Reproductive Biology Of Bornean Endemic Fish Hampala Bimaculata (Popta, 1905)

Abstract

Hampala bimaculata is an endemic species of Borneo. The fish is very sensitive to poor water quality, reason why inhabit mainly clear rivers or streams with running water with sandy to muddy bottoms. Although, H. bimaculata is a food fish, being also popular in sport fishing, little is known of the important aspects of its reproduction to assist with fisheries management planning. For the first time, this study described and determined the general reproductive biology of H. bimaculata with regards to gonads development, type of ovarian organization, spawning type, sex ratio, size at first maturity, spawning season, and fecundity. This study also estimated population and habitat preference of H. bimaculata based on fish population collected in Betung Kerihun National Park, West Kalimantan Province. A total of 181 individuals specimens were collected from February to October 2013 and the collection continued from July to November 2014 using gill nets and anglings. The fish samples were caught in Embaloh (124’31.6”N-119’18.3”S and 11223’44”-11229’36.8”E) and Sibau (120’33.6”N-102’39.8”S and 11253’23”- 11315’08.1” E) watersheds in the Betung Kerihun National Park, West Kalimantan Province, Indonesia. The total length (TL) of the fish was taken on a fish measuring board to the nearest milimeter. The fish samples were weighed in terms of total weight (W) using digital balance. The fish samples were then dissected, sexed and the gonads were removed and weighed to an accuracy of 0.01 g. Based on macroscopic and microscopic observations, four stages of testicular maturation were distinguished for H. bimaculata i.e. immature or resting, maturing, mature and spent. The ovaries development were classified into five stages: immature or resting, maturing, mature, ripe, and spawned-recovering. Histological analysis of the ovarian development indicated that H. bimaculata exhibits synchronous group, in that at least two groups (cluthches) of oocytes can be distinguished at the same time during the reproductive cycle. The presence of different oocytes development sizes in the spawned and recovering stage and polymodal distribution of oocyte diameter in ripe stage of this fish might indicate a batch spawner. The sample data showed that males’ size ranged from 205 mm to 475 mm in total length and 105 g to 800 g in total weight. Females were 220 mm to 620 mm in total length and 110 g to 3050 g in total weight. The overall sex ratio was 1:2.23 males to females shows significant deviation from the expected 1: 1 (p<0.05). Females seem to be dominant compared with males. Size structure ranged from 200 to 620 mm total length (TL) with significant difference in sex ratio which departed from (1:1) for fish measuring between 350 and 549 mm TL. Meanwhile, estimated L50 values for size at first maturity were 375.7 mm for males and 450.9 mm for females. The length-weight relations showed an allometric negative growth for males (b = 2.73) and isometric for females (b=2.98). H. bimaculata in the waters of Betung Kerihun National Park has a iv prolonged spawning season, being restricted mainly from late July to October, but some spawning may also occur in early November. Fecundity of the fish was relatively high, which the relationships between fecundity and the parameters under study showed the fecundity is significantly correlated to the total length and total body weight. The estimated H. bimaculata population in Sibau watershed was relatively abundant. Based on distribution of each maturity stage at the stations, the potential spawning sites of the fish were in the upper Menjakan river and the upper Apeyang river. The water velocity had positive effects, and while water depth had a negative effect on H. bimaculata based on analysis of linier model. This study also exhibited that H. bimaculata have developed different reproductive strategies on various aspects of reproduction with H. macrolepidota, including size at first maturity, spawning type, spawning season and fecundity. These strategies were carried out as adaptation on environmental factors. .