Dietary threonine requirement of juvenile large yellow croaker,Larmichthys crocea

A feeding trial was conducted to determine the dietary threonine requirement of juvenile large yellow croaker (Larmichthys crocea). Six diets were formulated containing 45% crude protein with six graded levels of threonine (0.71–2.46% in about 0.35% increment). Each diet was randomly assigned to triplicate groups of 60 juvenile fish (initial body weight 6.00 ± 0.10 g). Fish were fed twice daily (05:00 and 16:30) to apparent satiation for 8 weeks. The result indicated that significant difference was observed in the weight gain among all treatments. Specific growth rate (SGR), feed efficiency (FE), protein efficiency ratio (PER) and nitrogen retention (NR) increased with increasing levels of threonine up to 1.75% diet (P < 0.05), and thereafter, declined. No significant differences in body dry matter, crude protein, crude lipid or ash content were found among dietary treatments. Theronine contents of fish muscle were significantly affected by dietary threonine levels (P < 0.05). Fish fed the diet with 0.71% threonine showed the lowest threonine content (2.94%) in fish muscle, while fish fed the diet with 1.75% threonine had the highest value (3.16%). Other essential amino acid contents of muscle were not significantly different among the dietary treatments. On the basis of SGR, FE or NR, the optimum dietary threonine requirements of juvenile L. crocea were estimated to be 1.86% of diet (4.13% of dietary protein), 1.90% of diet (4.22% of dietary protein) and 2.06% of diet (4.58% of dietary protein), respectively, using second‐order polynomial regression analysis.     

The effects of dietary protein levels with amino acid supplementation on the growth performance,haematological profile and histology of meagre (Argyrosomus regius) in two different size classes

A 12‐week feeding trial was conducted to estimate the effects of supplemented amino acids (lysine and methionine) with different dietary protein levels on growth, haematology and liver histology in meagre (Argyrosomus regius) at two different sizes: fingerling (15.2 g) and juvenile (44.4 g). Six practical diets were prepared, and three of these practical diets were formulated with 40 (P40), 44 (P44) and 48% (P48) crude protein without supplementation of amino acids. Other three diets having same protein levels were supplemented with lysine and methionine (P40AA, P44AA and P48AA) to bring these amino acids level up to that estimated to be at the least in the 48% protein diet. Final mean weight (FMW) and specific growth rate (SGR) of P48AA in fingerlings were higher than that of 40AA. According to FMW and SGR of juveniles, there was interaction found between dietary protein levels and the supplementation of amino acids. The FMW and SGR of meagre fed P44AA were higher than that of fish fed the other diets, except fish fed the P48. Economic profit index, packed cell volume and haemoglobin for juvenile meagre were significantly improved with the dietary protein level and amino acid supplementation. The liver tissues of the P48 group in both sizes displayed better structure compared with the other groups. In conclusion, dietary crude protein content of practical diets for juvenile meagre could be reduced from 48% to 44% by adding essential amino acids with an enhancement in growth, health and economic profit.     

Effect of Dietary Lipid Level and Protein Energy Ratio on Growth and Body Composition of Largemouth Bass Micropterus salmoides

A feeding trial was conducted in aquaria with juvenile largemouth bass Micropterus salmoides to examine the effects of increasing dietary lipid levels on growth and body composition. Feed‐trained largemouth bass fingerlings were graded to a similar size (16.3 ± 2.4 g) and randomly stocked into 15 113.6‐L glass aquaria at 25 fish/aquarium. Fingerlings were fed twice daily to apparent satiation with one of five isonitrogenous extruded experimental diets based on practical ingredients. Diets contained approximately 40% crude protein and either 0, 5, 10, 15, or 20% added lipid. Due to background lipids in the ingredients, this equated to total lipid levels of 7, 10, 16, 20, and 23%, respectively. These diets had protein to energy ratios of 137, 120, 106, 95, and 86 mg/kcal, respectively. There were three replicate aquaria per dietary treatment. After 12 wk, there were no statistically significant differences (P > 0.05) in average weight (g), specific growth rate (% body weight/d), survival (%), or protein efficiency ratio (PER, %) among fish fed the five diets, which averaged 79.3 ± 5.6, 1.9 ± 0.1, 99.5 ± 1.5, and 2.11 ± 0.19, respectively. Juvenile largemouth bass fed diets containing 15 and 20% added lipid had significantly lower (P± 0.05) feed conversion ratios (FCR) (1.1 ± 0.0 and 1.1 ± 0. 1, respectively) than fish fed diets containing 0, 5, and 10% added lipid (1.4 ± 0.1, 1.3 ± 0. 1, and 1.3 ± 0.2, respectively). Proximate analysis of whole body samples indicated a significantly higher (P ± 0.05) lipid content in fish fed 15 and 20% added lipid compared to fish fed lower lipid levels. While FCR was lowest in fish fed the 15 and 20% added lipid diets, increased whole body lipid deposition may indicate that these levels are above optimal levels for juvenile largemouth bass. It appears that 7–16% total dietary lipid (P/E:137–106 mg/kcal) is sufficient to support efficient growth without impacting body composition in juvenile largemouth bass when fed a diet containing 40% crude protein.     

