Optimum feeding rates in juvenile olive flounder,Paralichthys olivaceus,at the optimum rearing temperature

Two feeding trials were carried out to determine the optimum feeding rates in juvenile olive flounder, Paralichthys olivaceus, at the optimum rearing temperature. Fish averaging 5.0 ± 0.11 g (mean ± SD) in experiment 1 and 20.2 ± 0.54 g (mean ± SD) in experiment 2 were fed a commercial diet at the feeding rates of 0%, 3.0%, 4.0%, 4.25%, 4.5% and 4.75% body weight (BW) day^?1 and satiation (5.52% BW day^?1) in experiment 1 and 0%, 1.0%, 2.0%, 3.0% and 3.5% BW day^?1 and satiation (4.12% BW day^?1) in experiment 2 at 20 ± 1 °C. Both feeding trials lasted for 2 weeks. Results from experiment 1 indicated that weight gain (WG) and specific growth rate (SGR) of fish fed to satiation were significantly higher than those of fish fed at other feeding rates while feed efficiency (FE) and protein efficiency ratio (PER) of fish fed at 4.25% BW day^?1 were significantly higher than those of fish fed to satiation and fish fed at 3.0% BW day^?1 (P < 0.05). In experiment 2 WG, SGR and PER leveled out after the feeding rate of 3.5% BW day^?1 whereas FE reached a plateau at 3.0% BW day^?1. anova of FE indicated that the optimum feeding rates in 5.0 and 20 g juvenile olive flounder could be 4.25% and 3.0% BW day^?1, respectively. Broken line analysis of WG suggested the optimum feeding rates of 5.17% and 3.47% BW day^?1 in 5.0 and 20 g fish, respectively. Therefore, these results indicated that the optimum feeding rates could be >4.25 but <5.17% BW day^?1 for 5.0 g, and it could be >3.0 but <3.47% BW day^?1 for 20 g size of juvenile olive flounder at the optimum rearing temperature.     

Utilization of diets with different fish oil content in common octopus (Octopus vulgaris Cuvier, 1797) and resulting changes in its biochemical composition

The aim of the present work was to obtain the lipid utilization of Octopus vulgaris supplying formulated semi‐moist diets with different contents in cod oil (reduced from water content): 0 g kg^?1 (A0, 138 g kg^?1 lipids DW; N = 4), 100 g kg^?1 (A100, 286 g kg^?1 lipids DW; N = 6) and 200 g kg^?1 (A200, 388 g kg^?1 lipids DW; N = 6). The rest of the ingredients were constant in the three diets: 200 g kg^?1 gelatin, 100 g kg^?1 egg yolk powder, 150 g kg^?1 freeze‐dried Todarodes sagittatus and 50 g kg^?1 freeze‐dried Sardinella aurita). Survival was 100% with the three diets. The highest absolute feeding (15.8 ± 1.2 g day^?1), growth (9.6 ± 1.4 g day^?1; 0.91% BW day^?1) and feed efficiency rates (60.3%) were obtained with diet A0. This diet also showed greater retention of lipid and protein than A100 and A200. Protein digestibility was above 95% in all of the diets. Only diet A0 led to a high lipid digestibility coefficient (81.25%), which fell drastically to 12.3% in A200. It was notable the high polar lipid digestibility rates (83–89%) respect to neutral lipids (2–87%) in all diets. The best results were obtained with lipid feeding rates of around 1 g day^?1 and a suitable lipid content on 130–140 g kg^?1 DW in formulated diets for O. vulgaris.     

Evaluation of feeding rate based on growth,feed conversion,protein gain and carcass quality of fingerling Indian major carp,Catla catla (Hamilton)

The effects of feeding rates on growth, feed conversion, protein deposition and carcass quality of fingerling Catla catla (3.61 ± 0.03 cm; 0.71 ± 0.04 g) were worked out by conducting a 16‐week feeding trial. Fingerlings were fed with a casein‐gelatin‐based purified diet (40% crude protein CP; 14.95 MJ kg^?1 digestible energy; DE) at 1%, 2%, 3%, 4%, 5%, 6% and 7% body weight per day. The absolute weight gain (AWG; 10.50 g fish^?1) and feed conversion ratio (FCR; 1.41) were highest at the feeding rate of 5% body weight per day. However, protein gain (PG; 0.36 g fish^?1) and carcass protein content attained the maximum values at 4% BW day^?1. Quadratic regression analyses of AWG g fish^?1 and PG g fish^?1 at 95% maximum response indicated that these parameters attained the best values at 4.19% and 3.81% BW day^?1. On the basis of the above results it is recommended that the feeding rate in the range of 3.81–4.19% BW day^?1 with a P:E ratio of 26.69–27.74 mg protein MJ^?1 DE is optimum for maximum growth, efficient feed conversion and best carcass quality in fingerling C. catla.     

