The effects of a marine photosynthetic bacteria Rhodovulum sulfidophilum on the growth and survival rate of Marsupenaeus japonicus (kuruma shrimp)

The sustainability of the shrimp aquaculture depends largely on disease control and the health status of shrimp. Probiotics, which make shrimps healthier and more resistant to pathogens, are promising countermeasure for shrimp diseases. In this study, the effects of the marine purple non-sulfur photosynthetic bacterium (PNSB) Rhodovulum sulfidophilum on Marsupenaeus japonicus (kuruma shrimp) growth and survival were examined in 177 m2 aquaria (140 tons of water) for 70 days. The shrimp received feed containing 0.01 % fresh weight (106 colony forming unit/g) of R. sulfidophilum cells. The survival rate significantly improved (P < 0.001) (R. sulfidophilum-fed = 81.9 %; control = 71.5 %), the feed conversion rate improved (R. sulfidophilum-fed = 1.83; control = 2.11), and there was no difference in the shrimp average body weight. The approximate bacterial cell cost was $0.003 to $0.005 per 1 kg feed, indicating that the R. sulfidophilum approach is economically feasible and a promising candidate for probiotic bacteria in shrimp aquaculture. Keywords: photosynthetic bacteria, Rhodovulum sulfidophilum, Marsupenaeus japonicus, shrimp, probiotics

Grading frequency affect the growth performance and intra−cohort cannibalism in African catfish (Clarias gariepinus, burchell, 1822) culture

Growth of African catfish (Clarias garipinus) is characterized by large size heterogeneity resulting in poor growth performance and cannibalism. Strategies that limit size heterogeneity in C. gariepinus culture are therefore advocated. This study determined the effects of grading frequency on the growth performance and cannibalism of C. gariepinus in tank culture system. Three treatments designated as G0 (no grading), G2 (grading every 2 weeks) and G4 (grading every four weeks) in a Completely Randomized Design (CRD) was applied in triplicate. The tanks were stocked with 200 fingerlings each. Sampling was conducted weekly to measure length and weight of fish. Mortalities were recorded and dead fish observed under dissecting microscope to ascertain that it is due to cannibalism. Growth performance in terms of final mean weight, weight gain, specific growth rate and food conversion ratio were significantly (P < 0.05) affected by frequency of fish grading. The C. gariepinus graded every two weeks grew better than those graded every four weeks and were all above the no grading treatment. Significant changes in fish heterogeneity were observed after day 42. The size variation was significantly affected by grading frequency. The mean TL of fish graded every 2 weeks was the highest, followed by grading every four weeks and finally the no grading treatment was the lowest. Fish size heterogeneity (CV% and skewness) was consistently the highest in C. gariepinus in no grading treatment followed by fish where grading was done every four weeks while it was lowest in treatment where feeding was done every two weeks. Mortality owing to cannibalism was affected by grading frequency where highest cannibalism mortality occurred in C. gariepinus where there was no grading followed by grading every four weeks and intermediate at grading frequency every four weeks. Meanwhile other mortality by other causes such as such as wounds and suffocation in fish did not differ with grading frequency. Keywords: Cannibalism, Coefficient of variation, Fish grading, Fish growth, Growth heterogeneity