Effects of dietary macronutrient level and feeding frequency on growth and body composition of juvenile rockfish (Sebastes schlegeli)

An 8-week feeding experiment was conducted to investigate the effects of different dietary macronutrient level and feeding frequency on the growth, feed utilization, and body composition of juvenile rockfish. Triplicate groups of fish (body weight of 4.1 g) were fed the experimental diets containing either high levels of carbohydrate (HC, 35%), lipid (HL, 13%), or protein (HP, 55%) at different feeding frequencies (twice daily, once daily, and once every 2 days). Weight gain was affected by feeding frequency but not by dietary composition. Weight gain of fish fed the diets once every 2 days was significantly (P < 0.05) lower than that of other groups. Daily feed intake and energy intake were affected by both dietary composition and feeding frequency. Daily feed intake of fish fed the HC diet was significantly (P < 0.05) higher than that of fish fed the HL and HP diets at the same feeding frequency. Feed efficiency and protein efficiency ratio were affected by both dietary composition and feeding frequency and decreased with increasing feeding frequency in the same dietary composition. Feed efficiency and protein efficiency ratio of fish fed the HC diet were significantly (P < 0.05) lower than those of fish fed the HL diet at the same feeding frequency. Whole-body lipid content of fish fed the HL diet was significantly (P < 0.05) higher than that of fish fed the HC and HP diets at the same feeding frequency. These results indicate that an increase of dietary lipid level compared with dietary carbohydrate level may have the advantage of a protein-sparing effect at same feeding frequency, and a once-daily feeding regime is more effective than twice daily or one feeding every 2 days to improve growth performance of juvenile rockfish grown from 4 to 21 g.     

Haematological and biochemical profile of harvest-size carp during harvest and post-harvest storage

Stress load on harvest‐size common carp (Cyprinus carpio L.) just before harvest, during harvest and during the post‐harvest storage were assessed using haematological and biochemical indices. The study was carried out at the 60 ha Dřemliny pond for 28, 7 and 1 day before harvest, during 3‐day harvest and after a 28‐day post‐harvest period. Indices monitored included the relative spleen weight (SSI), erythrocyte count (Er), haemoglobin levels (Hb), haematocrit (PCV), MCV, MCH, MCHC, leucocrit (Bc), differential leucocyte count (leucogram), blood plasma cortisol, glucose, total proteins (TP), cholesterol and chloride. During harvest, a significant decrease of SSI (P<0.05; P<0.01), increase of PCV (P<0.01), decrease of Bc (P<0.01, P<0.05), lymphopenia (P<0.05) and neutrophilia (P<0.01) were observed. A significant increase in the levels of blood plasma cortisol was found 1 day before harvest (P<0.05) due to draining off the pond before harvest itself, hyperglycaemia was observed 1 day before harvest (P<0.05) and during harvest (P<0.01); a decrease, on the other hand, was found in cholesterol and chloride levels (P<0.01). The relationships between oxygen content in water and SSI and MCHC were positive (P>0.05) and between oxygen and glucose were negative (P>0.01). A 28‐day post‐harvest storage returned the indices investigated back to physiological interval of values. Persistently lower levels of Bc, lymphopenia, neutrophilia and lower TP concentrations are indicative of deepening immunosuppression during the post‐harvest storage period. Changes of haematological and biochemical indices during harvest in relation to hypoxia, fish handling and higher stocking rates are also discussed.     

Behavioural response of carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis>, L.) pond stock upon occurrence of hunting great cormorant (<Emphasis Type="Italic">Phalacrocorax carbo sinensis</Emphasis>) flocks