Optimum Dietary Protein Level and Protein‐to‐energy Ratio for Growth of Juvenile Parrot Fish,Oplegnathus fasciatus

An 8‐wk feeding trial was conducted to estimate the optimum dietary protein level and protein‐to‐energy (P/E) ratio in juvenile parrot fish, Oplegnathus fasciatus. Eight experimental diets were formulated with two energy levels and four protein levels for each energy level. Diets containing crude protein (CP) at 35, 40, 45, and 50% had either 12.5 or 14.6 kJ/g of energy. Fish averaging 7.1 ± 0.06 g (mean ± SD) were fed one of the experimental diets for 8 wk. At the end of the feeding trial, weight gain (WG) of fish fed 45 and 50% CP in the 12.5 kJ/g diet was significantly higher than fish fed the 35% CP diet (P < 0.05). WG of the fish fed 45 and 50% CP in the 14.6 kJ/g diet was significantly higher than fish fed the 35 and 40% CP diets (P < 0.05). Fish fed the 14.6 kJ/g diet had a higher WG compared with fish fed the 12.5 kJ/g diet at all CP levels. Feed efficiency (FE) and specific growth rate (SGR) showed a similar trend to the WG. WG, FE, and SGR improved with increasing dietary protein levels up to 45% and remained constant at 50% CP for both energy levels. However, protein efficiency ratio was negatively related to dietary protein levels. The results suggested that the optimum level of protein and the optimum P/E ratio for juvenile parrot fish should be 45% and 31.1 mg protein/kJ, respectively, in a diet containing 14.6 kJ/g energy.     

Evaluation of dietary protein and lipid requirements of two-banded seabream (Diplodus vulgaris) cultured in a recirculating aquaculture system

The objective of this study is to investigate the effects of dietary protein and lipid levels on the growth performance and bioeconomic benefits of two-banded seabream (Diplodus vulgaris) juveniles, a candidate species for aquaculture sector. Eight experimental diets were formulated with four protein (50, 45, 40 and 35 %) levels for each of the two lipid levels (15 and 10 %). Triplicate groups of juvenile fish with an average initial body weight of ~3.64 g were reared in a recirculating aquaculture system and hand fed twice a day until satiation for a period of 60 days. In the experiment, no difference in survival rate was found between the different groups. Relative growth rate (RGR), specific growth rate (SGR), feed conversion ratio (FCR) and daily feed intake were not significantly affected by increasing protein and/or lipid treatments in this present study. However, the RGR, SGR and FCR values showed slightly better efficiency in the experimental group (35/15) fed with lower protein content (35 %) and higher lipid level (15 %) compared with those fed other diets. According to bioeconomic analyses results, the diet with the 35 % protein and 15 % lipid generated the best profit. The results suggest that two-banded seabream can be accepted as a promising alternative species for the aquaculture industry and optimum growth of two-banded seabream fingerlings can be obtained when they are fed a diet containing 35 % crude protein and 15 % crude lipid.     

Replacement of fishmeal in cobia (<Emphasis Type="Italic">Rachycentron canadum</Emphasis>) diets using poultry by-product meal

