Search

An 8-week experiment was designed to determine the optimum dietary iron requirement of juvenile cobia Rachycentron canadum (mean initial weight, 15.89 ± 0.84 g) with iron sulphate (Fe SO4•7H2O) and iron methionine (FeMet) as iron sources, using a semi-purified diet based on casein and white fish meal as the protein sources. The basal diet was supplemented with 0, 30, 60, 120, 240 and 480 mg iron kg−1 dry diet from either Fe SO4 or FeMet, respectively. Survival was not significantly affected by the all dietary treatment. Weight gain ( WG), feed efficiency ( FE), serum catalase activity ( SCAT), and haemoglobin were significantly affected by any of the dietary treatments from both of two iron sources. Based on broken-line regression analysis of WG, FE and SCAT, a minimum requirement for dietary iron was recommended to be 80.5-94.7 mg kg−1 from Fe SO4 and 71.3-75.1 mg kg−1 from FeMet. Iron supplement to the basal diet had no significant effect on haematocrit, erythrocyte count, iron concentration in whole body and fillet. Our experiment also showed that the bioavailability of FeMet and Fe SO4 to juvenile cobia was similar for WG and FE, and the relative bioavailability of FeMet and Fe SO4 to juvenile cobia was 275% for maximum SCAT. [ABSTRACT FROM AUTHOR]

A 10-week feeding trial was conducted to determine the optimal requirement of cobia ( Rachycentron canadum Linneaus) for dietary ascorbic acid (AA). Graded levels of L-ascorbyl-2-polyphosphate (LAPP) were supplemented in basal diet to formulate six semi-purified diets containing 2.70 (the control diet), 8.47, 28.3, 80.6, 241 and 733 mg AA equivalent kg diet, respectively. Each diet was randomly fed to triplicate groups of fish in flow-through plastic tanks (300 L), and each tank was stocked with 25 fish with average initial weight of 4.59 ± 0.36 g. Observed deficiency signs included poor growth, higher mortality and lower feeding rate (FR) in the fish of the control group. Fish fed the control diet had significantly lower weight gain (WG), lower feed efficiency ratio (FER) and lower tissue AA concentrations in fish liver and muscle. With the increase of dietary AA, the survival, WG, FER, hepatic and muscular AA concentrations of cobia significantly increased and then levelled off. The dietary AA requirement of cobia was estimated to be 44.7 mg kg based on WG, 53.9 mg kg or 104 mg kg based on either hepatic or muscular AA concentration, respectively. [ABSTRACT FROM AUTHOR]

This experiment was conducted to evaluate the effect of different levels of dietary phospholipid (PL) on growth, survival and nutrient composition of 25 days posthatch cobia Rachycentron canadum (0.4 g initial wet weight). For 42 days, fish were fed fish meal and protein hydrolysate based diets containing four PL levels (0, 20, 40 and 80 g kg−1dry matter: purity 97%) and phosphatidylcholine purity was 60%. All diets were isonitrogenous and isolipidic by regulating the fish oil and maize oil levels. Weight gain (2601–10892%), specific growth ratio (7.82–11.18) and survival (49–100) were significantly affected by dietary PL. Intraperitoneal fat ratio (0.19–0.74) and hepatosomatic index (2.67–3.08) increased with dietary PL level. The effect of dietary PL levels on the chemical composition of tissues was significant only for whole body and liver. The contents of plasma total cholesterol (2.47–3.77 mmol L−1) and PL (1.03–2.97 mmol L−1) increased with an increase in dietary PL. In conclusion, in our study survival and growth continued to increase even at the highest PL levels used (80 g kg−1); therefore optimal dietary PL levels may well exceed 80 g kg−1 for early juvenile cobia requirement. It also indicated from the experiment that PL could affect lipid deposition and resulted in a higher lipid level in fish tissue. [ABSTRACT FROM AUTHOR]

A study was conducted to determine the effects of dietary phospholipid (PL) levels in cobia ( Rachycentron canadum) larvae with regard to growth, survival, plasma lipids and enzymes of lipid metabolism. Fish with an average weight of 0.4 g were fed diets containing four levels of PL (0, 20, 40 and 80 g kg−1dry matter: purity 97%) for 42 days. Final body weight (FBW), weight gain (WG) and survival ratio were highest in the 8% PL diet group and mortality was highest in PL-free diet group. We examined the activities of lipoprotein lipase (LPL) and hepatic lipase (HL) in liver, lecithin-cholesterolacyltransferase (LCAT) in plasma as well as plasma lipids and lipoprotein. LCAT activity showed a decrease of more than two-fold in PL-supplemented diet groups compared with the PL-free diet group. HL activity was highest in the 8% PL diet group and the other three groups showed no difference. LPL activity was significantly higher in the PL-supplemented diet groups than in the PL-free diet group. The dietary intervention significantly increased plasma phospholipids and total cholesterol (TC) levels, and the higher free cholesterol (FC) level contributed to the TC level. However, the fish fed PL exhibited a significantly decreased plasma triglyceride (TG) level. The lipoprotein fractions were also affected significantly by the PL. The PL-supplemented diet groups had significantly higher high-density lipoprotein (HDL) compared with the PL-free diet group, but showed a marked decrease in very low-density lipoprotein (VLDL). The results suggested that PL could modify plasma lipoprotein metabolism and lipid profile, and that the optimal dietary PL level may well exceed 80 g kg−1 for cobia larvae according to growth and survival. [ABSTRACT FROM AUTHOR]

An 8-week feeding experiment was conducted in floating cages (1.5 × 1.0 × 2.0 m) to determine the potential use of defatted soybean meal (roasted and solvent-extracted) as a partial replacement of fishmeal in the isonitrogenous (approximately 450 g kg−1 CP [crude protein]) diet for juvenile cobia with an initial average weight of about 8.3 g. Diets were formulated to include 0, 100, 200, 300, 400, 500 and 600 g kg−1 (diets D0, D10, D20, D30, D40, D50 and D60, respectively) of fishmeal protein being substituted by defatted soybean meal without methionine supplementation. The results showed that weight gain rate decreased significantly when the replacement level of fishmeal protein was increased from 400 g kg−1 to 500 g kg−1, and the D60 diet was the lowest in all groups. These results indicate that up to 400 g kg−1 of fishmeal protein can be replaced by defatted soybean meal without causing significant reduction in growth. Feed conversion ratio (FCR) and protein efficiency ratio (PER) were significantly affected by the replacement level of fishmeal protein being substituted by defatted soybean meal, when the replacement level of fishmeal protein was 200 g kg−1 (diet, D20), FCR was the lowest and PER was the highest. There were no significant differences in the moisture, lipid, crude protein and ash content in whole body and muscle, while lipid content in liver increased as the dietary soybean meal replacement levels increased. There were significant differences in haemoglobin, haematocrit, red blood cell, plasma glucose and triglyceride concentration in fish fed diets with different soybean meal replacement levels. Results of this trial indicated that the optimum level of fishmeal protein replacement with defatted soybean meal, determined by quadratic regression analysis was 189.2 g kg−1, on the basis of maximum weight gain. [ABSTRACT FROM AUTHOR]