Besides various physiological and biological indices, stress in fish can be expressed directly by changes in their behaviour. Electrofishing point sampling approach based on CPUE (catch per unit effort) was used to evaluate fish density (escapement) into the littoral zones of four Czech ponds as a reaction to the occurrence and hunting activities of great cormorant (Phalacrocorax carbo sinensis) flocks. The behaviour of two-year-old common carp (Cyprinus carpio) before and after cormorant arrival was compared. Significant differences (P < 0.001) in CPUE were recorded in fish density before and after cormorant arrival on all of four ponds under study—Žofinsky: 0.04 ± 0.18 and 22.38 ± 26.87 (mean ± SD), Stary Hospodář: 0.05 ± 0.29 and 25.49 ± 25.45, Žebrákov: 0.16 ± 0.57 and 28.58 ± 24.75 and Travičny: 0.03 ± 0.19 and 17.18 ± 18.20, respectively. The evaluation of fish wounding in the CPUE fish samples proved the proportion of fish injured by cormorant attacks ranging from 3.33 to 18.19% in the ponds under study.     

Effect of Dietary Protein and Lipid Levels on Growth and Body Composition of Spotted Halibut,Verasper variegatus

A 83‐d feeding experiment was undertaken to evaluate the effects of dietary protein and lipid levels on growth and body composition of spotted halibut, Verasper variegatus (initial average weight of 93.0 ± 1.0 g). Nine diets were formulated to contain three protein levels (40, 45, and 50%), each with three lipid levels (8, 12% and 16%). Each diet was randomly fed to triplicate groups of 20 fish per tank in the indoor culture system. Results showed that the survival rate of fish was not significantly affected by protein and lipid levels (P > 0.05). Weight gain, specific growth rate (SGR), and feed intake (FI) significantly decreased with the increasing dietary lipid levels (P < 0.05). Feed efficiency significantly increased while the feed conversion ration significantly decreased with increasing dietary protein levels (P < 0.05). Weight gain, SGR, FI, and feed efficiency of fish fed 50% protein and 8% lipid were significantly higher than that of the other groups. For each level of dietary lipid, the increase in dietary protein resulted in significant increases in whole‐body crude protein (CP) contents (P < 0.05); the increase in dietary lipid caused significant increases in whole‐body crude lipid content and gross energy at each protein level (P < 0.05). The muscle CP, lipid, and gross energy had the same tendency. The results of this study indicated that increasing dietary lipid levels did not result in a protein‐sparing effect. It could be recommended that the proper dietary protein and lipid levels of spotted halibut were 50 and 8%, respectively.     

池塘和稻田养殖模式对金边鲤和建鲤肌肉品质的影响

分析了稻田和池塘养殖模式下金边鲤和建鲤肌肉营养成分、理化特性和质构特性,并进行营养价值评价,评估金边鲤的肌肉品质,为开发和推广金边鲤稻田养殖提供数据依据。结果显示,稻田金边鲤的粗脂肪、粗灰分和系水力均显著高于池塘金边鲤;稻田建鲤和池塘建鲤的基本营养成分除水分外差异均不显著;稻田金边鲤肌肉的硬度、弹性、咀嚼性显著高于池塘建鲤和稻田建鲤,硬度和恢复性显著高于池塘金边鲤,而内聚性显著低于池塘金边鲤、池塘建鲤和稻田建鲤;测定的17种氨基酸中,4组鱼肉的Lys含量均高于WHO/FAO标准和鸡蛋蛋白标准,稻田金边鲤的∑TAA、∑EAA、∑DAA和∑NEAA均高于池塘建鲤和稻田建鲤,且EAA/TAA比值更接近FAO/WHO要求的40%的标准;稻田和池塘金边鲤的EAAI均超过100分,高于稻田和池塘建鲤(82.31～83.36分);测定出的24种脂肪酸中,稻田金边鲤的∑SFA、∑MUFA和DHA+LA+油酸总量均高于其他3组。研究表明,金边鲤和建鲤鱼肉可作为人体优质的赖氨酸源,稻田金边鲤肌肉比建鲤和池塘金边鲤肌肉更富有嚼劲,其肌肉必需氨基酸、不饱和脂肪酸及高度不饱和脂肪酸含量更高,且组成比例更符合人体需求。稻田养殖金边鲤的肌肉品质优势明显,具有较高的产业开发潜力。     

The content of total mercury and methylmercury in common carp from selected Czech ponds

