The effects of varying sampling intervals on the growth and survival of Heterobranchus longifilis (Valenciennes, 1840) fry in outdoor nursery management
Four different sampling intervals were investigated during a six-week outdoor nursery management of Heterobranchus longifilis (Valenciennes, 1840) fry in outdoor concrete tanks in order to determine the most suitable sampling regime for maximum productivity in terms of optimum growth and survival of hatchlings and minimum development of jumpers (excessive fast growers). The sampling intervals were-weekly, biweekly, triweekly and no sampling until at harvest. The highest percentage survival (72.0%) was recorded where the fish were sampled biweekly while the lowest survival (17.1 %) was recorded in the treatment where fish was not sampled until at harvest. Similarly, the total biomass of fish at the various sampling intervals was greatest (1,471.6g) where the fish was sampled biweekly. The percentage number of jumpers at harvest was highest (13.3%) in the tanks that were not sampled until at harvest while the lowest percentage of jumpers (3.4%) was recorded in the tanks sampled weekly. For the best productivity in terms of survival and total biomass of fish at harvest, sampling of outdoor nursery tanks biweekly is recommended as the best sampling regime for the outdoor nursery management of Heterobranchus longifilis hatchlings.
Key Words: Sampling interval, Heterobranchus longifilis, fry, catfish, outdoor nursery management.