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Abstract
A study was conducted from January-May 2007 to know some biological aspects i.e. gonadosomatic index (GSI), gamete sizes (egg diameter and sperm-head length), fecundity, condition factor (CF), relationship of body weight-fecundity and ovary weight-fecundity of Thai koi Anabas testudineus. The highest gonadosomatic index (19.50 ± 0.54), ova diameter (654.10 ± 6.37 pm) and sperm head-length (3.18 ± 0.08 pm) were found in 17th April. The mean fecundity was estimated to be 5,53,708 ± 41,041/kg with a range between 1,13,285 and 10,25,423/kg. The ovary weight ranged from 2.86 to 20.50g/100g with a mean of 11.16 ± 0.696g/100g, whereas the average numbers of eggs/g body and ovary weight were 526 and 4480 respectively. The highest condition factor (CF) 1.005 ± 0.12 indicated good health condition of fish in April than in the other months. The regression analysis showed that the relationship between body weight-fecundity and ovary weight-fecundity were linear. Co-efficient of correlation (r) of ovary weight-fecundity was highly significant (P<0.01) and stronger than the correlation (r) of body weight-fecundity. From the results it can be concluded that the peak spawning period of Thai koi might be in April.