The aim of the present study was to investigate concentrations of total mercury (THg) and methylmercury (MeHG) in the common carp from Czech ponds of Rožmberk, Spolsky, Nezmar, and Velky Bědny. Seven common carps (Cyprinus caprio) from each of the ponds were caught. Muscle tissue, the liver, and the soft and hard roe were used for the tests. Total mercury and methylmercury were found in all the muscle tissue samples examined. Detection limits for total mercury and methylmercury determination methods were 0.001 mg kg^–1 and 0.013 mg kg⁻¹ respectively. Methylmercury levels in the liver and gonads were below the method’s limits of detection. THg and MeHg concentrations in muscle tissues were 0.018–0.063 mg kg^–1 w.w. and 0.019–0.063 mg kg^–1 w.w. respectively. MeHg made up 90–100% of THg in muscle tissues. Total mercury and methylmercury concentrations were significantly (P < 0.05) higher in fish from the Spolsky pond than from the Nezmar pond. MeHg/THg ratios were significantly (P < 0.05) higher in fish from the Rožmberk, Spolsky and Nezmar ponds compared with fish from the Velky Bědny pond.     

Effect of high phosphate fertilization rate on pond phosphate concentrations,chlorophyll <Emphasis Type="Italic">a</Emphasis>, and fish growth in carp polyculture

The effect of different application rates of triple superphosphate (22.4, 44.8, and 67.2 kg P₂O₅ ha⁻¹) was observed on total and available phosphorus concentrations in pond soil, total and filterable orthophosphate concentrations in pond water, chlorophyll a, and fish growth in a carp polyculture system during summer (22–32°C) months to determine the economical dose of P₂O₅. pH, hardness, calcium and alkalinity of soil and water did not differ significantly among treatments (P > 0.05) and were within the desired ranges. Average total phosphorus concentrations in pond soil were not significantly different between treatments but available phosphorus (P > 0.05) in pond soil, total phosphorus (P > 0.001), and filterable orthophosphate (P > 0.0001) concentrations in pond water, chlorophyll a (P > 0.0001), and net fish production (P > 0.01) were significantly higher in fertilized ponds than in controls. Overall, fish yield did not significantly differ among treatments, suggesting that a very high dose of P₂O₅ may not be necessary for high yields. Reducing the dose of P₂O₅ could reduce cost without reducing fish production.     

The use of fenugreek seed meal in fish diets: growth performance,haematological and biochemical parameters,survival and stress resistance of common carp (Cyprinus carpio L.)

The present study was conducted to investigate the effects of fenugreek seed meal (FKSM) on growth performance, blood haematological and biochemical factors, survival and stress resistance of the common carp (2.46 ± 0.06 g) fingerlings. Four practical diets containing 0 (control), 0.5%, 1% and 1.5% FKSM were used to feed fish. Fish were fed on the tested diets at a rate of 3% of body weight for 8 weeks. Results indicated that fish fed the control diet had a significantly lower weight gain, specific growth rate and condition factor compared to the other treatments (P < 0.05). Feed conversion ratio decreased significantly in fish fed diets containing FKSM. There were no significant differences in glucose levels, red blood cell count, haematocrit and haemoglobin between treatment groups and the control group (P > 0.05). Significantly lower white blood cells count was observed in fish treatment with FKSM when compared with the control group (P < 0.05). The cholesterol level in group fed supplemented diet by 1% fenugreek significantly lower than other groups (P < 0.05). Total protein levels were significantly higher in all treatments compared to the control (P < 0.05). No mortality was recorded during the feeding trial. In salinity stress experiment, highest survival rate belong to fish fed supplemented diet by 1% fenugreek. These results indicate that FKSM can be considered as a beneficial dietary supplement for improving the growth performance and blood indices of common carp fingerling.     

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%.     

