Dietary isoleucine requirement of fingerling Indian major carp, Labeo rohita (Hamilton)

An 8‐week feeding experiment was conducted to quantify the dietary isoleucine requirement of fingerling Indian major carp, Labeo rohita (3.50 ± 0.04 cm; 0.40 ± 0.02 g) using amino acid test diets (400 g kg⁻¹ crude protein; 17.90 kJ g⁻¹ gross energy) containing casein, gelatin and l ‐crystalline amino acids. Six dietary treatments supplemented with graded levels of isoleucine (7.5, 10.0, 12.5, 15.0, 17.5 and 20.0 g kg⁻¹), in gradations of 2.5 g kg⁻¹ diet, were fed to triplicate groups of fingerlings to apparent satiation divided over two feedings at 07:00 and 17:30 h. Performance of the fish was evaluated on the basis of live weight gain, feed conversion ratio (FCR), protein efficiency ratio (PER), specific growth rate (SGR) and protein productive value (PPV). Statistical analysis of live weight gain, FCR, PER, SGR and PPV reflected significant differences among treatments. Live weight gain and conversion efficiencies were best with isoleucine at 15.0 g kg⁻¹ of diet. Live weight gain, FCR, PER, SGR and PPV data were also analysed using second‐degree polynomial regression analysis to obtain more accurate isoleucine requirement estimate which was found to be at 15.9, 15.3, 15.2, 15.8 and 15.7 g kg⁻¹ of dry diet, corresponding to 39.8, 38.3, 38.0, 39.5 and 39.3 g kg⁻¹ of dietary protein respectively. Based on the quadratic regression analysis of the live weight gain, FCR, PER, SGR and PPV, the optimum level of isoleucine for fingerling L. rohita is in the range of 15.2–15.9 g kg⁻¹ of dry diet, corresponding to 38.0–39.8 g kg⁻¹ of dietary protein. Maximum body protein, minimum moisture and fat were noted at 15.0 g kg⁻¹ of dietary isoleucine while the body ash remained constant among all the treatment levels. No mortality was recorded during the duration of the experiment.     

Growth and metabolism of pacu (Piaractus mesopotamicus Holmberg 1887) juveniles fed diets containing different protein, lipid and carbohydrate levels

To verify the potential of lipids and carbohydrates to spare dietary protein and to understand the intermediary metabolism of interaction of these nutrients in pacu juveniles, an experiment was carried out to evaluate pacu physiological and performance parameters. The experimental design was completely randomized with 12 treatments in a 2 × 2 × 3 factorial arrangement, consisting of diets containing two digestible protein levels (200 and 230 g kg⁻¹ PD), two lipid levels (40 and 80 g kg⁻¹) and three carbohydrate levels (410, 460 and 500 g kg⁻¹). Fish‐fed 230 g kg⁻¹ digestable protein (DP) showed increased glycaemia, decreased hepatic glycogen, as well as a smaller intake index and better feed conversion ratio. The higher dietary lipid level (80 g kg⁻¹) reduced protein intake and serum protein concentration, increased liver and body fat content, but did not affect growth. At a lipid level of 80 g kg⁻¹, the increase in dietary carbohydrate levels promoted greater weight gain (WG), crude protein intake (CPI) and better feed conversion ratio (FCR). For fish fed diets containing 40 g kg⁻¹ lipid, the best energy‐productive values (EPV) were obtained at 460 g kg⁻¹ carbohydrate. Increased levels of the main nutrients in the diets reduced the levels of serum triglycerides, while the increase in energy concentration increased the hepatosomatic (HSI) and glycaemia index values. Pacu used lipids as effectively as carbohydrates in the maximization of protein usage, as long as dietary protein was at a level of 230 g kg⁻¹ DP. The physiological parameters indicated that the best balance between the DP, dietary lipid and carbohydrate levels within the ranged this trial was obtained at 230, 40 and 460 g kg⁻¹, respectively, without lower growth.     

Growth,feed utilization and body composition of Asian catfish (Pangasius hypophthalmus) fed at different dietary protein and lipid levels

