Sibling cannibalism in juvenile barramundi, Lates calcarifer (Actinopterygii: Perciformes: Centropomidae), reared under different light conditions

Background. Cannibalism occurs at various ages or sizes depending on fish species and the respective environments. Barramundi, Lates calcarifer(Bloch, 1790),is a popular and valuable species in aquaculture on the Asian and Australian continents. In its culture, cannibalism can cause severe losses during the early stages of development particularly before fish reach a length of about 10 cm. Hence the present study aimed to study the effect of the two photoperiods, constant darkness and continuous light on the rate of sibling cannibalism in barramundi juveniles reared indoors under intensive conditions. Materials and methods. The indoor experimental setup consisted of two separate systems labelled system 1 and 2. Each system consisted of three rectangular rearing tanks each of 60L capacity connected to a mechanical and a biological water-cleaning unit. System 1 was kept under 24 h of light provided by two 36 watt fluorescent tubes. System 2 was kept under 24 h of darkness except for a short period of 6 min during each feeding time. Each rearing tank was randomly stocked with 187 juveniles. A commercial fish feed was provided to the fish by handad libitum four times during the day time. The experiment was conducted for 112 days. Results. In both light and dark systems, larger specimens were much more active during feeding, chasing smaller siblings away from the provided feed, leaving them only the remains to feed on. The accumulated observed mortality was similar under both dark and light conditions. In the present study although feed was provided ad libitum, cannibalism still occurred under both light and dark conditions. However, the rate of cannibalism was significantly (P < 0.05) lower under dark conditions. The results show that a potential predator can swallow a prey up to a maximum of 67% of its own body length. Similar growth performances were observed in the fish groups reared under darkand lightconditions. Conclusion. The application of constant darkness is therefore a useful strategy in significantly reducing cannibalism when rearing barramundi. Furthermore, such a strategy also leads to the formation of a more uniform population of fish which is a desire of the grower

Effects of Probiotics and Spirulina on Survival and Growth of Juvenile Common Carp (Cyprinus carpio)

A 45-day feeding trial was conducted to investigate the effects of probiotics and spirulina on sur- vival, growth, feed conversion ratio (FCR), protein efficiency ratio (PER), and total heterotroph- ic microbial count in common carp (Cyprinus carpio). Two probiotic organisms (the bacteria Lactobacillus acidophilus and the yeast Saccharomyces cerevisiae) and a single cell protein (Spirulina maximus) were incorporated into diets at concentrations of 1%, 2%, or 3%. The con- trol diet contained no supplement. Spirulina maximus at 3% produced the best and statistically significant (p<0.05) survival, growth (3.69±0.10 g), specific growth rate (1.27±0.02%/d), FCR (0.71±0.08), and PER (1.96±0.03). In general, L. acidophilus produced better growth than S. cerevisiae. The highest FCR (1.93±0.05) was obtained in the control. The total heterotrophic microbial count was highest in S. cerevisiae treatments, followed by L. acidophilus and S. max- imus. The present investigation shows that incorporation of a probiotic or spirulina in diets for common carp results in increased growth rate

Breeding Behaviour and Embryonic Development of Koi Carp (Cyprinus carpio)

Induced breeding experiments of Nikishigoi (koi carp), Cyprinus carpio were conducted in mature males and females by administrating a single intramuscular injection of ovaprim at a dosage of 0.3 mL/kg weight. Spawning was observed six hrs after the injection at ambient temperature (26-28oC). The fertilized eggs were adhesive and transparent with diameter ranging between 0.9 mm and 1.10 mm. Incubation period was 73.00hrs. The hatchlings were transparent and measured 2.7-2.9 mm, with a large oval head, a well defined yolk sac and short tail. The yolk got fully absorbed within 3 days and by this time mouth formation was complete and the larvae started exogenous feeding. After 20 days the length of fry ranged between 10 mm and 12 mm and after 35 days length of the fingerlings ranged from 30-35 mm and appeared just like an adult in all respects except sexual maturity