An 8-week feeding trial was conducted to evaluate the use of local poultry by-product meal (PBM) in replacement of imported fishmeal in the diets of cobia, Rachycentron canadum. Six isolipidic (12%) and isoproteic (45%) experimental diets were formulated using PBM to replace fishmeal at 20, 40, 60, 80 and 100% dietary protein. Eleven juvenile cobia (initial mean weight of 30.7 ± 0.78 g) were randomly stocked in 300-L circular fibreglass tanks and hand-fed based on the total biomass of each tank, twice a day at 0900 h and 1500 h. The fish were group weighed at 2-week intervals to monitor their growth performance in order to adjust the feeding ratio. At the end of the feeding trial, weight gains (WGs) ranging from 221 to 322% were obtained. The specific growth rate (SGR), WG and protein efficiency ratio (PER) for fish fed with PBM-based diets were not significantly different (P > 0.05) when compared to fish fed the control diet. The best SGR was recorded for fish fed with 60PBM diet, which was significantly higher (P < 0.05) than those fed the control diet with values at 2.40 ± 0.01 and 1.97 ± 0.26%/day, respectively. The FCR of 1.83 ± 0.05 for fish fed the 60PBM diet was not significantly different (P > 0.05) when compared to those fed the control diet. The PBM source and dietary level did not significantly (P > 0.05) affect the hepatosomatic index of the fish. The results from this study suggested that PBM could replace 100% dietary fishmeal without adversely affecting the growth performance, but an optimal replacement level at approximately 60% was recommended for better growth performance and efficient feed utilization.     

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.     

Effects of dietary protein levels on growth,feed utilization,protein retention efficiency and body composition of young <Emphasis Type="Italic">Heteropneustes fossilis</Emphasis> (Bloch)

An 8-week growth trial was conducted to assess the effect of dietary protein on growth, feed utilization, protein retention efficiency, and body composition of young Heteropneustes fossilis (10.02 ± 0.09 g; 9.93 ± 0.07 cm). Isocaloric (4.15 kcal g⁻¹, GE) diets with varying levels of protein (25, 30, 35, 40, 45, and 50% of the diet) were fed near to satiation to triplicate groups of fish. Optimum dietary protein was determined by analyzing live weight gain (LWG%), feed conversion ratio (FCR), protein efficiency ratio (PER), specific growth rate (SGR%), and protein retention efficiency (PRE%) data. Maximum LWG% (167), best FCR (1.42), PER (1.75), SGR (1.76), and PRE (31.7%) were evident in fish fed 40% protein diet (Diet 4). Body protein data also supported the above level. However, second-degree polynomial regression analysis of the above data indicated that inclusion of dietary protein in the range of 40–43% is optimum for the growth of young H. fossilis.     

Effects of phospholipid addition to diets with different inclusion levels of fish oil on growth and fatty acid body composition of juvenile swimming crab Portunus trituberculatus

Six experimental diets were designed with two phospholipid (PL; 0% and 1.5%) and three fish oil levels (0%, 1% and 3%) to evaluate the effects of dietary fish oil and PL levels on growth, survival and fatty acid composition of juvenile swimming crab, Portunus trituberculatus. Diets were iso‐energetic and iso‐nitrogenous and each diet was fed to triplicate groups (initially weight, 24.88 ± 0.04 g per crab) for 59 days. Weight gain (WG) and specific growth rate (SGR) increased with dietary PL addition to 0% fish oil‐supplemented diets (P < 0.05). On the other hand, WG and SGR decreased with dietary PL addition to 3% fish oil diets (P < 0.05). Crabs fed PL supplemented diets had higher haemolymph low‐density lipoprotein cholesterol concentrations and muscle crude lipid levels (P < 0.05) than crabs fed a none PL supplemented diet. The percentage of highly unsaturated fatty acids (HUFA; % total FA) in both polar and neutral lipids fractions of muscle tissue only increased in case of PL addition to 0% and 1% fish oil‐supplemented diets (P < 0.05). HUFA levels in the neutral lipids fraction of the hepatopancreas increased by dietary PL addition at each dietary fish oil level (P < 0.05). In this study, both dietary fish oil and PL addition contributed to a high n‐3/n‐6 ratio in muscle and hepatopancreas of P. trituberculatus. In conclusion, PL addition is only meaningful with fish oil‐deficient diets, in which case it enhanced lipid transport and HUFA absorption efficiency, hence improving the nutritional value of the diet.     

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.     