This study examined the effect of dietary protein and lipid levels on growth, feed utilization and body composition of Asian catfish Pangasius hypophthalmus reared in cages. Eight test diets were formulated at four protein (340, 380, 420 and 460 g kg⁻¹ crude protein) and two lipid (50 and 90 g kg⁻¹ crude lipid) levels. Fish (initial weight 4.7 g fish⁻¹) were fed the test diets for 8 weeks. Final body weight, weight gain (WG), feed intake (FI), feed conversion ratio (FCR), contents of crude protein, lipid and energy in whole body were dependent on both dietary protein and lipid levels, while specific growth rate (SGR), hepatosomatic index and body moisture content were dependent on dietary lipid level. The WG and SGR increased with the increase in either dietary protein level (at the same lipid level) or lipid level (at the same protein level). The FI and FCR decreased with the increase in dietary protein level (at the same lipid level) or lipid level (at the same protein level). Protein sparing action occurred in case dietary lipid level increased. Fish fed the diet containing 453 g kg⁻¹ crude protein and 86 g kg⁻¹ lipid had the highest WG and SGR, but the lowest FI and FCR, among the diet treatments. There were no significant differences in the protein retention efficiency (PRE) and energy retention efficiency (ERE) among the diet treatments, although PRE and ERE were relatively high in fish fed the diet containing 453 g kg⁻¹ crude protein and 86 g kg⁻¹ lipid. At the end of the feeding trial, body protein content increased, while body lipid content decreased, with the increase in dietary protein content at the same lipid level. Our results suggest that dietary levels of 450 g kg⁻¹ crude protein and 90 g kg⁻¹ lipid are adequate to support fast growth of P. hypophthalmus reared in cages.     

Energy and nutrient utilization of Atlantic cod, Atlantic salmon and rainbow trout fed diets differing in energy content

The growth and feed utilization of Atlantic cod (Gadus morhua) (437 g), Atlantic salmon (Salmo salar) (485 g) and rainbow trout (Oncorhynchus mykiss) (413 g) fed a diet (170 g kg⁻¹ fat, 600 g kg⁻¹ crude protein; LE) similar to that used in commercial cod production or one that was top dressed with additional fat (280 g kg⁻¹ fat, 530 g kg⁻¹ crude protein; HE), were compared in an 11‐week trial. In the cod, relative feed intake was 41–58% and thermal growth coefficient 63% of that in the salmonids, but the feed efficiency ratio (FER) was 38% better (P ≤ 0.05). In contrast to the cod where there was no effect of diet on feed intake, growth or FER, both the salmon and trout fed the HE diet had greater feed intake than those fed the LE diet, but the effect of this was only positive for growth in the salmon. The cod retained more of the digested nitrogen (44.9 ± 2.7%) than the salmon (39.4 ± 0.8%), and both of these species retained more than the trout (33.6 ± 1.1%) (P ≤ 0.05). The retention of digested energy was significantly higher in the salmon (52.2 ± 0.9%) than in the trout (44.8 ± 1.1%), with the cod (44.9 ± 4.9%) not different from either of the other species. There were no differences between the species in the retention of absorbed phosphorus (65.9 ± 3.6%). There were very few dietary effects on nutrient utilization in this trial and, for the cod, this indicates that higher energy diets may be feasible for use in production.     

Growth,feed efficiency and body composition of juvenile cobia (Rachycentron canadum Linnaeus, 1766) fed increasing dietary levels of shrimp protein hydrolysate

A shrimp protein hydrolysate (SPH) containing 894.2 g kg⁻¹ crude protein (CP) and 54.3 g kg⁻¹ total lipids was tested as a partial replacement for fish meal (FM) in diets of juvenile cobia. The effects of increasing dietary levels of SPH on the survival, weight gain (WG), specific growth rate (SGR), feed conversion ratio (FCR), nitrogen retention efficiency (NRE) and daily feed intake (DFI) of cobia with initial body weight of 11.9 g were evaluated. Four isoproteic (from 431.1 to 439.7 g kg⁻¹) and isoenergetic (20 825–21 347 MJ kg⁻¹) diets were formulated to contain 0 (Control), 120, 240 or 360 g kg⁻¹ of dietary CP derived from SPH. Survival, WG, SGR, FCR, NRE and DFI ranged from 90 to 100%, 40.2–56.5 g, 4.7–6.1% day⁻¹, 1.04–1.54, 26.3–44.0% and 4.7–6.0% fish⁻¹ day⁻¹ respectively. Survival and DFI were not affected by the dietary treatments. On the other hand, fish fed the control diet and the one containing 120 g kg⁻¹ SPH had higher WG, SGR and FCR. Nitrogen retention efficiency was significantly higher for fish fed diets 0 and 120. It is concluded that up to 120 g kg⁻¹ of SPH in cobia diets can be used with no significant effects on feed utilization and fish performance.     

