Abstract:
Forty days-old and a hundred days-old crabs (Portunus pelagicus) from culture were used for the study. External carapace width and total weight of them were 4.1±0.1 cm and 5.8±0.2 cm, 10.5±0.3 g and 56.5±0.6 g, respectively. The experimental crabs were raised in a cubic meter concrete pond at 30 ind/m2 in 30 ppt. Pellet in cylinder form of 2.5 and 4 mm in length with 1.5 mm, 2 mm in diameter at four protein levels of 30%, 35%, 40% and 45% using completely randomized design were respectively used for forty days-old and a hundred days-old crabs. Feed with rations of 5% body weight of crab were applied in feeding tray, three times a day for 60 days. Three replications were done. Dead or molted crabs were daily checked. Every 15 days, the external carapace width and total weight of an experimental crab of each treatment were individually examined. The data of external carapace width, total weight molt frequency, survival rate and feed conversion ratio were analyzed by one-way ANOVA and compared means using Duncans New multiple range test at 95% level of confidence. Every five days, water quality as pH, alkalinity, temperature, dissolved oxygen, ammonia and nitrite were checked throughout the experimental period.
The results found that 40% and 35% protein in pellet was respectively suitable for 40-100 and 100-160 days-old crab. Growth in terms of % external carapace width (%ECWG) and % total weight gain (%TWG) , survival rate and feed conversion ratio (FCR) of 40 days-old crab fed on 40% and 45% protein were not significant different (p>0.05). But growth parameter and survival rate of both levels were significantly higher (p<0.05) than those of at 35% and 30% protein. Growth parameter and FCR of crab fed on 35% protein were also significantly (p<0.05) higher and lower than those of at 30% protein.
Percentage of ECWG and TWG of 100 days-old crab fed on 35%, 40% and 45% protein were not significant different (p>0.05). But %ECWG, %TWG and % survival rate of these protein levels showed significantly higher (p<0.05) than those fed on 30% protein. FCR of crab fed on 40% and 45% proteins was not significantly (p>0.05) different. Both level was significantly (p<0.05) lower than that of 30% protein. FCR of crab fed with 35% protein showed significantly (p<0.05) lower than that of 30% but it was not significantly (p>0.05) different with 40% protein. Molting frequency among treatments in each experiment was not