Increased androgen receptor expression in muscle tissue contributing to growth increase in androgen-treated Nile tilapia

The aim of this study was to investigate the molecular mechanism behind androgen-induced sex reversal and growth increase in Nile tilapia. Three-day-old mixed-sex tilapia juveniles were treated with differential dose (0, 5, 10, 20, 30 mg/kg diet) and duration (0, 15, 30, 45, 60 days) regimes of 17α-methyltestosterone. Treatment regimes 10, 20, 30 mg/kg-30, 45, 60 days showed ~95% males, while 0 mg/kg-0 days (control) showed ~50% males (P < 0.01). Next, tilapia was cultured for 6 months in cistern and pond culture systems with 17α-methyltestosterone-treated diet (10 mg/kg) for three different durations: 0 days (control), 30 days (30-day-treated), and 180 days (throughout-treated). Fish in pond culture showed significantly higher (P < 0.05) final weight compared with tilapia in cistern culture (235.76, 156.82 g, respectively). Both 30-day-treated and throughout-treated fish showed significantly higher (P < 0.05) final weight, length, daily weight gain, specific growth rate, and muscle protein content compared with control fish. The androgen receptor β mRNA and protein expression levels in both 30-day-treated and throughout-treated fish were significantly higher (~twofolds, P < 0.05) compared with hormone-untreated control males. However, there was not much difference for all these parameters among the two hormone-treated groups. This higher growth probably results from an androgen-induced increased ‘androgen-androgen receptor’ mediated anabolic pathway. Serum testosterone concentration of 30-day-treated fish after 6 months was similar to that of control males (0.9 ng/ml). Moreover, culture of 17α-methyltestosterone-treated monosex tilapia was found beneficial than hormone-untreated mixed-sex tilapia culture for maintenance of natural fish diversity in indigenous water bodies.     

Juvenile cobia (Rachycentron canadum) can utilize a wide range of protein and lipid levels without impacts on production characteristics

Two, 6 week feeding trials were conducted to evaluate the impacts of protein and lipid on weight gain, feed efficiency ratio values and biological indices of juvenile cobia (Rachycentron canadum). Utilizing a 2 × 3 factorial design, experimental diets containing two levels of crude protein (CP; 40 and 50%) and three levels of lipid (6, 12 and 18%), providing 14.4, 15.1 and 16.6 kJ available energy/g dry diet (calculated), respectively, were formulated for use in both feeding trials. In the first trial, cobia (initial weight 49.3 g per fish) was randomly assigned to one of the six experimental diets and fed to apparent satiation twice daily. At the end of the first trial, weight gain in cobia was not significantly impacted by protein levels with values ranging from 333% (50% CP) to 353% (40% CP). However, lipid significantly (P < 0.05) affected weight gain with fish fed the diet containing 18% total lipid returning the lowest growth of 293%. Feed efficiency ratio values were not significantly impacted by dietary protein or lipid levels and ranged from 0.46 (50% CP/18% lipid) to 0.51 (50% CP/6 and 12% lipid). Survival was significantly impacted by protein and lipid with fish fed the diets containing 50% CP and 18% lipid having lower (P < 0.05) survival rates of 90%.In the second trial, smaller fish were utilized (7.4 g average initial weight) under identical experimental conditions and dietary formulations. Weight gain was not significantly affected by protein or lipid levels and ranged from 1099% in fish fed the diet containing 40% CP/18% lipid to 1305% in fish fed the diet containing 50% CP/12% lipid. Feed efficiency ratio values, visceral somatic and hepatosomatic indices were significantly affected by protein and/or lipid. Muscle and liver lipid were impacted by dietary lipid (P = 0.0203 and 0.0012, respectively). Muscle protein was significantly impacted by dietary protein levels, while liver protein was affected by both main effects. Dietary protein and lipid had no impact on muscle ash.These data suggest that juvenile cobia can thrive on a wide range of protein and lipid levels, as well as a range of protein to energy ratios. Positive impacts of optimizing the protein component in terms of economic and environmental concerns, coupled with the ability to maintain the rapid growth rates this species are renowned for at lower dietary lipid levels, point towards beneficial consequences of further refinement of commercial cobia production feeds.     

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.     

