No abstract

The feeding trials were carried out with freshwater crayfish (Procambarus clarkii) to evaluate the three feed stimulants betaine (Bet), squid extract (SE) and squid meal (SM) upon fish meal (FM) diets or biofeed (BF) diets in which FM were partially replaced by BF. Results showed the three feed stimulants had no significant effect on growth. By the relative concentration of markers in the faeces and diets, the preference for each diet was estimated, and the best stimulant was the mixture of Bet, SE and SM. As FM replaced by BF increased, added with the mixture, the relative weight gain showed an increasing trend, but decreased significantly by 30% replacement. With the substitution increasing, trypsin activities increased, whereas decreased too upon 30% substitution. Less than 30% replacement, there was no significant effect on muscle proximate composition, intestine amylase activities and serum haemocyanin contents, except the drop of lipid. The results indicated that the mixture of Bet, SE and SM could perform well as a feed stimulant. And with the addition of the mixture, FM in the diet could make about no more than 20% saving without any adverse effects. 3 Biofeed (g kg À1 ): crude protein 437, crude lipid 58, calcium 17, phosphorus 16.7, moisture 120 and ash 170. 4 Other components (g kg À1 ): rapeseed meal 100, soybean meal 93, vinasse 80, cottonseed meal 40, corn protein 60, flour 180, soybean oil 18, fish oil 18, mineral mixture 5, vitamin mixture 5, calcium dihydrogen phosphate 15, compound phosphatide 20, moult hormone 1, choline 1, dextrin 10, gelatine 40 and markers: diets of the same group (fish meal or biofeed) were marked with 100 mg kg À1 of the oxides of rare earth element, respectively (

No abstract

The effects of five salinities (5, 10, 20, 30, and 35‰) on the survival, growth, body composition, oxygen consumption, and ammonia excretion of juvenile Spotted Scat Scatophagus argus (initial body size 3.3–3.4 cm body length and 2.0–2.3 g; final body size: 5.5–5.6 cm body length and 9.2–9.8 g) were studied. Salinity did not affect survival (>94%) or oxygen consumption rate (OCR) significantly, but it did affect growth, ammonia excretion rate (AER), and body composition. The growth rate was related to the combined effect of food intake (3.1–3.2%/d) and feed conversion efficiency (56.8–60.2%). The highest slope of the body length/weight with rearing time regression equation at 5‰ salinity was 0.0333/0.1137, which indicated that the growth rate of the fish at 5‰ salinity was higher than that of those at the other salinities for 70 d at 24.4 ± 0.4°C. The ammonia excretion rate decreased significantly with the increase of salinity. Low O:N ratios (5.6–19.2) occurred at salinities ranging from 5‰ to 35‰, indicating a protein‐dominated catabolism. Salinity affected crude protein content significantly, and high salinity was beneficial to protein deposition. The results indicated that juvenile Spotted Scat could adapt to a wide range of salinity, from 5‰ to 35‰. However, it is recommended that juveniles be cultured at low salinity (5‰).

A laboratory experiment was undertaken to analyze the effects of salinity on growth, body composition, oxygen consumption, and ammonia excretion of anadromous American shad (Alosa sapidissima) juveniles. Results showed the best survival rate occurred at 5‰ and 15‰. The relative weight gain and the specific growth rate declined as salinity increased. However, feed conversion rate increased with increasing salinity. Oxygen consumption rates showed a parabolic relationship in relation to salinity. From the quadratic relationship (y= -0.0004x2+0.0166x+0.319; R2=0.801; P<0.05), the highest oxygen consumption rate occurred at a salinity of 20.75‰. The ammonia excretion ratio decreased significantly as salinity increased from 10‰ to 15‰. No further differences were observed in salinities ranging from 15‰ to 40‰. There were no significant influences of salinity on whole body protein and moisture content. Lipid content declined as salinity increased. Results indicate that an appropriate increase in salinity was beneficial to the culture of American shad juveniles. The optimal salinity for American shad juveniles ranged from 15‰ to 20‰.