Evaluation of dietary natural mineral materials as an antibiotic replacer on growth performance,non‐specific immune responses and disease resistance in rainbow trout,Oncorhynchus mykiss

We evaluated the effects of some dietary natural mineral materials as an antibiotic replacer based on growth performance, non‐specific immune responses and disease resistance in juvenile and subadult rainbow trout, Oncorhynchus mykiss. First experiment, juvenile rainbow trout averaging 2.7 ± 0.02 g (mean ± SD) were fed one of the six experimental diets; a basal commercial diet as a control (CON), CON with oxytetracycline (OTC), with yellow loess (YL), with Macsumsuk^® (MS), with Song‐Gang^® stone (SG) and with barley stone (BS) at 0.4% of each diet. At the end of 8‐week feeding trial, weight gain (WG), specific growth rate (SGR), feed efficiency (FE) and protein efficiency ratio (PER) of fish fed YL diet were significantly higher than those of fish fed CON diet. Non‐specific immune responses such as superoxide dismutase (SOD), myeloperoxidase (MPO), lysozyme (LYS) activity and oxidative radical production of fish fed YL diet were higher than those of fish fed CON diet. At the end of 15 days of challenge test with Aeromonas salmonicida, average cumulative survival rate of fish fed YL diet was significantly higher than that of fish fed BS and CON diets. However, there were no significant differences among fish fed YL, SG and OTC diets. Second experiment, subadult rainbow trout averaging 261.5 ± 3.5 g (mean ± SD) were fed one of the four experimental diets for 22 weeks: CON, and CON with OTC, YL or SG at 0.4% of each diet. At the end of feeding, growth performance of fish fed SG and YL diets was significantly higher than that of fish fed CON diet. Non‐specific immune responses in terms of SOD, MPO, LYS and NBT of fish fed SG and YL diets were significantly higher than those of fish fed CON diet. However, there were no significant differences among the fish fed YL, SG and OTC diets. The results indicate that dietary yellow loess or Song‐gang^® stone at 0.4% of diet could replace oxytetracycline in juvenile and subadult rainbow trout.     

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.     

Effect of dietary lipid on growth,body composition,serum biochemistry and hepatic metabolite alteration in Chinese rice field eel (Monopterus albus) fingerlings

Five isonitrogenous and isocaloric diets containing dietary lipid concentrations from 71.90 to 142.70 g/kg were formulated and fed to Chinese rice field eel Monopterus albus fingerlings (5.00 ± 0.50 g). The highest values of weight gain, specific growth rate (SGR), together with the lowest feed conversion ratio (FCR) were found in fish fed with 89.10 g/kg lipid diet. Fish fed with 71.90 g/kg diet (F1) had higher hepatosomatic index, viscerosomatic index and whole‐body crude lipid than fish in the other four treatments (p < .05). Plasma concentration of triacylglycerol and the activity of alanine aminotransferase were also higher in fish fed with F1 diet. Whole‐body fatty acid profile varied exclusively, but with a stable value of n?3/n?6 ratio. Gas chromatography–mass spectrometry‐based metabolomics identified eighteen differential metabolites (including idose, alanine, glutamic acid, serine and hypotaurine) in liver affected by dietary lipid content using PLS‐DA analysis. The subsequent pathway enrichment revealed ten affected pathways, with the top three pathways being glycine, serine and threonine metabolism; starch and sucrose metabolism; and D‐glutamine and D‐glutamate metabolism. The broken‐line model of SGR suggested that a dietary lipid concentration of 83.50 g/kg was appropriate for M. albus fingerlings.     

Dietary lysine requirement of juvenile dusky kob,Argyrosomus japonicus

To determine dietary lysine requirement of dusky kob, Argyrosomus japonicus, six isonitrogenous and isoenergetic diets (431 g/kg crude protein, 141 g/kg lipid and 20 kJ/kg) were formulated with graded levels of crystalline L‐lysine (18–42 g/kg of the dry diet). The protein source in the basal diet comprised fishmeal and soya, where a combination of L‐aspartic and L‐glutamic acids was maintained at a ratio of 1:1, and all diets were supplemented with a mixture of crystalline essential amino acids to simulate the amino acid profile in dusky kob. Dietary treatments were randomly assigned to triplicate groups of 12 fish (4.5 ± 0.2 g, mean weight; 66.5 ± 1.1 mm, total length ± SD), which were fed to apparent satiation three times daily for 12 weeks. The fish fed dietary L‐lysine at 21, 29 and 33 g/kg dry diet showed the highest specific growth rates (SGR) and the lowest feed conversion ratio. For most amino acids, retention in the body of the fish increased with an increase in dietary lysine from 18 to 21 g/kg, and it reached a maximum somewhere between 21 and 33 g/kg, where after amino acid retention decreased with increasing dietary lysine. Based on SGR and using segmented broken‐line analysis, the dietary L‐lysine requirement of juvenile dusky kob was estimated at 31.7 ± 1.6 g/kg dry diet corresponding to 73.5 g lysine per kg protein.     

