Browsing by Author "Gonzal, Angelito C."
Effect of stunting of juvenile bighead carp Aristichthys nobilis (Richardson) on compensatory growth and reproduction The study was conducted to determine if stunting of young bighead carp Aristichtys nobilis (Richardson) would affect subsequent growth and reproduction. Juveniles (3 g each) were stocked directly in cages (control) in a lake or stunted in tanks for 6, 12, 18 or 24 months before being stocked in cages. Initially, body weights and lengths of stunted carp in cages were significantly lower (P<0.05) than those of the control fish. The carp stunted for 6, 12 and 18 months showed growth compensation, although their weights and lengths were slightly lower than those of the control fish. The body weight and length of fish stunted for 24 months were the lowest throughout the rearing period. Sexual maturation occurred only in the control fish and those stunted for 6 and 12 months. However, the onset of gonad maturity was delayed significantly (P<0.05) in males stunted for 12 months and in both groups of stunted female fish. The relative fecundity (44 000–56 000 eggs per kg body weight) and number of 3-day-old larvae produced per female (78 000–89 000) did not differ significantly among the three treatments (P>0.05), but production was somewhat lower in fish stunted for 12 months.
The effects of water hardness on the hatching and viability of silver carp (Hypophthalmichthys molitrix) eggs An investigation was conducted to establish water hardness concentration for optimum hatching of silver carp (Hypophthalmichthys molitrix) eggs. Eggs were incubated for 19 h at 26.5°C at six levels of water hardness: 100, 200, 300, 400, 500 and 600 mg/l CaCO3. Water absorption at 100–200 mg/l CaCO3 caused eggs to burst prematurely and minimal water absorption occurred at 600 mg/l CaCO3. Chloride concentration at 0 and 6 h post-fertilization was significantly related to egg hatchability. Total ammonia-nitrogen at 6 h, pH at 6 h, magnesium hardness at 18 h and chlorides at 18 h significantly influence viability of larvae. A water hardness of 300–500 mg/l CaCO3 is recommended for the successful hatching of silver carp eggs.