Observations on the hypophysation of murrels (Ophicephalidae)

The four common Indian species of murrels, viz., Ophicephalus striatus (Bloch), Ophicephalus marulius (Hamilton), Ophicephalus gachua (Hamilton) and Ophicephalus punctatus (Bloch) were hypophysed, the former three for the first time.The characters by which sexes in murrels can be distinguished, basis of selection of breeders, hormone doses administered and response, percentage of fertilization of eggs, techniques adopted for hatching of eggs and rearing of larvae and the total developing eggs and spawn produced are reported and discussed.     

Ontogenesis and embryogenesis of Megaleporinus elongatus larvae (Characiformes: Anostomidae) from the Jequitinhonha River Basin

Five females and five males of Megaleporinus elongatus captured in the Jequitinhonha River were transferred to hypophysation tanks with a constant water flow at 26°C at the Machado Mineiro Fish Farm. They were submitted to induced reproduction by the hypophysation method. Crude carp pituitary extract (Cyprinus carpio) was injected into the coelomic cavity in two doses (2.5 and 5.0 mg/kg) for males and 3 doses (2.5, 5.0, and 2.5 mg/kg) for females. The doses were applied with a 24‐hr interval between the 1st and 2nd doses and a 12‐hr interval between the 2nd and 3rd ones. Oocytes and semen were obtained by manual extrusion, and the dry method was used for fertilisation. The eggs were kept in funnel type 20‐litre incubators with constant water flow at 23°C. Egg samples were collected every 10 min and photographed under a stereomicroscope for analysis of embryonic development until hatching. The main events of embryogenesis and their respective duration times were: cleavage (45 min), blastula (3 hr 14 min), gastrula (5 hr 25 min), closure of blastopore (6 hr 34 min), differentiation of somites (13 hr 20 min), tail release (17 hr 50 min), and hatching (24 hr 50 min). During the larval ontogenesis, the yolk sac gradually decreased until its complete reabsorption on the 7th day after hatching. The opening of the mouth and digestive tract occurred from the 5th to the 7th day, indicating that larvae could feed exogenously. These results provide information to improve the techniques of induced spawning and cultivation of M. elongatus.     

Analysis of production,early growth and survival ofClarias gariepinus (Burchell),Heterobranchus longifilis (Val.) (Pisces: Clariidae) and their F1 hybrids in ponds

Clarias gariepinus andHeterobranchus longifilis were successfully hybridized to produce reciprocal F₁ progeny during a two-year study.C. gariepinus produced significantly heavier spawn thanH. longifilis during the same period. Fertilized eggs were incubated in aerated static-water in fibre-glass troughs, and hatching rates were not found to be significantly different (P<0.05) between any two of the four catfish groups produced. Eight-day old fry of each group were reared in fertilized nursery ponds, and F₁ hybrids fromH. longifilis maternal parent had the best growth and survival rates at the end of 18 days. The reciprocal cross showed intermediate growth rate between both parents. At harvest, differential growth was less pronounced among both hybrids than among the parents.