Effects of feeding rate and frequency on growth performance,digestion and nutrients balances of Atlantic salmon (Salmo salar) in recirculating aquaculture systems (RAS)

A 10‐week study was conducted to investigate the effects of feeding rate and frequency on growth performance, digestion and nutrients balances of Atlantic salmon (Salmo salar) in replicated recirculating aquaculture systems (RAS). Replicated groups of juvenile salmon weighing 90 ± 2.5 g (mean ± SD) were fed a commercial feed (21.63 MJ kg^?1 gross energy) to designed feeding rate (1.4%, 1.6% and 1.8% body weight day^?1, BW day^?1) and feeding frequency (2 and 4 meals day^?1) combinations. Specific growth ratio varied between 1.15 ± 0.02 and 1.37 ± 0.16% day^?1, and feed conversion ratio ranged from 0.96 ± 0.03 to 1.16 ± 0.02. The nitrogen and phosphorus retention rates were from 36.50 ± 1.94 to 47.08 ± 5.23% and from 20.42 ± 1.05 to 38.59 ± 2.80%. Apparent digestibility coefficients (ADC) in dry matter, protein, lipid and energy showed no significant differences for all groups. However, fish fed at 1.6% BW day^?1 and 4 meal day^?1 groups had relatively better growth and nutrient retention efficiency compared to other groups. In addition, concentrations of nitrogenous and phosphorous compounds were also detected in this study. These results suggested that salmon of 100–200 g in RAS could in practice be fed at 1.6% BW day^?1 and 4 meals day^?1, taking environmental impacts into account.     

High feeding and growth rates in common octopus (Octopus vulgaris) fed formulated feeds with an improved amino acid profile and mixture of binders

Four semi‐moist formulated feeds were supplied to Octopus vulgaris subadults (664 ± 70 g; 18.4 ± 0.7°C) in two different experiments. In the experiment #1, two diets were prepared with a new mixture of binders (gelatine 150 g kg^?1, starch 100 g kg^?1 and gum 50 g kg^?1). The GEL15‐Squid and GEL15‐Hake feeds included 100 g kg^?1 freeze‐dried squid (Todarodes sagittatus) or hake (Merluccius sp.) respectively. Both feeds showed low water disintegration rates at 24 h (13.6–15.0% dry weight). The specific feeding rate was higher in animals fed GEL15‐Hake (2.7%BW day^?1), but the growth and feed efficiency were significantly better in animals fed GEL15‐Squid (1.4%BW day^?1 and 61.2% respectively; P < 0.05). The proximate composition of the digestive gland, carcass and whole animals was similar. In the experiment #2, the GEL15‐Squid amino acid profile was improved by replacing 50 g kg^?1 gelatine by 50 g kg^?1 freeze‐dried squid (GEL10‐Squid) or freeze‐dried fish (GEL10‐Fish). These feeds showed higher water disintegration rates (31.7–36.3% dry weight). The feeding rates (2.2–2.3%BW day^?1), growth (1.5%BW day^?1) and feed efficiency were similar for both diets. Total lipids were higher in the digestive gland and whole animals fed GEL10‐Fish diet (P < 0.05). Future effort could be directed towards alternative binders that allow improve amino acid balance with a minimum gelatine content or even supplementation trials including essential amino acids.     

