A Study of Embryonic, Larval and Postlarval Responses to Conditions of Water Hardness and Alkalinity in Macrobrachium rosenbergii (De Man) 1879.

Abstract

Macrobrachium rosenbergii (De Man) has been transferred to several sites around the world for its potential of culture and commercialisation, however, some countries like Mexico, have limitations regarding the levels of calcium carbonate in its waters. Up to now there is some controversy in the results of the effect of calcium carbonate on the development in the species, therefore, the responses of embryonic, larval and postlarval M. rosenbergii to different environmental conditions of water hardness and alkalinity were investigated. This study was made in two separate stages, the first investigated the effects of alkalinity and total hardness as two separate factors affecting the performance of postlarvae, and the second investigated the possibility of adjusting the tolerance limits of the species to alkalinity, the most important of the two environmental variables. Alkalinity reduced the growth rate and survival of postlarvae of M. rosenbergii, and at the same time increased their moult frequency. Besides, it was found that an alkalinity concentration of 250 mg L'1 (as CaCC>3) or above was lethal for postlarvae of the species. Total hardness as high as 1000 mg L'1 (as CaCC>3) however, did not have any significant effect in the growth rate or survival as long as the alkalinity was 100 mg L'1 (as CaCC>3) or lower. Acclimatisation of the embryos of M. rosenbergii to alkalinity levels as high as 200 (mg L_1 as CaCCh) did not reduce in a significant way the effect of high alkalinity in the postlarval stages of the species.