| Pseudobagrus ussuriensis is one of the most important indigenous species in the northeast of China. Pseudobagrus ussuriensis is a Siluriformes species with high potential for aquaculture exploitation in China due to its excellent taste, high market value, high resistance against diseases and availability of reproduction technology. So far, no nutritional studies have been conducted to determine the nutritional requirements of this fish, and there are no commercially available feeds specifically formulated for this fish, which is a limiting factor for the development of this species reared in aquaculture. The present study was carried out to compare the nutritional composition of farmed and wild Pseudobagrus ussuriensis muscles, to evaluate the optimum protein and energy levels, lysine and methionine requirements, and utilization of soybean meal of Pseudobagrus ussuriensis for developing cost-effective and nutritionally balanced diets. The Results of the study are presented as follows:1. Comparative study of nutritional composition of farmed and wild Pseudobagrus ussuriensis musclesThe nutritional composition of the muscle of wild Pseudobagrus ussuriensis and farmed fish were compared. The lipid content of the farmed fish was significantly higher, while moisture content was significantly lower, than those of the wild fish (P<0.05). Pseudobagrus ussuriensis protein has a well-balanced amino acid composition. The amino compositions of the two groups are also including16kinds of amino acids (tryptophan was not measured). The percentages of total amino acids, total essential amino acids, total nonessential amino acids and total delicious amino acids were significantly higher in the wild than those in farmed fish. The ratios of WEAa/WTAA (42.78%～43.02%) and WEAA/WNEAA (85.52%～87.74%) were comparable to the reference values of40%and above60%recommended by FAO/WHO. According to the amino acid scores, methionine and cystine would has been described as the first limiting amino acid, and Lys had the highest score for the proteins in both wild and farmed Pseudobagrus ussuriensis. Total saturated fatty acids (SFAs) were higher in the wild fish comparing to cultured fish, whereas its total polyunsaturated fatty acids (PUFAs) was lower, and monounsaturated fatty acids (MUFAs) did not differ significantly between farmed and wild fish. This study shows that Pseudobagrus ussuriensis under investigation have high nutritional qualities and are good protein resources.2. Effects of dietary protein and lipid levels on growth, feed utilization and body composition in Pseudobagrus ussuriensis fingerlingsAn8-week feeding trial was conducted to investigate the optimum dietary protein and lipid levels for growth, feed utilization and body composition of Pseudobagrus ussuriensis fingerlings (initial weight:3.40±0.01g). Twelve diets containing four protein levels (350,400,450and500g kg-1crude protein) and three lipid levels (50,100and150g kg-1crude lipid) were formulated. Fish were randomly allotted to36aquaria (1.0x0.5x0.8m) with25fish to each glass aquarium. Fish were fed twice daily (08:00and16:00) to apparent satiation. The results showed that weight gain and specific growth rate (SGR) decreased with increasing dietary lipid level from50to150g kg-1at the same dietary protein level. Fish fed the diets containing150g kg-1lipid exhibited higher FCR (p<0.05), lower protein efficiency ratio (PER) and nitrogen retention efficiency (NRE) relative to fish fed the diet containing50and100g kg-1lipid. Weight gain and SGR significantly increased with increasing dietary protein from350to450g kg-1at the same dietary lipid level, and even a little decline in growth with the further increase of dietary protein to500g kg-1. PER decrease with increasing dietary protein and lipid levels (Table3). PER of fish fed the350,400,450g kg-1protein diet with150g kg-1lipid was significantly (P<0.05) lower than that of fish fed the50g kg-1or100g kg-1lipid diet. Daily feed intake, NRE and PER were significantly affected by both dietary protein and lipid levels (p<0.05), and tended to decrease with increasing dietary protein and lipid levels.No significant differences among treatments were detected for moisture content in whole body samples (P>0.05). Whole body protein content increased as protein levels increased and lipid levels decreased. Whole body lipid and muscle lipid content increased with increasing dietary lipid level, and decreased with increasing dietary protein at each lipid level. There were