feed efficiency. However, fish fed the diet with 450 g kg^?1 protein and 160 g kg^?1 lipid showed comparable growth to that of the fish fed diet 5 (500/80) and had higher protein efficiency ratio (PER), nitrogen retention (NR) and energy retention (ER) than other groups (P < 0.05). Growth, PER, NR and ER of fish fed the 160 g kg^?1 lipid diet was significantly higher (P < 0.05) than that of fish fed the 80 g kg^?1 lipid diet at 400 and 450 g kg^?1 protein diet, whereas these values showed an opposite trend at 500 and 550 g kg^?1 protein diet, and the lowest PER, NR and ER was found by fish fed the 400 g kg^?1 protein diet with 80 g kg^?1 lipid. Fish fed diets with 400 g kg^?1 protein had lower feed intake (FI) than that of other groups. Feed intake of fish fed 80 g kg^?1 lipid level was significantly lower than that of fish fed 160 g kg^?1 lipid diet at 400 g kg^?1 protein (P < 0.05), while no significant differences were observed at 450, 500 and 550 g kg^?1 protein‐based diets. Contrary to moisture content, lipid content of whole body and muscle increased significantly (P < 0.05) with increasing lipid levels. The results of this study indicated that the diet containing 450 g kg^?1 protein and 160 g kg^?1 lipid, with a P/E ratio of 23.68 g protein MJ^?1 would be suitable for better growth and feed utilization of juvenile Manchurian trout under the experimental conditions and design level used in this study.     

Effects of dietary calcium levels on growth and tissue mineralization in Japanese seabass,Lateolabrax japonicus

A feeding trial was conducted to investigate the effects of different levels of calcium (Ca) on growth and tissue mineralization in Japanese seabass, Lateolabrax japonicus. Six experimental diets were formulated to contain different levels of Ca (2.9, 4.2, 6.5, 7.9, 10.2 and 31.0 g kg^?1) from dietary ingredients and Ca‐lactate·5H₂O. The diets were fed to three triplicate groups of Japanese seabass (initial weight, 12.5 ± 0.0 g) for 56 days. Dietary Ca had no significant effect on survival or feed efficiency; however, the highest Ca (31.0 g kg^?1) diet significantly reduced weight gain, feeding rate and whole‐body and muscle protein and lipid contents, as well as serum Ca concentration and alkaline phosphatase activity. A significant reduction in vertebral Ca, P, Zn, Fe and Mn contents and scale Ca, P, Mg and Mn contents was observed in Japanese seabass as dietary Ca level increased. Deformed fish were primarily found in the 2.9 and 31.0 g Ca kg^?1 groups, indicating that these fish had poor bone mineralization.     

Comparative growth performances of diploid and triploid Chinese shrimp Fenneropenaeus chinensis (Osbeck, 1765) under different salinities

This study aimed at evaluating the ploidy effects on growth performances of Chinese shrimp ( Fenneropenaeus chinensis Osbeck, 1765) reared in different salinities under laboratory conditions. In the acute salinity experiment, there was no difference ( P >0.05) in tolerance observed in triploid and diploid shrimp due to abrupt salinity changes. The lethal salinity for 50% of the individuals in 96 h at 23–25 °C was about 2 g L⁻¹ in both triploids and diploids. While for the chronic salinity experiment, statistical analyses confirmed that the differences in growth performances including the specific growth rate (SGR), the feeding rate (FR), feed conversion efficiency (FCE) and intermoult period (IP) between triploid and diploid were related to salinity. Diploid shrimp reared in 20 g L⁻¹ exhibited highest SGR ( P <0.05), while triploids performed well in 20 and 30 g L⁻¹ salinities ( P <0.05). Based on the survival and growth data, the optimal salinity for the culture of diploid F. chinensis should be 20 g L⁻¹ and for triploids it should be between 20 and 30 g L⁻¹.     

Evaluation of dietary inclusion of housefly maggot (Musca domestica) meal on growth,fillet composition and physiological responses for barramundi,Lates calcarifer

The study was to evaluate the effects of dietary fish meal (FM) partially replaced by housefly maggot meal (HMM) on growth, fillet composition and physiological responses of juvenile barramundi, Lates calcarifera. HMM at 100, 150, 200 and 300 g kg^?1 was supplemented in the basal diet to replace dietary FM protein. Basal diet without HMM supplementation was used as control. Total of five experimental diets were fed to triplicate groups of juvenile barramundi (initial weight: 9.66 ± 0.22 g) in a flow‐through rearing system for 8 weeks. Fish fed all experimental diets showed no effects (P > 0.05) on weight gain and whole body protein, lipid and moisture content. Fish fed control diet and 100 g kg^?1 HMM diet had the highest (P < 0.05) hepatic superoxide dismutase (SOD) activity, followed by 150 g kg^?1 HMM group, the lowest in 200 and 200 g kg^?1 HMM groups. Hepatic thiobarbituric acid reactive substance (TBARS) value was the highest in fish fed 150–300 g kg^?1 HMM diets, followed by 100 g kg^?1 HMM group and the lowest in fish fed the control diet. Fish fed the 300 g kg^?1 HMM diet had lower plasma lysozyme activity than fish fed other diets. The results indicated that up to 300 g kg^?1 HMM can be used to substitute dietary FM protein without negative effect on growth. Although physiological responses were also considered, up to 100 g kg^?1 HMM in barramundi diet was recommended.     