Dietary Protein Level Affects the Growth Performance of Large Male Genetically Improved Farmed Tilapia,Oreochromis niloticus,Reared in Fertilized Freshwater Cages

An 8‐wk experiment was conducted to evaluate the effects of dietary protein on the growth performance, body composition, and serum biochemical indices of large male genetically improved farmed tilapia (GIFT), Oreochromis niloticus, reared in fertilized freshwater cages. Six semi‐purified diets were formulated, containing 18.05, 22.39, 25.97, 31.62, 35.97, and 39.89% protein (designated as P18, P22, P26, P30, P34, and P38, respectively). Each diet was fed to randomly selected fish (initial mean weight 216.7 g) in four cages. At the end of the experiment, the final body weights varied significantly (P < 0.05), ranging from 520 to 580 g. Fish receiving the P30 diet had the highest final weight value (580.5 ± 5.4 g). Weight gains of fish fed the P26 and P30 diets were significantly higher (P < 0.05) than those fed the P18 and P38 diets. The apparent feed efficiency of fish fed the P18 diet was significantly lower (P < 0.05) than that of fish in the other groups except the P22 group (P > 0.05). The apparent protein efficiency ratio decreased gradually with increasing dietary protein. Whole‐body moisture and ash showed no significant difference (P > 0.05), but protein and fat content were significantly affected by dietary protein level (P < 0.05). No significant differences were found for serum total protein, triglyceride, total cholesterol, glutamic‐oxaloacetic transaminase, and glutamic‐pyruvic transaminase levels among different diets (P > 0.05); only serum glucose level was affected by dietary protein levels (P < 0.05). Second‐order polynomial regression of weight gain suggested 29.3% dietary protein is adequate content for maximum growth of large male GIFT, O. niloticus.     

A comparative study on the apparent digestibility of selected feedstuffs in hybrid catfish (Clarias macrocephalus × Clarias gariepinus) and Nile tilapia (Oreochromis niloticus)

The apparent digestibility (AD) of dry matter (DM), organic matter (OM), crude protein (CP) and essential amino acids (EAA) in five selected feedstuffs was evaluated in hybrid catfish and Nile tilapia. The AD of DM, OM and CP in cassava leaf meal (CLM) was lower (P < 0.05) than in groundnut meal (GNM), soybean meal (SBM), sesame husk meal (SSH) and shrimp head meal (SHM). The AD of DM, OM and CP among GNM, SBM, SSH and SHM was not different (P > 0.05). The AD of most EAA was higher in SSH (P < 0.05) than in CLM, GNM, SBM and SHM. The AD of most EAA among CLM, GNM, SBM and SHM was not different (P > 0.05). The AD of DM and OM in CLM was higher (P < 0.05) in hybrid catfish than in Nile tilapia, while there was no difference in the AD of CP in CLM between fish species. The AD of DM, OM, CP and EAA among GNM, SBM, SSH and SHM did not differ between hybrid catfish and Nile tilapia. In conclusion, there were only small differences in the nutritional properties between the selected feedstuffs in both fish species. Most EAA in the selected feedstuffs were equally well utilized by hybrid catfish and Nile tilapia.     

Growth, reproductive performance, muscle and egg composition in grass carp, Ctenopharyngodon idella (Valenciennes), fed hydrilla or formulated diets with varying protein levels

