Biology of Koi (Anabas testudineus) Intoduction: A. testudineus, locally called koi, is an economically important fish species in Bangladesh. It inhabits fresh and brackish waters of the Indian subcontinent and southeast Asia. The natural food spectrum of A. testudineus juveniles is very wide; larvae and young fry feed on phytoplankton and zooplankton while large fry (and adults) feed on crustaceans, worms, mollusks, algae, soft higher plants, and organic debris. Adults feed mainly on insects. Reproduction occurs in low lying swamps, paddies, lakes, pools, small pits, ditches, streams, rivers, and irrigation canals. A. testudineus attains sexual maturity in the first year. It is categorized by the International Union for Conservation of Nature and Natural Resources (ICUN) as a vulnerable species. Classification: Kingdom: Animalia Phylum: Chordata Class: Actinopterygii Order: Perciformes Family: Anabantidae Genus: Anabas Species: A. testudineus Scientific name: A. testudineus Common English name: Climbing perch Local name: Koi Fig. 1. External feature of A. testudineus Life history: Adults mating Released eggs Hatched Larva Before Hatching Fig. 2. Life cycle of A. testudineus Morphology: Dorsal spines (total): 16 - 20; Dorsal soft rays (total): 7 - 10; Anal spines: 9 - 11; Analsoft rays: 8 11 Color in life dark to pale greenish, very pale below, back dusky to olive; head with longitudinal stripes ventrally; posterior margin of opercle with a dark spot; iris golden reddish. Body form variable, affected by age and amount of food consumed. Scaled head with 4-5 rows between eye and rear margin of preoperculum. Scales large and regularly arranged, ciliate. Distribution: The species complex is widely distributed in Pakistan, India, Bangladesh, Nepal, Bhutan (most likely), Sri Lanka, Myanmar, Thailand, Cambodia, Laos, Vietnam, southern China, Malaysia, Indonesia,Brunei,Singapore and introduced to the Philippines. Found mostly in canals, lakes, ponds, swamps and estuaries. Adults occur in medium to large rivers, brooks, flooded fields and stagnant water bodies including sluggish flowing canals. Often found in areas with dense vegetation. Can tolerate extremely unfavorable water conditions and is associated mainly with turbid, stagnant waters. They remain buried under the mud during dry season. Food & Feeding habit: Feed on macrophytic vegetation, shrimps and fish fry. Chiefly predatory though wild fish apparently feed on some vegetative matter including algae and rice grains as well as smaller fishes, invertebrates and molluscs. Growth: Better growth performance in Koi, A. testudineus (Bloch) was observed through utilization of poultry viscera in the formulated fish feed, compared to fishmeal. This species grows to 25 cm (9.8 in) in total length. Maturity: First sexual maturity of male and female at 8.0 cm/I 1.3 g and 8.2 cm/12.2 g respectively. Sexual dimorphism: Male and female fishes are identified only during the breeding season, by the difference in their color. During the breeding season, the females show a brilliant orange color with shades of yellow on the ventral side of the abdomen and also on the pelvic fin. During spawning season the abdomen of the female is slightly bulged out. Sexually active females are slightly larger and noticeably thicker-bodied than males, while males are darker in coloration and apparently develop tubercles on the pectoral fins when breeding. Breeding behavior: A. testudineus is bisexual. Sexual dimorphism is generally observed with the approach of the breeding season. Sexual differences of A. testudineus is on the basis of the body and fin colorations. Female 'Koi' shows brown color on the body and fins, particularly the pelvics which turn deep brown during breeding season. This coloration, which indicates the ripening oft he ova, appears during pre-spawning season and gradually disappears after spawning. Mature males acquire glazy black color during breeding season. Color of the mature males as reddish hue on the body, particularly on the pectoral and ventral fins, while females do not show reddish hue. However, color pattern differs considerably in different localities. Fecundity: fecundity is the actual reproductive rate of an organism or population, measured by the number of gametes (eggs). Fecundity is similar to fertility, the natural capability to produce offspring.The fecundity of laboratory reared 'Koi' is reported to be as low as 4,200 to 5,000, with an average of 4,591 and that of pond reared specimens varying between 8,500 and 10,804 with an average of9,935. Embryonic Development: The formation of heart start at 17:00 h ( Fig. a24) followed by beating at 1 h (Fig. a25) later with slow pulsation (33-50 min-1). Blood start to circulate at 19:00 h after fertilization where bloods were pumped every 60-70 heart beats/min) (Fig. a26). Fig.3. Embryonic development in Anabas testudineus, (1) Fertilised eggs, (2) Blastodisc formation, (3) 2 cell, (4) 4 cell, (5) 8 cell, (6) 16 cell, (7) 32 cell, (8) 64 cell, (9) 128 