Growth,feed utilization,body composition and swimming performance of giant croaker,Nibea japonica Temminck and Schlegel,fed at different dietary protein and lipid levels

A 50‐day feeding trial was conducted to examine the effects of dietary protein and lipid levels on growth, feed utilization, body composition and swimming performance of giant croaker, Nibea japonica. Fish (initial body weight 44.6 g ind⁻¹) were fed ten test diets which were formulated at 5 crude protein levels (360, 400, 440, 480 and 520 g kg⁻¹) and 2 crude lipid levels (90 and 150 g kg⁻¹). In addition, a raw fish diet (fillet of small yellow croaker) served as the reference. The weight gain (WG) increased, whereas the feed intake (FI) and feed conversion ratio (FCR) decreased, with increasing dietary protein level from 360 to 520 g kg⁻¹. At the same dietary protein level, no significant difference was found in the WG between fish fed the diets containing 90 or 150 g kg⁻¹ crude lipid. Fish fed the diet containing 480 g kg⁻¹ crude protein and 90 g kg⁻¹ crude lipid exhibited higher WG, nitrogen retention efficiency (NRE) and energy retention efficiency (ERE) but lower nitrogen wastes output (TNW). At the end of the feeding trial, the hepatosomatic index (HSI) and viscerosomatic index (VSI) decreased, whereas the body protein content increased, with increase in dietary protein level. The body lipid content was higher in fish fed at the 150 g kg⁻¹ lipid level than in fish fed at the 90 g kg⁻¹ lipid level. No significant difference was found in the maximum sustained swimming speed (MSS) between fish fed at different dietary protein and lipid levels. The WG, NRE, ERE and condition factor (CF) were higher, whereas the FI, FCR, HSI, VSI and TNW were lower, in fish fed the raw fish diet than in fish fed the diet containing 480 g kg⁻¹ crude protein and 90 g kg⁻¹ crude lipid. No significant difference was detected in the MSS between fish fed the raw fish diet and diet containing 480 g kg⁻¹ crude protein and 90 g kg⁻¹ crude lipid. The results of this study suggest that the suitable dietary crude protein and crude lipid levels are 480 g kg⁻¹ and 90 g kg⁻¹ for giant croaker reared in net pens.     

The effect of temperature and dietary fat level on tissue lipid composition in Atlantic salmon (Salmo salar) fed wax ester‐rich oil from Calanus finmarchicus

Copepod oil (CO) from the marine zooplankton, Calanus finmarchicus, is a potential alternative to fish oils (FOs) for inclusion in aquafeeds. The oil is composed mainly of wax esters (WE) containing high levels of saturated fatty acids (SFAs) and monounsaturated fatty alcohols that are poorly digested by fish at low temperatures. Consequently, tissue lipid compositions may be adversely affected in salmon‐fed CO at low temperatures. This study examined the lipid and FA compositions of muscle and liver of Atlantic salmon reared at two temperatures (3 and 12 °C) and fed diets containing either FO or CO, supplying 50% of dietary lipid as WE, at two fat levels (～330 g kg^?1, high; ～180 g kg^?1, low). Fish were acclimatized to rearing temperature for 1 month and then fed one of four diets: high‐fat fish oil (HFFO), high‐fat Calanus oil (HFCO), low‐fat fish oil (LFFO) and low‐fat Calanus oil (LFCO). The fish were grown to produce an approximate doubling of initial weight at harvest (220 days at 3 °C and 67 days at 12 °C), and lipid content, lipid class composition and FA composition of liver and muscle were determined. The differences in tissue lipid composition between dietary groups were relatively small. The majority of FA in triacylglycerols (TAG) in both tissues were monounsaturated, and their levels were generally higher at 3 °C than 12 °C. Polyunsaturated fatty acids (PUFA), particularly (n‐3) PUFA, predominated in the polar lipids, and their level was not significantly affected by temperature. The PUFA content of TAG was highest (～26%) in the muscle of fish fed the HFCO diet at both temperatures. Tissue levels of SFAs were lower in fish‐fed diets containing HFCO than those fed HFFO, LFFO or LFCO, particularly at 3 °C. The results are consistent with Atlantic salmon being able to incorporate both the FA and fatty alcohol components of WE into tissue lipids but, overall, the effects of environmental temperature on tissue lipids were more pronounced in fish fed the CO diets than FO diets.     

Protein‐sparing capability of dietary lipid in herbivorous and omnivorous freshwater finfish: a comparative case study on grass carp (Ctenopharyngodon idella) and tilapia (Oreochromis niloticus × O. aureus)

Two, 8‐week feeding trials were conducted to compare protein‐sparing capability of dietary lipid in herbivorous grass carp (Ctenopharyngodon idella) and omnivorous tilapia (Oreochomis niloticus × O. aureus). Utilizing a 2 × 3 factorial design, experimental diets containing two levels of crude protein (380 and 250 g kg⁻¹) and three levels of lipid (0, 40 and 100 g kg⁻¹) were formulated for use in both feeding trials. Growth performances showed better response of both fish fed 380 g kg⁻¹ protein diet than those fed 250 g kg⁻¹ protein diet. Despite the dietary protein level, weight gain (WG), specific growth ratio (SGR), feed conversion ratio (FCR) and protein efficiency ratio were much higher (P < 0.05) for grass carp fed 40 g kg⁻¹ lipid diet than those fed 100 g kg⁻¹ lipid diet; however, there were no significant differences in tilapia fed the two diets. The feed intake of grass carp fed lipid‐free diet was the lowest, but it tended to decrease with increase in dietary lipids in tilapia. Lipid retention (LR) was negatively correlated with dietary lipid concentration of both fish. Viscerosomatic index (VSI), hepatosomatic index (HSI), intraperitoneal fat ratio (IPF) and whole‐body and liver lipid content positively correlated with dietary lipid concentration of both fish. Plasma parameters and liver enzymes activities were also positively correlated with dietary lipid concentration of both fish. Liver lipid contents were higher and enzymes activities were lower in grass carp when compared with tilapia. These data suggested that there was no evidence of a protein‐sparing effect of dietary lipids in grass carp. Tilapia has relatively higher capacity to endure high dietary lipid level compared to grass carp.     