Growth, reproductive performance, muscle and egg composition were investigated in grass carp, Ctenopharyngodon idella (Valenciennnes), fed hydrilla or formulated diets with varying protein levels. Five experimental diets, with varying levels (20%, 25%, 30%, 35% and 40%) of crude protein (CP), were used. One of the fish groups was fed hydrilla. Fish (44.1±0.3 cm; 913±9 g) were stocked (20 tank^?1) in outdoor concrete tanks (20 × 10 × 1.5 m) in duplicate, and fed to satiation, twice daily, at 09:00 and 17:00 hours for the experimental duration of 360 days. High (P<0.05) weight gain was recorded in fish fed 30% and 35% CP diets. However, values for gonadosomatic index (GSI), egg diameter, relative fecundity (eggs kg^?1 body weight), fertilizability and hatchability (%) were comparable (P>0.05) in fish at ≥25% of dietary protein intake. Hydrilla‐fed fish exhibited lower (P<0.05) values for the measured parameters. Crude protein content in muscle increased with dietary protein level. Highest (P<0.05) muscle protein was obtained in fish fed 35% CP diet. Muscle fat was comparable (P>0.05) among fish receiving formulated diets. Ash content was not significantly (P>0.05) different among fish of different dietary groups. Moisture content in fish fed formulated diets, with the exception of 20% CP diet, did not vary significantly (P>0.05). Eggs of fish fed formulated diets contained higher CP and fat contents than those of hydrilla‐fed fish. High (P<0.05) moisture content was noted in the eggs of hydrilla‐fed fish. Ctenopharyngodon idella fed formulated diet, with a minimum of 25% CP, showed better reproductive performance than those fed hydrilla.     

Growth performance,feed utilisation and biological indices of Tra catfish (<Emphasis Type="Italic">Pangasianodon hypophthalmus</Emphasis>) cultured in net cages in pond fed diets based on locally available feed resources

The feeding experiment was conducted to evaluate the efficacy of locally available feed resources for Tra catfish (Pangasianodon hypophthalmus) cultured a series of 21 hapa net cages installed in the earthen pond during a 4-month period. The reference diet contained fish meal as the main crude protein (CP) source, whilst in the seven test diets 20–100 % of the fish meal CP was replaced with CP from local feed ingredients: groundnut cake (GNC), cassava leaf meal (CSLM), sweet potato leaf meal (SPLM), soybean meal (SBM), golden apple snail meal (GASM) and shrimp head meal. There were differences (p < 0.05) among diets in final body weight, total weight gain, daily weight gain, specific growth rate, viscera-somatic weight (VSI%), hepato-somatic index (HIS%) and intra-peritoneal fat (IPF%). The respective values for the shrimp head meal diet were numerically highest, followed in descending order by the reference, GASM, GNC, SPLM, CSLM and SBM diet. Food conversion ratio, fish survival rate, total feed intake, feed utilisation, fish fillet and kidney proportions did not differ among the reference and test diets (p > 0.05). However, the viscera-somatic, hepato-somatic, kidney and intra-peritoneal fat indices differed among treatments (p < 0.05). These data show that fish meal protein can be replaced with protein from locally available plant and animal feed ingredient resources in feed cultured in net cages in pond for Tra catfish fingerlings in effectively compromising growth performance, feed utilisation or carcass traits of fish.     

Tuna viscera protein hydrolysate: nutritive and disease resistance properties for Persian sturgeon (Acipenser persicus L.) larvae

The effect of fish protein hydrolysate (FPH) on the growth, feed utilization, digestive enzymes, gut microflora and resistance to bacterial challenge in Persian sturgeon (Acipenser persicus) larvae during a 45‐day feeding trial has been investigated. Artificial diets containing different levels of tuna visceral protein hydrolysate (PH0, PH10, PH25 and PH50) and live foods (Artemia: 5 days, Daphnia: 40 days) were fed to Persian sturgeon larvae. Larvae fed on the PH10 and PH25 had growth, feed utilization, protein content and trypsin activity significantly better than PH0 and PH50 groups (P < 0.05). Condition factors, survival rate and pepsin activity were not significantly different (P > 0.05). Brush border membrane enzymes to cytosolic enzyme ratio revealed that maturation had been occurred in 41 days post hatch (dph) at moderate FPH levels. In 54 dph larvae, this ratio was not affected by the level of FPH in the diet. No significant differences were observed in the total number of gut microflora or in the resistance to Aeromonas hydrophila (P > 0.05), whereas lactic acid bacteria was significantly higher in PH50 (P < 0.05). The results of this study show that application of moderate levels of FPH in Persian sturgeon diets could enhance larvae performance due to the early maturation in intestinal.     