Dietary methionine requirement of Indian major carp fry,Cirrhinus mrigala (Hamilton) based on growth,feed conversion and nitrogen retention efficiency

This study was aimed at quantifying methionine requirement of Indian major carp fry, Cirrhinus mrigala (2.2 ± 0.2 cm; 0.19 ± 0.02 g) by conducting a 12‐week feeding trial. Casein–gelatine‐based isonitrogenous (40 g 100 g^?1 crude protein) and isoenergetic (15.42 kJ g^?1 DE) amino acid test diets were prepared to contain six levels of l ‐methionine (1.1, 1.3, 1.5, 1.7, 1.9 and 2.1 g 100 g^?1 dry diet) at a fixed level of cysteine (0.85 g 100 g^?1 dry diet) and fed to apparent satiation thrice daily to triplicate groups of fish. When absolute weight gain (g per fish), feed conversion ratio, protein deposition (g per fish) and nitrogen retention efficiency data were subjected to broken‐line and second‐degree polynomial regression analysis, 95% of the plateau of above parameters was achieved at dietary methionine concentrations between 1.60 and 1.69 g 100 g^?1 dry diet or 0.10 to 0.11 g methionine kJ^?1 DE, corresponding to 4.1–4.22 g 100 g^?1 protein or 0.44–0.47 g methionine kJ^?1 DE. Based on these results, dietary methionine requirement of fry C. mrigala is recommended 1.60–1.69 g 100 g^?1 diet or 0.10–0.11 g methionine kJ^?1 DE.     

Effects of feeding rate on growth performance and nutrient partitioning of young‐of‐the‐year white sturgeon (Acipenser transmontanus)

A 10‐week growth trial was performed to evaluate the effects of feeding rate on growth performance, nutrient partitioning, and to determine the optimum feeding rate for young‐of‐the‐year white sturgeon. Three tanks with 30 fish per tank each were assigned to five feeding rates, 0.4–2.0% body weight per day (BW day^?1). Weight gain significantly (P < 0.05) increased with increasing feeding rate up to 1.2% BW day^?1. Feed efficiency exhibited an inverse relationship to weight gain. Hepatosomatic and gonadal‐fat‐body (GFB)‐somatic indices were significantly affected by feeding rate, and the lowest values were observed at 0.4% BW day^?1. The increased feeding rate significantly affected whole‐body and carcass lipid and moisture contents. Protein gain in the carcass, but not in the GFB, was significantly influenced by feeding rate. Lipid gain in the carcass and GFB was also significantly affected by feeding rate. Four regression models were tested for the estimation of optimum feeding rate, including one‐slope straight broken‐line, two‐slope straight broken‐line, quadratic broken‐line and quadratic models. Adjusted coefficient of correlation and corrected Akaike information criterion were used to compare model performance. The quadratic broken‐line model was chosen as the best based on the criteria. The estimated optimum feeding rate for young‐of‐the‐year white sturgeon (360 g) is 1.5% BW day^?1.     

Development of low‐lipid formulated feeds with different protein/energy ratios for Octopus vulgaris ongrowing

We studied the feeding and growth rates, feed efficiency and nutritional composition of subadult octopuses (689 ± 77 g) fed low‐lipid diets with two different protein/energy ratios (P/E): Medium P/E diet (30.5 g protein MJ^?1, 662 g kg^?1 protein dry weight (dw)) or High P/E diet (36.8 g protein MJ^?1, 843 g kg^?1 protein dw). Survival was 100% for the Medium P/E and 87.5% for the High P/E diet. The specific feeding rates were 1.91% and 1.67% body weight day^?1 for the Medium P/E and High P/E diet, respectively (P < 0.05). The specific growth rates (0.92% and 1.25% body weight day^?1), feed efficiency indices (47.3% and 72.7%), productive protein value (23.9% and 29.1%) and digestive gland index (5.6% and 6.4%) were significantly better in animals fed the High P/E than the Medium P/E diet (P < 0.05). The proximate composition of the digestive gland was similar for both diets, but the total lipid content of carcass was higher in animals fed the Medium P/E diet (P < 0.05). Our results suggest that the protein content of the feed could be a factor regulating feeding rates in octopus.     

Comparative study on dietary protein requirements for juvenile and pre‐adult gibel carp (Carassius auratus gibelio var. CAS III)