Dietary protein requirement of juvenile kelp grouper (Epinephelus moara)

Dietary protein requirement of juvenile kelp grouper Epinephelus moara was investigated through a feeding trial. Experimental diets with graded crude protein (CP) levels (33.01%, 38.54%, 45.21%, 50.71%, 56.10% and 63.09% of dry matter respectively) were formulated. Six triplicate groups of fish (20 individuals per replicate with initial mean weight 6.00 g) were fed with each diet for 8 weeks. Best growth performance of fish was detected in 56.10% CP diet. The specific growth rate (SGR) significantly elevated with increasing dietary CP level to 50.71%, but there was no significant difference thereafter (p < .05). The feed conversion ratio (FCR) decreased significantly with dietary CP levels from 33.01% to 56.10% (p < .05). Glucose (GLU) and total protein (TP) concentrations in plasma had an increasing trend with dietary protein increasing. In the 33.01% CP group, plasma triglyceride (TG) content was significantly higher (1.67 mmol/L) than that in other dietary treatments (0.65–1.14 mmol/L). The lowest alanine transaminase (ALT) activity was observed in the 56.10% CP group (163.16 U/L). Crude lipid content in the muscle and liver was significantly elevated with increasing dietary protein levels (p < .05). The glycogen content in the liver decreased significantly as CP levels increased (p < .05). The fish fed diet with higher CP level (56.10% and 63.09%) had significantly higher energy retention (ER) and lipid retention (LR) than other treatments. Based on the broken‐line regression analysis of SGR and FCR, the optimal dietary protein requirement for juvenile kelp grouper is 54.61%–56.22%.     

Dietary arginine requirement of juvenile cobia ( Rachycentron canadum)

A 9‐week feeding trial was conducted to estimate the dietary requirement of arginine in juvenile cobia in indoor flow‐through and aerated aquaria. Six isonitrogenous and isoenergetic practical diets were formulated to contain graded levels of arginine ranging from 1.76% to 3.75% (dry weight) at about 0.4% increments replaced by equal proportions of glycine. Survival was not significantly different among dietary treatments. Specific growth rate (SGR) and feed efficiency ratio (FER) increased with increasing dietary arginine up to the 2.96% diet (P < 0.05), and thereafter declined. The whole body crude protein content was significantly affected by dietary arginine (P < 0.05), while moisture, crude lipid and ash showed no significant differences among dietary treatments. The essential amino acid contents of muscle were not significantly affected by dietary arginine. The serum nitric oxide synthase activities in fish fed diets with arginine from 2.18% to 3.75% were significantly higher than activities in fish fed the diet with 1.76% arginine (P < 0.05). On the basis of SGR and FER, the optimal dietary arginine requirements of juvenile cobia were estimated to be 2.85% of the diet (6.20% of dietary protein) and 2.82% of the diet (6.13% of dietary protein), respectively, using second‐order polynomial regression analysis.     

Influence of Ulva meal on growth, feed utilization, and body composition of juvenile Nile tilapia (Oreochromis niloticus) at two levels of dietary lipid

A nutrition trial was conducted to investigate the effects of dietary lipid levels and supplemental Ulva meal on growth performance, feed efficiency, nutrient utilization, and body composition of juvenile Nile tilapia, Oreochromis niloticus. Four isonitrogenous (CP 40%) diets containing 0% and 5% Ulva meal were formulated to contain 10% (low-lipid; LL) and 20% (high-lipid; HL) crude lipid. Triplicate groups of fish (~10 g) were fed to apparent satiation three times daily for 16 weeks. Fish fed 5% Ulva meal showed an increased growth performance (P < 0.05) compared with fish fed non-Ulva supplemented diets, irrespective of dietary lipid level. In particular, the incorporation of Ulva meal improved specific growth rate (SGR), feed conversion ratio (FCR), and protein efficiency ratio (PER). Feeding fish 5% Ulva meal diets resulted in significantly lower carcass lipid content. The results indicate that 5% inclusion of Ulva meal at both dietary lipid levels improves growth performance, feed efficiency, nutrient utilization, and body composition of Nile tilapia.     

