Maejo International Journal of Science and Technology (Aug 2008)
Embryonic development, hatching, mineral consumption, and survival of Macrobrachium rosenbergii (de Man) reared in artificial seawater in closed recirculating water system at different levels of salinity
Abstract
This experiment aims to study the effect of different levels of salinity (5, 15 and 25 ppt) using artificial sea water on the embryonic development and hatching percentage of the eggs of unripe berried female giant freshwater prawns (Macrobrachium rosenbergii) with an average size of 14.3+0.6 cm TL. After incubation through the heart beating stage (grayish black eggs), the brooders in each salinity were separately transferred to the hatching tank with 15 ppt saline water for the second part of the study. After hatching, the healthy larvae from the brooders which were previously incubated in 3 levels of salinity were collected for the larviculture experiment. The closed recirculating water system with trickling filter unit packed with fiberglass and bioballs was used as incubation and larviculture units. The metamorphosis period and survival rate were examined. The rearing water from each larviculture aquarium was collected for determination of sodium, magnesium, potassium, calcium and chloride ions. The result showed that the percentage of ripe berried females (with heart beating stage embryos) were not significantly different (p>0.05) between 5 and 15 ppt salinity but their values were significantly higher (p0.05) in the survival rate of post larvae and metamorphosis period among the treatments. The first post larvae stage occurred on the 26th day. During 30 days of larviculture, the survival rate of all treatments was 100% until the 19th day, after which it suddenly decreased. When the concentrations of the ions in the rearing water were determined in all treatments, it was found that the concentration of magnesium ions rapidly declined (p0.05). The low survival rate during the final stage of larviculture might be due to the depletion of the previously mentioned ions especially that of magnesium.
