Abstract
This thesis examines the stock variability of bele (Glossogobius giuris) of pond, haor and estuary and establishing its induced breeding technique using best selected stocks. Six experiments were conducted under the Department of Fisheries Biology and Genetics, Faculty of Fisheries, Bangladesh Agricultural University, Mymensingh, Bangladesh. To identify the desired stock samples of bele (G. giuris) were collected from three different stocks such as pond of Mymensingh, haor of Mithamoin, Kishoreganj and estuary of Barisal. Twelve general morphometric, 23 landmark-based morphometric measurements and 11 meristic characters were studied. Among the 11 meristic counts the first dorsal fin rays (D1FR), transverse scale above lateral line (TSALL), branchiostegal rays and number of vertebrae were same among fishes from these stocks. In case of pectoral fin rays (PcFR) and transverse scale on lateral line (TSOLL) the haor stock of Kishoreganj was significantly higher than other stocks. All 12 size adjusted general morphometric and 23 size adjusted landmark-based measurements were significantly different (P<0.01) from each other. This resulted that pond stock was morphologically dissimilar to other two stocks possibly because of confinement and other environmental conditions. The haor and estuary stocks showed very close relationship may be due to their natural habitats. Most of the morphometric and meristic characteristics of the haor stock performed better than the estuarine stock. To find out the breeding season of the bele (G. giuris) samples were collected for 12 consecutive months from the haor of Kishoreganj. Ovarian development and maturation stages of germ cells were examined. Values of gonado-somatic index (GSI) ranged from 0.86±0.37 to 4.69±0.13 in female and 0.28±0.07 to 1.48±0.31 in male fish. Higher values of GSI were observed during July to September which ranged from 4.01±0.29 to 4.69±0.13 in female and 1.20±0.19 to 1.48±0.31 in male during June to August. The fecundity was found to vary from 2,18,965 to 3,67,324 indicating the fish as highly fecund. Histological study of ovarian and testicular development of bele (G. giuris) indicated that the fish breed during May to September in the natural habitat. During the domestication in controlled environment the fish were fed with clean and chopped chicken viscera (T1), trash fish (T2) and formulated feed (T3) at the rate of 3% body weight day-1. Each treatment had three replications and stocked with 50 fish/2 decimal ponds (initial weight 40.35±1.35g). The protein percentages of feeds were 47.58, 55.20 and 43.50 in T1, T2 and T3, respectively. The significantly (P<0.05) higher growth were observed in T2 (288.10±4.18g) and T1 (287.90±4.38g) compared to T3 (153.1±4.86g) but there was no significant difference in growth between the T2 and T1. The SGRS were 0.24+.004 0.24+.003 and 0.161.003% day-1 and survival rates were 90, 89 and 77% in T1, T2 and T3, respectively. In both cases significantly lower (P<0.05) growth were observed in T3 than the other two treatments. It was found that the fish easily became accustomed with chicken viscera and trash fish as feed as the fish is carnivorous in nature. Upon successful domestication of bele (G. giuris) in control environment an attempt was made to establish induced breeding technique and studying the embryonic and larval developmental stages. First breeding trial was conducted in June using 40, 45, and 50 mg PGkg1 body weight of the female fish. None of the fish ovulated in 1st trial. Two more breeding trials were conducted in July and August using 6 mg (T1), 8 mg (T2) and 10 mg (T3) PG kg1 body weight of female fish and 3 mg (T1), 4 mg (T2) and 5 mg (T3) PG kg 1 body weight of male fish. The single dose of 4 mg kg-1 body weight of PG was found to be effective for male fish in both months. The ovulation rates were recorded as 56.33±1.53, 82.67±2.52 and 75.33±1.53% in July and 58±2.65, 94.67±1.53 and 78.33±1.53% in August under the T1, T2 and T3, respectively. Hatching rates of eggs were observed as 52.00±4.36, 81.67±3.21 and 72.33±6.03% in July; 54.67±3.23, 91.67±3.06 and 73.67±5.13% in August under the T1, T2 and T3, respectively. Hatching time ranged from 35-48 h and after absorption of yolk sac (60-72 h) they survived well when fed with tubificid worms and mixed zooplankton. The female treated with the dose of 8 mg PG kg-1 body weight in August showed the best performance so far as the ovulation, fertilization and hatching rates are concerned. The successive embryonic and larval developmental stages were investigated and described in details.