no significant difference in condition factor and viscerosomatic index among fish fed the diets. Hepatosomatic index was affected by dietary lipid level (P<0.05), and increased with increasing dietary lipid level at the same protein level. No significant differences among treatments were detected for moisture, protein and ash content in muscle samples (p>0.05). Muscle protein content increased as protein levels increased at the same lipid level. Muscle lipid content was affected by dietary protein and lipid level (P<0.05), and increased as lipid levels increased and protein levels decreased.3. Dietary lysine requirement of juvenile Pseudobagras ussuriensisAn8-week feeding experiment was conducted to estimate the dietary lysine requirement of juvenile Pseudobagras ussuriensis with an initial average weight of0.60g reared in indoor flow-through and aerated aquaria (1.0x0.5x0.8m3). Six isonitrogenous and isolipidic diets containing six levels of dietary lysine levels ranging from1.34%to4.84%(dry weight) at about 0.7%increments were formulated. Equal amino acid nitrogen was maintained by replacing lysine with nonessential amino acid mixture. Triplicate groups of50fish were fed to apparent satiation by hand twice daily (08:00and16:00). No significant differences were observed in survival rates of fish (86.67%～92.67%), but specific growth rate (SGR), weight gain (WG), feed conversion ratio (FCR) and protein efficiency ratio (PER) were significantly affected by different dietary lysine levels (P<0.05). Weight gain (WG), SGR and PER increased, while FCR decreased with increasing dietary lysine level up to3.44%(8.43%of the dietary protein), and then leveled off. The whole body and muscle crude protein contents increased significantly with dietary lysine levels from1.34%to3.44%(P<0.05), and decreased with dietary lysine levels from3.44%to4.84%(P>0.05). Moisture and lipid content in whole body, moisture content in muscle were not affected by dietary lysine level. The muscle lipid contents increased significantly with dietary lysine levels from1.34%to2.74(P<0.05), and thereafter, remained nearly the same. The hepatosomatic index was negatively correlated with dietary lysine levels, but no significant differences were observed. CF and VSI were significantly affected by dietary lysine levels. CF of1.34%treatments were significantly lower than the other treatments (P<0.05). VSI of3.44%and4.14%treatments were significantly lower than those of fish fed diets1.34%,2.04%,2.74%and4.84%group (.P<0.05). Broken-line analysis on the basis of weight gain showed that the dietary lysine requirement of juvenile Pseudobagras ussuriensis was3.38%of dry diet (8.31%dietary protein); Quadratic regression analysis of PER against dietary lysine levels indicated that the optimal dietary lysine requirement for maximum growth and feed utilization of juvenile Pseudobagras ussuriensis is3.91%of dry diet (9.61%dietary protein).4. Dietary methionine requirement of juvenile Pseudobagras ussuriensisAn8-week feeding experiment was conducted to estimate the dietary methionine requirement of juvenile Pseudobagras ussuriensis with an initial average weight of0.60g reared in indoor flow-through and aerated aquaria (1.0x0.5x0.8m3). Six isonitrogenous and isolipidic diets containing six levels of dietary methionine levels ranging from0.55%to2.05%(dry weight) at about0.3%increments were formulated at a constant dietary cystine level of0.25%. Equal amino acid nitrogen was maintained by replacing lysine with nonessential amino acid mixture. Triplicate groups of50fish were fed to apparent satiation by hand twice daily (08:00and16:00). No significant differences were observed in survival rates of fish (84.67%～91.33%), but specific growth rate (SGR), weight gain (WG), feed conversion ratio (FCR) and protein efficiency ratio (PER) were significantly affected by different dietary methionine levels (P<0.05). WG, SGR and PER increased, while FCR decreased with increasing dietary methionine level from0.55%to1.15%(P<0.05), however, with further increase in dietary methionine level from1.15%to2.05%, WG, SGR and PER significantly decreased, while FCR increased (P<0.05). The whole body and muscle crude protein contents increased significantly with dietary methionine levels from0.55%to 1.15%(P〈0.05), and decreased with dietary methionine levels up to2.05%. The whole body and muscle lipid contents increased significantly with dietary methionine levels, and thereafter decreased. Moisture and ash content in whole body