Use of probiotics to enhance growth,stimulate immunity and confer disease resistance to Aeromonas salmonicida in rainbow trout (Oncorhynchus mykiss)

An 8‐week feeding trial was conducted to evaluate the effects of dietary probiotics on growth, non‐specific immune responses and disease resistance in juvenile rainbow trout, Oncorhynchus mykiss. Fish averaging 5.8 ± 0.8 g (mean ± SD) were fed one of the five experimental diets; one control (Cont), and four other diets were prepared by supplementing single probiotics 1 (Bacillus subtilis; SP₁, 0.5%), single probiotics 2 (Bacillus licheniformis; SP₂, 0.5%), multi‐probiotics (B. subtilis + B. licheniformis; MP, 0.5%) and oxytetracycline (OTC) at 5 g OTC kg^?1 diet. After 8 weeks of the feeding trial, weight gain and specific growth rate of fish fed SP₁, SP₂ and OTC diets were significantly higher than those of fish fed Cont diet (P < 0.05). Superoxide dismutase (SOD) and lysozyme activities of fish fed SP₁, SP₂ and MP diets were significantly higher than those of fish fed Cont diet (P < 0.05). There were no significant differences in SOD and lysozyme activities among fish fed SP₁, SP₂, MP and OTC diets. In challenge test with Aeromonas salmonicida for 15 days, fish fed SP₁, SP₂ and MP diets showed significantly higher cumulative survival rate than those of fish fed Cont diet (P < 0.05). However, there were no significant differences in cumulative survival rate among fish fed SP₁, SP₂, MP and OTC diets. Although there was a little advantage in fish fed MP diet in terms of non‐specific immune responses, single or multi‐probiotics are equally effective statistically. These results indicate that single or multi‐probiotics had equal beneficial effects as an antibiotic replacer on growth performance, non‐specific immune responses and disease resistance in juvenile rainbow trout.     

The prevalence of vertebral deformities is increased with higher egg incubation temperatures and triploidy in Atlantic salmon Salmo salar L.

Suboptimal egg incubation temperature is a risk factor for the development of skeletal deformities in teleosts. Triplicate diploid and triploid Atlantic salmon, Salmo salar L., egg batches were incubated at 6, 8 and 10 °C up until first feeding, whereupon fish were reared on a natural temperature before examination for externally visible skeletal deformities (jaw and spine) and radiographed for vertebral deformities and morphology at the parr stage. Increasing incubation temperatures and triploidy increased the number of fish showing one or more deformed vertebrae. Triploids had significantly higher mean vertebrae cranio‐caudal length (L) and dorsal‐ventral height (H) ratio at 6 and 10 °C than diploids, but triploidy had no effect on mean vertebrae centra area. Triploids demonstrated an increase in lower jaw deformities with increased incubation temperature, whereas jaw deformities were rare in diploids. Fish incubated at 10 °C had a significantly lower mean vertebral number than fish incubated at 6 °C, and triploids had lower mean vertebral numbers than diploids. Diploid fish with 58 vertebrae had a significantly higher mean vertebral centra area than fish with 59 vertebrae, but vertebral number did not affect the mean vertebral L/H ratio. The results are discussed with respect to the welfare and production of farmed salmonids.     

Effects of dietary mannan oligosaccharide on growth,survival, physiological,immunological and gut morphological conditions of black tiger prawn (Penaeus monodon Fabricius 1798)

The aim of this experiment was to determine the effects of dietary inclusion with mannan oligosaccharide (Bio‐Mos, Alltech, Nicholasville, KY, USA) on growth, survival, physiological and immunological conditions and gut morphology of the black tiger prawn (Penaeus monodon). Five diets supplemented with MOS at 0 g kg^?1 (control diet), 1, 2, 4 and 8 g kg^?1 were fed to the prawn juveniles (0.4 ± 0.06 g, total weight) for the duration of 63 days. Growth was the highest (P < 0.05) when the prawns were fed the 1 g kg^?1 MOS included diet. Wet tail muscle index (Tw/B), dry tail muscle index (Td/B) and tail muscle protein (Tmp) were higher (P < 0.05) in the prawns fed MOS included diets MOS compared with the prawns fed the control diet. Total haemocyte counts (THCs) of the prawns fed MOS included diets were higher (P < 0.05) than THCs of the prawns fed the control diet. Epithelium layer and epidermal cell density of the gut of the prawns fed 1 g kg^?1 and 2 g kg^?1 MOS diets were better than the prawns fed the control and other MOS diets. The results imply a positive effect of dietary supplementation of 1–2 g kg^?1 MOS in the culture of black tiger prawns.     