Two 8‐week growth trials were conducted in indoor recirculation system to evaluate the protein requirements for juvenile (3.70 ± 0.20 g) and pre‐adult (85.2 ± 0.70 g) gibel carp, Carassius auratus gibelio var. CAS III. Six isoenergetic diets were formulated for each trial using fish meal and casein as protein sources, and protein level was 250–450 g kg^?1 in Trial 1 and 200–450 g kg^?1 in Trial 2. With the increasing dietary protein, feeding rate (FR) and feed conversion ratio (FCR) significantly decreased (P < 0.05). Weight gain (WG) increased first and then reached a plateau in 330–450 g kg^?1 in Trial 1 (P > 0.05), while decreased after the maximum value in 350 g kg^?1 in Trial 2 (P < 0.05). Productive protein values (PPVs) were lower in 370–450 g kg^?1 in Trial 1 and 400–450 g kg^?1 in Trial 2 (P < 0.05). Increasing dietary protein level increased protein content and decreased lipid content in whole fish body and white muscle (P < 0.05). Apparent digestibility coefficient of dry matters (ADC_d) decreased, while apparent digestibility coefficient of protein (ADC_p) increased in 370–450 g kg^?1 in Trial 1 and 250–450 g kg^?1 in Trial 2 (P < 0.05). Trypsin activity significantly increased in 370–450 g kg^?1 in Trial 1 (P < 0.05) and was not affected in Trial 2 (P > 0.05). Hepatic alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities in both trials increased when dietary protein was above 400 g kg^?1 (P < 0.05). Based on quadratic regression of WG, it was estimated that dietary protein requirement for maximum growth was 414 g kg^?1 (digestible protein of 376 g kg^?1) and 365 g kg^?1 (digestible protein of 324 g kg^?1) for juvenile (3.70 g) and pre‐adult gibel carp (85.2 g).     

Ambient salinity and osmoregulation,energy metabolism and growth in juvenile yellowtail kingfish (Seriola lalandi Valenciennes 1833) in a recirculating aquaculture system

The effects of salinity on plasma osmolality, branchial chloride cell density, feed consumption and conversion and growth performance of yellowtail kingfish (Seriola lalandi) were evaluated. Fish (11.6 ± 0.6 g) were kept for 29 days at 14, 18, 22, 26 (experimental) and 30 g L^?1 (control) salinity in independent, pilot‐scale recirculation aquaculture systems. No differences in plasma osmolality or chloride cell numbers in gills were observed, pointing to a strong osmoregulatory capacity in the juveniles. Fish at 14, 18 and 22 g L^?1 (7.61 ± 0.19, 7.61 ± 0.01 and 7.61 ± 0.13% day^?1, respectively) had higher growth rates than fish at 26 and 30 g L^?1 (7.10 ± 0.05 and 6.97 ± 0.06% day^?1 respectively). The higher growth rate at lower salinity resulted from increased feed intake; feed conversion was not different. An evaluation of the impact of salinity on growth rate of on‐growing stages (till market size) seems warranted to assess whether the profitable effects of low salinity persist in later stages of this important aquaculture species.     

Residue levels of enrofloxacin and ciprofloxacin in processed animal by‐products used in Atlantic salmon feeds and their long‐term carry‐over to the edible part of the fish

Residue levels of the antibacterials enrofloxacin and ciprofloxacin were analysed in 15 commercially relevant animal by‐products (ABPs). Enrofloxacin was detected in all ABPs, and ciprofloxacin was detected in 11 of 15 ABP samples. Feed to muscle and skin carry –over of low background enro‐ and ciprofloxacin levels were assessed by applying a simple toxicokinetic model. The muscle and skin uptake and elimination rates were established in Atlantic salmon (Salmo salar L.) fed enrofloxacin enriched diets (100 μg kg^?1 ‘low’ and 4000 μg kg^?1 ‘high’) in triplicate for 41 days followed by a 90 days depuration period. The terminal half‐lives were 17 ± 0.4 and 18 ± 0.7 days, and uptake rates were 9.3 ± 3.3 and 11 ± 3.1 (day^?1) for the ‘low’ and ‘high’ groups, respectively. Only fish fed high background levels had quantifiable levels of the metabolite ciprofloxacin with a formation of 0.25 ± 0.01% day^?1. The toxicokinetic carry‐over model predicted muscle and skin steady state levels of 1.8 μg kg^?1 when fed theoretically high enrofloxacin levels (158 μg kg^?1), which is below the EU limit of 100 μg kg^?1 for enrofloxacin in finfish food products. The antibacterial residue levels could however be detected in EU food surveillance programmes.     