Effect of increased dietary protein level in meagre (Argyrosomus regius) juvenile growth and muscle cellularity

In this study, two different dietary protein levels were tested (500 and 600 g/kg) in meagre juveniles of approximately 2 g, to determine whether a higher body protein diet would favour muscle growth. Results showed that meagre survival and growth were not affected by different levels of dietary protein. However, a higher content of protein was observed in the body composition of meagre fed the P60 diet (656 g/kg versus 624 g/kg). When fish were 82 days after hatched (DAH), protein retention efficiency was significantly higher in fish that were fed the P50 diet (37.1% versus 32.5%). Muscle cellularity changed considerably from the beginning to the end of the trial. The contribution of fibre hyperplasia to muscle growth was reduced although still accounted for 30% in 96 DAH meagre. Several differences were found in the frequency of fibres with areas between 1,000 μm² and 2,200 μm² between younger and older meagre, but no effect was found associated with dietary protein. This study suggests that neither growth nor muscle cellularity of fast‐growing juvenile meagre is positively affected by an increased dietary protein levels.     

饲料中添加生物素对草鱼幼鱼生长、体成分和血清生化指标的影响

在纯化饲料中分别添加生物素0、0.05、0.10、0.20、0.40、0.80、1.60 mg/kg投喂初始质量为(5.92±0.25)g的草鱼(Ctenopharyngodon idellus)幼鱼8周,研究了不同生物素添加量对草鱼幼鱼生长性能、饲料系数、机体营养成分、血清生化指标的影响。试验结果显示:与对照组相比,添加生物素提高了草鱼幼鱼的增重率、特定生长率,降低了饲料系数。添加量为0.40 mg/kg时草鱼幼鱼的特定生长率和增重率最大,饲料系数最低,并与对照组存在显著差异(P<0.05);添加不同水平生物素对草鱼幼鱼全鱼水分、粗蛋白、粗脂肪含量无显著影响,但添加量为0.40 mg/kg时粗蛋白含量最大。0.10 mg/kg组和0.20 mg/kg组的全鱼灰分含量显著高于对照组(P<0.05);添加生物素对血清总蛋白(TP)、血糖(GLU)和总胆固醇(TC)无显著影响,但显著提高了血清甘油三酯(TG)含量,各添加组TG含量均显著高于对照组(P<0.05),1.60 mg/kg添加组的高密度脂蛋白胆固醇(HDL-C)和低密度脂蛋白胆固醇(LDL-C)含量显著高于对照组(P<0.05)。综合本试验结果,草鱼幼鱼饲料中生物素适宜添加量为0.40 mg/kg。     

Influence of lipid level and supplemental lecithin in diet on growth,feed utilization and body composition of juvenile flounder (Paralichthys olivaceus) in suboptimal water temperatures

This study was conducted to investigate the influence of dietary lipid level and supplemental soy lecithin on growth, feed utilization and body composition of juvenile flounder reared at two suboptimal water temperatures, 12 and 17 °C. Three isonitrogenous (CP 50%) diets containing 1% squid liver oil (S7), 7% squid liver oil (S14), and a mixture of 2% soy lecithin and 5% squid liver oil (SL14) were formulated to obtain 7% and 14% of crude lipid. Triplicate groups of fish (6.3 ± 0.2 g) were fed to apparent satiation twice a day for 60 days. Weight gain, daily feed intake, feed efficiency and protein efficiency ratio were significantly higher for fish reared at 17 °C than at 12 °C. Daily feed intake was significantly decreased with the increase of dietary lipid level at the same water temperature, but weight gain was not affected by dietary lipid composition. At 12 °C, feed efficiency and protein efficiency ratio were significantly higher for fish fed the S14 and SL14 diets than those of fish fed the S7 diet, while at 17 °C feed efficiency and protein efficiency ratio of fish fed the S14 diet, which were not significantly different from those of fish fed the SL14 diet, were significantly higher than those of fish fed the S7 diet. There were no significant effects of dietary lipid composition or temperature range on the whole body contents of moisture, crude protein, lipid or ash. Dietary lipid composition and temperature affected the fatty acid content of the polar lipid from the liver; and the n-3HUFA contents such as 20:5n-3 and 20:6n-3 were higher at 12 °C than at 17 °C. The results of this study indicate that an increase of dietary lipid level from 7% to 14% has beneficial effects on feed utilization of flounder when reared in suboptimal water temperatures. The increase of water temperature from 12 to 17 °C improved growth and feed utilization, but 2% soy lecithin had no substantial effect on growth and feed efficiency of juvenile flounder.