The research was carried out in the Pond Complex and Mini Hatchery of the Department of Fish Biology and Genetics, Sylhet Agricultural University, Sylhet. The hapa breeding technology of C. striatus was set out in earthen pond by using rectangular drag net as a breeding hapa. The research work was done during from January to May 2016. The major approaches and methodologies of the research work are as follows:
2.1 Captive Broodstock of C. striatus Brood fish candidates of C. striatus were collected from wild sources of haor region (latitude 24°34´N to 25°12´N and longitude 90°56´E to 91°49´E) in Sylhet. These fishes were transported in open mouth plastic drum. The weight ranging of brood fish candidates was 600-900g and the fishes were healthy, good looking, disease free. The fishes were transported to the pond complex and stocked in a pond for broodstock development after salt (NaCl) water bathing for prevention of disease.
2.2 Rearing of Brood fish The broodstock pond size was 49 m2 and water height was 1.5 m. A fencing was provided by synthetic net inside the lower part of the pond embankment to protect fish escaping tendency. The natural environment was created in the pond with phytoplankton, zooplankton, insects’ larvae, tadpole and some aquatic macrophytes like Eichhornia crassipes and Hydrilla verticillata etc. Besides, some small live fishes such as mola (Amblypharyngodon mola), punti (Puntius ticto), darkina (Esomus danricus) and tilapia fries (Tilapia mossambicus) were released regularly in the pond as they fed them due to carnivorous nature.
2.3 Breeding Hapa Setting The rectangular iron frame with covering synthetic net was used for hapa making. The breeding hapa was setting in the pond. The size of the breeding hapa was 2 m length, 2 m width and 1.5 m height. Iron frame was used for hapa making and bamboo poles were used for setting hapa in the pond. The base of the breeding hapa was fully submerged at the pond bottom using bricks. Fish shelter and natural environment was created in the breeding hapa through introduction of aquatic macrophytes like Eichhornia crassipes and Hydrilla verticillata. The monitoring and observation facilities of breeding hapa were provided in the pond through extra arrangement of staircase.
2.4 Brood Fish Selection for Breeding The ripe and healthy male and female brood fish were selected based on physical and visual examination of secondary sexual characteristics i.e., size, color, swollen abdomen and genital opening. Cast net and seine net were used to collect brood fish whenever necessary by reducing the water of the pond. The brood fishes were selected carefully from captive broodstock hope to get positive response for breeding. Male brood fish were selected on the inflamed body surface. On the other hand, female brood fishes were selected by observation rounded, swollen belly, and reddish protruded genital opening. The selected brood fishes were kept into the cistern of Mini Hatchery for acclimatization and resting for inducing injection. After 4 h of resting period, finally six breeding sets of brood fishes, two (2) males and one (1) female in each breeding set, ranging between 650 g and 860 g were selected for inducing injection.
2.5 Experimental design Three treatments were designed and considered as T1, T2 and T3 (control). Pituitary gland hormone was used as inducing agent in treatment-1 (T1) where ovupin (compound S-GnRHa) was used in treatment-2 (T2) and no inducing agent was used in treatment-3 (T3, control). Each treatment consists two breeding sets. Two males and one female of brood fish were used in a breeding hapa. The hormones were applied at two different doses. The primer dose for female was 2.0 mg/kg and 0.5 ml/kg of PG and Ovupin, respectively. The second dose for female was 6.0 mg/kg and 1.0 ml/kg of PG and Ovupin after the interval of 6 h. The male only received the second dose of hormones at the rate of primer dose of female.
2.6 Inducing of Brood Fish and Kept in the Breeding Hapa The selected brood fishes were injected by using inducing agents at the Mini Hatchery of the Department of Fish Biology & Genetics. The inducing agent was used as per the experimental design. Then the injected female and male fishes were stocked together in the breeding hapa.
2.7 Feeding and health care of Brood fish The live small fishes like mola and darkina were supplied into the breeding hapa as feed of C. stratus. Water hyacinth was added into the breeding hapa to create natural environment in the hapa as well as to control jumping of fish for avoiding injuries.
2.8 Breeding and spawning situation The brood fishes in the breeding hapa were monitored and observed minutely. Fish breeding, spawning time, fertilization rate, hatching rate were observed closely and necessary work was done carefully. The following formula was used for fertilization and hatching rate:
2.9 Measurement of water quality The water quality parameters of the breeding hapa were recorded carefully. Water quality parameters such as temperature, pH and dissolved oxygen (DO) were measured daily. Digital pH meter (Lutron, Model- PH-222) was used for the measurement of pH, a DO meter (Lutron DO-5509) was used for the measurement of DO and a thermometer was used for recording of water temperature. 2.10 Data analysis Data were analyzed by using the statistical package IBM SPSS version 22.