Optimum dietary protein and lipid levels for growth of juvenile sea cucumber Apostichopus japonicus

A feeding trial of three protein (200, 300 and 400 g kg⁻¹) and two lipid levels (20 and 100 g kg⁻¹) was conducted to determine the proper dietary protein and lipid levels for growth of juvenile sea cucumber Apostichopus japonicus. Dietary protein and lipid levels were adjusted by adding with different levels of soybean meal, squid liver oil and soybean oil, respectively. Three replicate groups of sea cucumbers (average weight of 1.3 g) were fed the experimental diets for 12 weeks. At the end of the feeding trial, survival was not affected by dietary protein and lipid levels (P > 0.05). Weight gain (WG) and specific growth rate (SGR) of sea cucumbers were significantly affected by dietary protein (P < 0.006) and lipid levels (P < 0.001). The highest WG and SGR were observed in sea cucumbers fed the 200 and 400 g kg⁻¹ protein diet with 20 g kg⁻¹ lipid (P < 0.05). WG and SGR of sea cucumbers fed the diet containing 20 g kg⁻¹ lipid were higher than those of sea cucumbers fed the 100 g kg⁻¹ lipid diets (P < 0.05) at each dietary protein level. Apparent digestibility coefficients of dry matter, crude protein, carbohydrate and gross energy of sea cucumbers fed the 20 g kg⁻¹ lipid diets were significantly higher than those of the 100 g kg⁻¹ lipid diets at 200 and 400 g kg⁻¹ protein (P < 0.05). Moisture, crude protein, crude lipid and ash contents were not significantly different among the groups. The results of this study indicate that the diet containing 200 g kg⁻¹ protein (170 g kg⁻¹ digestible protein) with 20 g kg⁻¹ lipid (13 g kg⁻¹ digestible lipid) may be sufficient for optimum growth of juvenile sea cucumber.     

Dietary protein/energy ratios for Atlantic salmon in relation to fish size: growth, feed utilization and slaughter quality

Four extruded diets differing in protein/fat concentrations, 378/389 g kg^?1, 425/346 g kg^?1, 480/308 g kg^?1 and 524/256 g kg^?1 were tested in a digestibility trial and a growth study. Apparent digestibility of protein and fat were not significantly different among the diets when tested in 1-kg Atlantic salmon, Salmo salar L., in sea water. The diets represented a range of digestible protein to digestible energy ratios (DP/DE ratios) of 14.1, 16.4, 18.8 and 21.9 g MJ^?1. The 138-day growth study was performed with triplicate groups of Atlantic salmon of 1.0 and 2.5 kg initial weight. Irrespective of size; growth, feed conversion ratio (FCR), nitrogen and energy retention were poorer in fish fed the diet with DP/DE ratio of 14.1 g MJ^?1 compared with the fish fed the other diets. A DP/DE ratio of 16.4 g MJ^?1 was sufficient to produce maximum growth for the large fish, while the DP/DE ratio of 18.8 g MJ^?1 produced the highest growth in the small fish. In the large fish, the lowest FCR was obtained on a DP/DE ratio of 16.4 g MJ^?1, while there was no clear difference in FCR within the small fish when diets of DP/DE ratios of 16.4–21.9 g MJ^?1 were fed. The carcass-to-body ratio in the small fish decreased with decreasing DP/DE ratios. The fish fed the diet of 21.9 g MJ^?1 had significantly lower fat and dry matter and higher protein content than fish of similar size fed the other diets. Increased dietary lipid content seemed to improve astaxanthin deposition in the small fish, while the large fish showed no significant differences in astaxanthin deposition due to dietary treatment. This study indicates that a DP/DE ratio of 14.1 g MJ^?1 in high-energy diets for Atlantic salmon in sea water is below the optimal DP/DE ratio for growth and feed utilization, and that the optimal DP/DE ratio decreases with increasing fish weight. DP/DE ratios around 19 g MJ^?1 for fish weighing 1 to 2.5 kg, and 16–17 g MJ^?1 for fish weighing 2.5 to 5 kg, are suggested to be optimal.