Biology of the exotic fish, Thai climbing perch, Anabas testudineus (Bloch) was studied for one year period from November 2016 to October 2017. Twenty four morphometric characters of 180 fishes were used in morphometric study. The relationships between dependent (Y) and independent (X) variables using least square method fitted straight line equation Y= a+bX.  All relationships were linear, positive and significant at 0.01 level. Morphometric characters were categorized into three categories, narrow, intermediate and wide ranges. In the % of Total length, 4 characters were found in the narrow range (genetically controlled, non plastic), 10 characters as intermediate (environmentally controlled, plastic) and 4 characters as wide range (hydro-biologically controlled). In the % of Head length, 6 characters were found under wide range and none were found under narrow and intermediate ranges. Length (TL)-Weight (W) relationship of 380 fish of combined sexes was found to be curvilinear, W= 0.041TL2.631 and linear, logW= -1.377+ 2.6315logTL. The values of regression co-efficient (b) ranged from 2.51 to 2.9 (β±0.37004) at 95% confidence limit (P<0.05) and growth was found to be negative allometric. Monthly relative condition factor (Kn) showed no significant variation and ranged from 0.9797 (May 2017) to 1.0145 (Jan 2017) with a mean of 0.999±0.06. Stomach contents and fish total length (TL) vs gut length (FGL) (FGL= 0.9075TL1.02044) relationship and their ratio (1:0.92063) showed that the fish was carnivorous and consumed mainly animal origin food. Yearly sex ratio was 1:1.37 (ϰ2 = 5.29, DF=1, n=123), which was significantly (P<0.05) different from the hypothetical male and female ratio 1:1, whereas, monthly sex ratio was insignificant (P>0.05). Female attained sexual maturity at 12.1 cm of total length. Fecundity varied from 15478 eggs to 38745 eggs. The mean number of eggs was 29562.6±6306.43 for a fish of mean total length 13.1±6.632 cm, mean body weight 41.287±31.771 g, mean ovary length 4.45±3.45 cm and mean ovary weight 3.787±3.047 g. Fecundity factor was 645.501±792.106. The relationships between fecundity in relation to total length, body weight, ovary length and ovary weight were linear and significant (P<0.05).

Key words: Biology, Anabas testudineus, morphometrty, length-weight relationship, food and feeding, reproductive biology

Introduction Climbing perch (Koi) is considered as a valuable fish item of diet for sick and convalescents. In Bangladesh two types of Koi viz. indigenous (natural) and exotic (cultured) are found very frequent. Among the exotic perch ‘Thai Koi’, first introduced to Bangladesh from Thailand in 2002, ensures high growth rate and productivity. It can withstand bad environmental conditions such as low oxygen, wide variation of temperature and other poor quality of water due to presence of air breathing respiratory organ. In late 1980s, the catches of the native climbing perch had drastically declined from open waters due to various man-made and environmental changes in inland water bodies. So, fry production technology through artificial propagation was developed in hatchery condition by the Bangladesh Fisheries Research Institute (BFRI).