Effective use of glucose rather than starch in formulated semimoist diets of common octopus (Octopus vulgaris)

The aim of the present work was to test the capacity of Octopus vulgaris to use carbohydrates supplied in three diets: a diet without added carbohydrates (diet C0: 500 g kg^?1 water, 200 g kg^?1 gelatine, 100 g kg^?1 egg yolk powder, 50 g kg^?1 freeze‐dried Sardinella aurita and 150 g kg^?1 freeze‐dried Todarodes sagittatus) and two obtained by substituting 50 g kg^?1 of T. sagittatus by glucose (diet GLU50) or by starch (diet STA50). The most stable and best‐accepted diet was STA50 (SFR 1.26%BW day^?1) although there were no significant differences in the growth rates obtained with the three diets: 10.12 g day^?1, 9.37 g day^?1 and 11.22 g day^?1 for C0, GLU50 and STA50, respectively (P > 0.05). The feed efficiency indices were better for GLU50, of particular note being the protein productive value of 71.88% and a feed conversion ratio lower than 1. Protein and lipid digestibility were similar in all the three diets (96–98% for proteins and 85–94% for lipids), whereas carbohydrate digestibility was higher in GLU50 (98%) than in C0 (84%) and STA50 (0.33%). The content of carbohydrates increased in muscle and the digestive gland as a consequence of the increased carbohydrates intake.     

Removal of nitrogen by Algal Turf Scrubber Technology in recirculating aquaculture system

Ongoing research in recirculation aquaculture focuses on evaluating and improving the purification potential of different types of filters. Algal Turf Scrubber (ATS) are special as they combine sedimentation and biofiltration. An ATS was subjected to high nutrient loads of catfish effluent to examine the effect of total suspended solids (TSS), sludge accumulation and nutrient loading rate on total ammonia nitrogen (TAN), nitrite and nitrate removal. Nutrient removal rates were not affected at TSS concentration of up to 0.08 g L^?1 (P > 0.05). TAN removal rate was higher (0.656 ± 0.088 g m^?² day^?1 TAN) in young biofilm than (0.302 ± 0.098 g m^?² day^?1 TAN) in mature biofilm at loading rates of 3.81 and 3.76 g m^?² day^?1 TAN (P < 0.05), respectively, which were considered close to maximum loading. TAN removal increased with TAN loading, which increased with hydraulic loading rate. There was no significant difference in removal rate for both nitrite and nitrate between young and mature biofilms (P > 0.05). The ATS ably removed nitrogen at high rates from catfish effluent at high loading rates. ATS‐based nitrogen removal exhibits high potential for use with high feed loads in intensive aquaculture.     

Effects of dietary protein and lipid levels on growth, feed conversion and body composition in rohu, Labeo rohita (Hamilton), fingerlings

Twelve experimental diets (D‐1 to D‐12) in a 4 × 3 factorial design (four protein levels: 250, 350, 400 and 450 g kg^?1 and three lipid levels: 50, 100 and 150 g kg^?1) were formulated. Carbohydrate level was constant at 250 g kg^?1. Rohu fingerlings (average wt. 4.3 ± 0.02 g) were fed the experimental diets for 60 days in three replicates at 2% BW  day^?1. Weight gain (%), specific growth rate (% day^?1) and feed gain ratio (FGR) indicated that diets containing 450 g kg^?1 protein and 100 or 150 g kg^?1 lipid (diets D‐11 and D‐12) resulted in best performance, although results were not significantly different from those of diet D‐9 (400 g kg^?1 protein and 150 g kg^?1 lipid). Protein efficiency ratio was highest with diets D‐6 (350 g kg^?1 protein and 150 g kg^?1 lipid) and D‐9 (400 g kg^?1 protein and 150 g kg^?1 lipid) (P > 0.05) and declined with higher and lower protein diets at all levels of lipid tested. Elevated lipid level (50, 100 or 150 g kg^?1) did not produce better FGR in diets containing 400 and 450 g kg^?1 dietary protein (P > 0.05). The combined effects of protein and lipid were evident up to 400 g kg^?1 protein. Growth and FGR showed consistent improvement with increased lipid levels from 50 to 150 g kg^?1 at each protein level tested except with diets containing 450 g kg^?1 protein. Apparent nutrient digestibility (for protein, lipid and energy) did not show significant variation among different dietary groups (P > 0.05). Whole body protein and lipid contents increased significantly (P > 0.05) with dietary protein level. The results of this study indicate that rohu fingerlings are adapted to utilize high protein in diets with varying efficiency. The fish could utilize lipid to spare protein but there is no significant advantage from this beyond the dietary protein level of 350–400 g kg^?1 in terms of growth and body composition.     

