EXPERIMENTAL STUDY ON THE SALINITY TOLERANCE OF FRESH WATER PRAWN Macrobrachium rude (HELLER, 1862) LARVAE
Mariculture has rapidly expanded over the last two decades due to new technology, improvements in formulated feeds, greater biological understanding of farmed species, increased water quality within closed farm systems, greater demand for seafood products, site expansion and government interest. Early developmental stages of prawns are very critical due to vulnerability of the organism to environmental conditions such as salinity. Previous studies have been done on Fresh water prawn. Some of the researched fields include: Macrobrachium species, Androgenic gland ablation, Polyculture and Disease of Fresh Water prawn, Macrobrachium rosenbergii . The main aim of this study was to examine if difference in salinity affects survival and growth of prawns, it narrowed down to determining if difference in salinity levels influences hatching of mature eggs in prawn adult and if difference in salinity levels affects survival and development of early larval stages of prawns.Mature berried adults were collected and observed as natural spawning and hatching of eggs was observed in the laboratory in basins with water at different salinity levels; 0ppt, 7ppt, 10ppt, 12ppt and 14ppt. The nauplii were collected and placed in beakers holding water at different salinities; 0ppt, 7ppt, 14ppt, 21ppt, 28ppt and 35ppt. each with three replicates. The survival rate was determined from nauplii stage to Mysis stage through zoea stage up to day seven. The temperature as an extraneous variable was maintained constant at room temperature of 270c. This study revealed that berried females appear to prefer a medium salinity of 14‰ for spawning and hatching their eggs. Close similar findings were reported for M. rosenbergii whose larvae and adults are 'euryhaline to a considerable degree. From the study, fresh water prawn can be classified as euryhaline. It shows a preference for lower salinities (7‰- 21‰) for spawning, as well as for the survival, growth and development of its larvae.
The best salinity ranges for survival of prawn larvae is 7±3.7 ppt minimum and 14±10 ppt maximum
Thus; 92.7% variability in the model is caused by salinity whereas 7.3% variability in the model is caused by other factors e.g. Ph.