cell, (10) Morula, (11) Early blastula, (12) Middle blastula, (13) Late blastula, (14) Pre-early gastrula, (15) Early gastrula, (16) Pre-mid gastrula, (17) Mid gastrula, (18) Late gastrula, (19) Early neurula (Head formation), (20) Late neurula (optic bud formation), (21) 4 somite, (22) 6 somite (Brain and otic vesicle formation), (23) 9 somite (Appearance of heart anlage), (24) 12 somite (Heart formation), (25) 16 somite (atart of heart beaf), (26) 18-19 somite (onset of blood circulation), (27) Newly hatched larvae, (28) 1st day larvae; 1.8 mm, (29) 2 day old larvae; 2.8 mm, (30) 3 day old larvae; 3.8 mm, (31) 4 day old larvae; 4.3 mm, (32) 5 day old larvae; 4.8 mm and (33) 6 day old larvae; 5 mm Hatching (Newly hatch larvae):Twenty hour after fertilization (Fig. a27), the eggs started to hatch at water temperature of 26-27°C. The newly hatched larva has unpigmented eyes, the mouth not formed but anus situated posterior to the yolk mass. Total length of newly hatched larvae was 0.6 -1 mm. There were 22 pairs of somites. The fish was transparent microscopically with some star or branch-shaped melanophores distributed on both side of the body and the back of the head and somites. Star shaped, dark black-brown melanophores were present on both sides of the yolk sac. The digestive duct were thin and undistinguished, as it was attached tightly to the yolk sac. The mouth and anus was not open and the branchial skeleton still undeveloped. The optic vesicles are not unpigmented. The pigmentation extended uniformly from the head along the trunk, except for the final section of the tail. The larvae body was straight, floating on the water surface. First day old larvae: Total length of first day old larvae (Fig. a28) ranged from 1-1.8 mm. Mouth and anus started to open. Lateral line was visible. Swim bladder and nostril also formed. Majority of larvae still remained motionless in the surface layer of water. The pigmentation extended to the yolk sac both dorsally and ventrally. Typical star-shaped melanophores clusters appear around the final tract of the intestine. Two day old larvae: Total length of two day old larvae ( Fig. a29) ranged from 2.8 mm. Upper and lower jaws were formed. Mouth and anus opened and nostril were also formed. At this point, larvae started to eat rotifer and they were passively carried by water current in the aquarium. Three day old larvae: Total length of three day old larvae (Fig. a30) ranged from 3.8 mm. Eyes became pigmented. Larvae began settling to bottom of the aquarium. They were still carried by water current. Myomeres were observable. Four day old larvae: Total length of four-day-old larvae (Fig. a31) ranged from 4.3 mm. Caudal fin ray started to appeared. Several stellate or punctate melanophores were appeared on upper jaws. Larvae had a transparent pectoral fin fold. Fifth day old larvae: Total length of fifth-day-old larvae (Fig. a32) ranged from 4.8 mm Myomeres began to develop. Caudal fin development proceeded. Dorsal, anal and pectoral fin rays appeared. The mouth was opened and good development of upper jaws and lower jaws, able to take food. Six day old larvae: Total length of six-day-old larvae ( Fig. a33) ranged from 5.0 mm. Dorsal and anal fin ray anlagen appearing. Soft ray caudal also developed. Melanophores appearing in lower jaw and caudal fin. At this point, more larvae were settling to bottom of the aquarium. Larval developmental stages in table: A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. The larvae looked transparent (blood circulation and bonny structure were easily visible) with a straight body. The larval development stages of A. testudineus are given as follows: Time after hatching Length of larvae (mm) Developmental features Oh 2.1 Large oval yolk sac; 21 myotomes; larva darts if disturbed 6h 2.3 Body well pigmented; lens placode appears on unpigmented eye; pectoral fin bud visible 12 h 2.7 Blood still colorless; eye gets pigmented; gill rudiment appears 24h 3.2 Operculum, scale marks and caudal fin rays appear; mouth not yet open 2nd 3.4 Operculum distinct; gill arches and gill filaments appear; well developed open mouth; larva starts feeding; yolk depletion evident; reddish tinge to blood (Hemoglobin synthesis begins) 3rd 3.5 Movable eyes with lens; active feeding and swimming; gut opens out by a striopore; yolk absorbed to a great extent, blood with distinct red color; gill lamellae appear. Conclusion: Thai climbing perch (A. testudineus) is an important fish species in Bangladesh. Due to high growth rate and better return compared to other species, marginal farmers are very much interested to culture it. Furthermore, it is also becoming a highly demanded fish day-by-day due to its high nutritional value, taste, faster growth and having ability to withstand harsh environmental condition. The species is considered as a valuable food fish species and recommended as diet for the sick and as it contains high amount of iron, copper and easily digestible poly-unsaturated fats and many essential amino acids.