Effective use of glucose rather than starch in formulated semimoist diets of common octopus (Octopus vulgaris)

The aim of the present work was to test the capacity of O. vulgaris to use carbohydrates supplied in three diets: a diet without added carbohydrates (diet C0: 500 g kg^?1 water, 200 g kg^?1 gelatine, 100 g kg^?1 egg yolk powder, 50 g kg^?1 freeze‐dried Sardinella aurita and 150 g kg^?1 freeze‐dried Todarodes sagittatus), and two obtained by substituting 50 g kg^?1 of T. sagittatus by glucose (diet GLU50) or by starch (diet STA50). The most stable and best accepted diet was STA50 (SFR 1.26%BW day^?1), although there were no significant differences in the growth rates obtained with the three diets: 10.1 g day^?1, 9.4 g day^?1 and 11.2 g day^?1 for C0, GLU50 and STA50, respectively (P > 0.05). The feed efficiency indices were better for GLU50, of particular note being the protein productive value of 72% and a feed conversion ratio lower than 1. Protein and lipid digestibility were similar in all three diets (96–98% for proteins and 85–94% for lipids), whereas carbohydrate digestibility was higher in GLU50 (98%) than in C0 (84%) and STA50 (0.33%). The content of carbohydrates increased in muscle and the digestive gland as a consequence of the increased carbohydrates intake.     

The effects of water temperature and stocking density on survival,feeding and growth of the juveniles of the hybrid yellow catfish from Pelteobagrus fulvidraco (♀) × Pelteobagrus vachelli (♂)

In this study, we aimed to investigate the effects of water temperature and stocking density on the survival, feeding and growth of the juveniles of the hybrid yellow catfish from Pelteobagrus fulvidraco (♀) × Pelteobagrus vachelli (♂) using the parameters as follows: survival rate (%), feeding rate (% day^?1), feed conversion ratio, specific growth rate (% day^?1), coefficient of variation (%), productivity (P, g m^?3 day^?1) and condition factor. We reared the juvenile fish (3.25 ± 0.21 g) at 12 water temperature levels and six stocking density levels (each level included three aquaria in two batches of experiments). The results showed that all groups survived at a temperature range of ≤35°C during a 46‐day experimental period, and they could achieve a high growth at a water temperature range of 26–32°C. The optimal temperature for growth was 29.8°C. Productivity peaked at a stocking density of 1.9 kg m^?3. Our results indicated that the hybrid is very suitable for commercial aquaculture.     

Performance of formulated diets with different level of lipids and glutamate supplementation in Octopus vulgaris

Growth, feed efficiency and proximate and lipid class composition of subadults Octopus vulgaris (788 ± 133 g; 18.5°C) fed formulated diets of low lipid (LL: 8 g kg^?1) and high lipid levels (HL: 84 g kg^?1) and each one of these with three different levels of glutamate supplementation (0, 5 and 20 g kg^?1) were compared. All the animals accepted the diets with a survival of 100%. The addition of glutamate did not stimulate feeding rates in any of the assays (2.48–2.64 and 1.86–2.01%Body weight day^?1 for LL and HL, respectively; P > 0.05). The best growth, feed efficiency and protein productive value were observed in the groups fed 5 or 20 g kg^?1 glutamate supplementation at both lipid levels, with significant differences for LL diet (P < 0.05). A better feed efficiency was achieved with the HL diet (14.6–27.5% vs. 2.5–19.2% for LL diet). There were no significant differences in the proximate composition of carcass (animal excluding the digestive gland). However, a substantial amount of lipids accumulated in the digestive gland, mainly triglycerides, was detected as a consequence of higher lipid ingestion or glutamate supplementation. It was notable the lower percentages of phosphatidylethanolamine and phosphatidylcholine in the digestive gland of animals with best growth.     