Growth and Survival of Intrastrain and Interstrain Rainbow Trout (Oncorhynchus mykiss) Triploids1

Triploid rainbow trout exhibit improved survival and extended growth during sexual maturation, compared to their diploid counterparts. However, there have been few benefits demonstrated prior to sexual maturation. This study was undertaken to investigate the possibility of improving growth and survival parameters in triploids through interstrain crosses. Triploids were induced by heat shocking fertilized eggs from intra- and interstrain crosses of two rainbow trout strains. The four triploid groups and their diploid counterpart groups were reared to 233 days post-hatching and analyzed for growth and survival characteristics. Compared with diploids, triploids had significantly (P < 0.05) higher mortalities during the first 100 days post-fertilization, primarily just prior to and after hatching. However, during the remainder of the study triploids exhibited significantly (P < 0.05) lower mortalities than diploids. During the first 50 days of rearing all four triploid groups were significantly shorter and lighter than their diploid counterparts. The growth of the triploid groups later in the study varied considerably. At the conclusion of the rearing phase, one interstrain triploid group was significantly (P < 0.05) longer than its diploid counterpart, although not significantly heavier. The other triploid groups were either significantly smaller than, or equal to the diploids. Analysis of variance indicated that the growth of triploid rainbow trout was significantly affected by maternal strain effects. These results suggest that the use of specific strains and crosses may improve the growth of triploid rainbow trout.     

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).     

A comparison of the effect of dietary fungal phytase and dicalcium phosphate supplementation on growth performances,feed and phosphorus utilization of tra catfish juveniles (Pangasianodon hypophthalmus Sauvage, 1878)

Six isonitrogenous (320 g kg^?1) and isolipidic (60 g kg^?1) diets were formulated with graded levels (0, 5, 10 and 15 g kg^?1) of dicalcium phosphate (DCP) and fungal phytase (750 and 1500 FTU kg^?1 diet). Tra catfish (Pangasianodon hypophthalmus), 9.6 g, were fed the diets for 12 weeks. Each experimental diet was fed to eight replicates of fish to apparent satiation. At the end of the trial, fish fed the diets containing 15 g kg^?1 DCP, 750 and 1500 FTU kg^?1 phytase had higher growth performances, protein efficiency ratio and phosphorus retention than those fed the control diet, 5 g kg^?1 DCP and 10 g kg^?1 DCP diets (P < 0.05). Whole body ash and phosphorus concentration of fish fed the 10 g kg^?1 DCP and 15 g kg^?1 DCP diets were significantly higher than those of fish fed the control diet. Higher apparent digestibility coefficient of phosphorus was observed in fish fed the phytase supplemented diets. The present results indicate that supplementation of phytase at 750 FTU kg^?1 and 1500 FTU kg^?1 improves growth performances, feed and phosphorus utilization. The supplementation can completely replace dicalcium phosphate or other phosphorus sources in tra catfish feed and reduce the phosphorus discharge into environment.     

Effect of dietary lipid and protein levels with different protein to energy ratios on growth performance,feed utilization and body composition of Rutilus frisii kutum (Kamenskii, 1901) fingerlings

A 3 × 5 factorial design including three lipid levels (100, 130 and 180 g kg^?1 diet, based on dry matter) and five dietary protein levels (370, 420, 470, 520 and 570 g kg^?1 diet, based on dry matter) was conducted to investigate the optimum dietary lipid and protein requirements for Rutilus frisii kutum fingerlings. Triplicate groups of 80 kutum (500 ± 60 mg initial weight) were stocked in 250‐l tanks and fed to apparent satiation thrice daily for 8 weeks. The results showed that the growth performance and feed utilization were significantly (P < 0.05) affected by dietary protein and lipid levels. Weight gain, specific growth rate and feed conversion ratio of kutum improved significantly with increasing protein level from 370 to 470 g protein kg^?1 diet, but there was a significant decrease in growth parameters with increasing protein level from 470 to 570 g protein kg^?1 diet. Also, the higher values of weight gain, specific growth rate and better feed conversion ratio were observed for fish fed diets containing 130 g kg^?1 lipid diet. The results of this study showed that diet containing 420 g kg^?1 protein and 130 g kg^?1 lipid with a P:E ratio of 19.22 mg protein kJ^?1 of gross energy is optimal for kutum fingerlings.