Effects of body weight on the growth and physiology of Salmo salar L. during smoltification

To study the effects of body weight on growth and physiological response mechanism of S. salar, fish of three average body weights were selected: 30.25 ± 2.12 g (SW1), 24.27 ± 1.59 g (SW2) and 18.05 ± 2.46 g (SW3). Condition factor, daily weight gain and feed conversion efficiency were significantly higher in the SW2 group compared with the other treatment groups (P < 0.05). Food conversion ratio decreased with increasing body weight, and weight and specific growth rate of body length were highest in the SW2 group (P < 0.05). Larger fish (SW1 and SW2) had higher haemoglobin concentration and number of red blood cells. The number of white blood cells, lymphocytes and neutrophils were greatest in the SW3 group (P < 0.05), suggesting that these fish had strong resistance to disease. The content of total protein, albumin and urea were significantly higher in the SW2 group compared with other groups (P < 0.05). The concentration of total cholesterol and triglyceride increased with increasing body size (P < 0.05). Hormone (T3 and T4) levels first increased significantly and then decreased in fish of various sizes (P < 0.05), and the concentration of cortisol rose, fell and then rose again in SW1 and SW2 groups. Light affected the endocrine activity of S. salar by influencing the growth performance of the fish, and smaller sized fish exhibited decreased smoltification rate and a reduced success rate of smoltification. Based on these findings, S. salar weighing about 24 g were chosen to begin the process of smoltification.     

Seasonal dynamics of fish assemblage in a pond canal

The annual dynamics of fish assemblage in a pond-connecting canal of a South Moravian pond aquaculture facility was studied to reveal potential assemblage effects on pond stocks and vice versa. The species richness of fish assemblage and seasonal dynamics of its development were predominantly dependent upon the fish stock of the interconnected ponds (particularly due to escapees during the period of pond harvesting), which contributed to a considerable increase of commercial fish species occurrence. Using a seasonal parameter, the season proved to have a major impact on fish assemblage dynamics (r = −0.71, P < 0.001). Spring samples were dominated by commercial fishes of aquaculture origin (mainly Cyprinus carpio). Occurrence of several fish species originating from the wild (bleak, Alburnus alburnus, chub, Leuciscus cephalus and roach, Rutilus rutilus) was also reported. The pond canal was found to be an important reservoir site of persistent survival and potential subsequent spreading of some undesirable alien fishes such as topmouth gudgeon (Pseudorasbora parva) and gibel carp (Carrasius auratus). Moreover, more attention should be paid to the potential negative impacts of all fishes of aquaculture origin upon the natural ecosystem and to the adverse effects due to the immigration of wild fish into aquaculture pond farming units.     

Taurine synthesis via the cysteic acid pathway: effect of dietary cysteic acid on growth,body taurine content,and gene expression of taurine-synthesizing enzymes,growth hormone,and insulin-like growth factor 1 in Japanese flounder Paralichthys olivaceus

Here, we investigated the effect of dietary cysteic acid on the growth performance, sulfur amino acid content, and gene expression levels of taurine-synthesizing enzymes, growth hormone (GH), and insulin-like growth factor 1 (IGF-1) in Japanese flounder Paralichthys olivaceus. Juvenile flounder (0.9 g) were fed one of four diets for 30 days: with 0.25, 0.5, or 1.0% cysteic acid (C0.25, C0.5, C1.0) supplementation and without supplementation (control). Fish in the C0.25 and C0.5 groups showed significantly better growth than those in the control group (P < 0.05). Body taurine content was significantly higher in C0.25, C0.5, and C1.0 fish than in control fish (P < 0.05). Although there was no significant difference in gene expression levels of taurine-synthesizing enzymes and GH among groups (P > 0.05), the expression level of IGF-1 in C1.0 fish was significantly higher than that in controls (P < 0.05). Our results suggest that Japanese flounder can synthesize taurine from cysteic acid, that dietary supplementation with up to 0.5% cysteic acid promotes fish growth, and that dietary cysteic acid can affect the GH-IGF axis in Japanese flounder. These findings thus highlight the importance of the cysteic acid pathway for taurine synthesis and growth in this species.