Increasing growth and feed efficiency of Juvenile Walleye,Sander vitreus (Mitchill, 1818), through novel,subsatiation, restrict/feed cycles from late summer into fall

The role of restricted feeding on the growth and feed efficiency (FE) of juvenile walleye, Sander vitreus, was investigated through two experiments. In the summer/fall experiment, 7.44‐g walleye were fed on one of the three schedules for 84 days: control (daily satiation feeding at 6% BW day^?1), D2 (2 days of feed deprivation, then fed at 12% BW day^?1 for 7 days, repeated throughout the study) and SS80 (subsatiation feeding involving 2 weeks of maintenance ration, then fed at 80% of the control group's feeding level). Juvenile walleye growth rates were significantly higher in the SS80 than in the control group, however, their growth rates in the D2 group were no different than in the control. Mean FE of the SS80 group (0.49), significantly exceeded those of the control (0.36) and D2 (0.28) groups. In contrast with the summer/fall experiment, no differences in growth rate were detected among the control, SS80 and D2 groups in the subsequent 84‐d spring experiment, where the juvenile walleye (97.45 g) were substantially larger, and their mean FE values were generally lower, with less distinction observed among the groups. Our findings indicate potential to increase growth and FE of juvenile walleye in advance of fall, by applying restrict‐feed schedules.     

Compensatory growth response of European sea bass (Dicentrarchus labrax L.) under cycled starvation and restricted feeding rate

The compensatory growth response of the European sea bass (Dicentrarchus labrax) that faced cycling starvation and restricted ration was assessed. Juveniles (10.5 g) were stocked into 15 tanks at a density of 25 fish per tank. Five different feeding regimes were tested on triplicate groups of fish: C_Satiation: control fed for 60 days without deprivation, C_Restricted: 25% restricted feeding, S‐R: 1 day starvation then 4 days C_Restricted feeding, R‐F: 1 day C_Restricted feeding then 4 days C_Satiation feeding, and, finally, S‐F: 1 day starvation then 4 days C_Satiation feeding. The specific growth rate of fish in the C_Satiation (2.5 ± 0.06% day^?1), S‐F (2.5 ± 0.11% day^?1) and R‐F (2.4 ± 0.18% day^?1) were significantly higher than that of C_Restricted (2.2 ± 0.05% day^?1) or S‐R (2.0 ± 0.01% day^?1). Fish in S‐F group were able to achieve catching up with the C_Satiation. There was no significant difference in feed conversion rates but R‐F and S‐F consumed approximately 34% more feed than C_Satiation following the first re‐feeding day. Although, the highest lipid content was observed in C_Satiation (14.4%), S‐R (33.3% dry matter) had the highest water content compared with the C_Satiation and C_Restricted (37.8% and 36.9% dry matter respectively). In conclusion, it may be concluded that sea bass has rapid response to cycling starvation/re‐feeding and that a 25% restricted feeding ratio is insufficient to invoke a compensatory growth response in sea bass.     

Dietary tryptophan requirement of fingerling Catla catla (Hamilton) based on growth,protein gain,RNA/DNA ratio,haematological parameters and carcass composition

A 12‐week feeding trial was conducted in eighteen 70 L indoor polyvinyl circular troughs provided with a water flow‐through system (1–1.5 L min^?1) at 28 ± 1 °C to evaluate the dietary tryptophan requirement of fingerling Catla catla (3.45 ± 0.24 cm; 0.60 ± 0.13 g). Six casein‐gelatin‐based amino acid test diets (330 g kg^?1 crude protein; 13.6 kJ g^?1 digestible energy) containing graded levels of L‐tryptophan (1.0, 1.4, 1.9, 2.3, 2.8, 3.4 g kg^?1 dry diet) were fed to triplicate groups of fish near to satiation at 08:00, 12:30 and 17:30 h. Absolute weight gain, feed conversion ratio, protein gain, RNA/DNA ratio, hepatosomatic index, viscerosomatic index, condition factor and haematological indices improved with the increasing levels of tryptophan from 1.0 to 2.3 g kg^?1 of dry diet. Significantly higher carcass protein was obtained at 2.3 g tryptophan per kilogram of the dry diet. Exponential analysis of absolute weight gain, feed conversion ratio, protein gain and RNA/DNA ratio against dietary tryptophan levels at 95% maximum and minimum responses displayed the tryptophan requirement at 2.5, 2.3, 2.5 and 2.1 g kg^?1 dry diet, respectively. Inclusion of dietary tryptophan in the range of 2.1–2.5 g kg^?1 dry diet, equivalent to 6.4–7.6 g kg^?1 dietary protein, is recommended in formulating tryptophan‐balanced feed for the culture of this fish species.