were not affected by dietary methionine level. The muscle moisture content of1.15%group was significantly lower than the1.45%group (P〈0.05). The muscle ash content of1.45%,1.75%and2.05%group were significantly higher than the0.85%and1.15%group (P〈0.05). CF increased with increasing dietary methionine levels from0.55%to1.15%(P〈0.05) and then decreased with further increase to2.05%(P>0.05). HSI of0.55%,0.85%,1.15%and1.45%groups were significantly higher than those of fish fed diets1.75%and2.05%groups (P〈0.05). VSI of0.55%,0.85%and1.15%groups were significantly higher than those of fish fed diets1.45%,1.75%and2.05%groups (P〈0.05). Quadratic regression analysis of weight gain and PER gainst dietary methionine levels indicated that the optimal dietary methionine requirement for maximum growth and feed utilization of juvenile Pseudobagras ussuriensis were1.42%and1.39%dry diet (3.51%and3.44%dietary protein), respectively in the presence of0.25%cystine.5. Fish meal replacement by soybean meal in diets for juvenile Pseudobagras ussuriensisAn8-week feeding experiment was conducted in indoor culture system to evaluate the effects of replacing fish meal with soybean meal (SBM) in feeds for juvenile Pseudobagras ussuriensis. Triplicate groups of juvenile Pseudobagras ussuriensis (initial weight of0.5g) were fed one of eight experimental diets which were formulated to replace FM protein by SBM at0%,10%,20%,30%,40%,50%or60%(designated as SO, S10, S20, S30, S40, S50or S60, respectively). To investigate the effects of supplementation with crystalline amino acid mixture (CAA) to balance Diet S60, one diet was formulated to add0.3%methionine (SM60). Growth, feed utilization were significantly affected by dietary SBM replacement level (P<0.05). Weight gain (WG), specific growth rate (SGR) and protein efficiency ratio (PER) linearly decreased with increasing SBM replacement level from0to60%, however, there were no significant differences in WG, SGR and PER between fish fed the control diet and feeds in which SBM replaced10to40%of the fish meal (P>0.05), but fish fed the diets S50and S60had lower WG, SGR and PER than the diet SO (P〈0.05). Supplementation with CAA improved growth and feed efficiency, however, there were no significant differences in growth between fish fed the diet S60and diet SM60(P>0.05), and significantly lower than those in fish fed diet SO. Feed conversion ratio (FCR) had an opposite trend with WG and SGR. There was no significant difference in feeding intake (FI) among fish fed the different diets. Moisture and ash content in whole body were not affected by dietary SBM replacement level. The muscle moisture content of diet SO was significantly lower than the other groups (P〈0.05). The whole body and muscle protein contents decreased with the increase of dietary SBM level, and fish fed the feeds in which SBM replaced0to50%of the fish meal had higher protein content than that of fish fed the diets S60and SM60(P〈0.05). The whole body and muscle lipid contents increased with increasing dietary SBM level, and S60and SM60groups were significantly higher than the other groups (P<0.05). The CF was inversely correlated with the SBM replacement level, but no significant difference was found among the dietary treatments. Fish fed the diets S60and SM60had higher VSI and HSI than those of fish fed the diets in which0to50%of the fish meal was replaced (P<0.05), and no significant difference in VSI and HSI among fish fed the diets S0-S50was found. The ADC of protein and dry matter of the diet S50and S60were significantly lower than that of the other diets (P0.05), while no significant differences were found among the other diets (P>0.05). The ADC of phosphorus significantly increased with an increase of SBM incorporation in the diet (P<0.05). Phosphorus excretion significantly decreased with increasing levels of SBM replacement (P<0.05), while phosphorus retention increased with increasing levels of SBM replacement from0to60%. Fish fed the diets SO and S10had lower nitrogen excretion than those of fish fed the diets in which20to60%of the fish meal was replaced (P<0.05). Fish fed the diets S30and S60had lower nitrogen retention than those of fish fed the other diets (P<0.05). The results of this study show that SBM is an acceptable ingredient to replace40%of fish meal in Pseudobagras ussuriensis diets, but that higher dietary levels reduce fish performance under the experimental conditions used in this study. |
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