| Abstract | The giant freshwater prawn, Macrobrachium rosenbergii (de Man) has become one of the main species for inland aquaculture in many countries with a global production of over 200,000 tons valued at US$ 893 million (F AO, 2007). Although the larval cycle was closed 50 years ago, scarcity of quality seed remains a major constraint impeding expansion of prawn culture. Better understanding of the environment in which broods can reproduce and larvae can survive and grow well is prerequisite to improving supply of quality seeds. In this study a series of experiments were carried out to understand: a) the relationship between salinity of brine water and associated survival of larvae, b) survival variation of larvae from different sources of broodstocks, c) the influence of different salinity levels on the reproductive performance of broodstock and survival of their larvae, and d) survival and growth of larvae from different male morphotypes. A study on the effects of brine water (collected from different salt processing stages) of different salinities (35, 160, 180, 250, and 310 g L⁻¹) and diluted to 12 g L⁻¹ resulted in varied larval survival. High survival (31.5%) was obtained from brine water diluted from 180 g L⁻¹. The results of laboratory analysis showed that ionic concentrations of brine water vary from low to high salinity. Potassium, sodium, magnesium, chloride, bicarbonate, and sulfate concentrations were positively correlated to salinity except calcium concentration. Larval development at 12 g L⁻¹ from the source of the brine water 180 g L⁻¹ grow faster than those of other sources (35, 160,250, and 310 g L⁻¹). A comparison of larval growth and survival from three sources of broodstocks (hatchery, CPF, and river) revealed that larval survival from hatchery stock (43.62%) was higher than CPF and river stocks (29.15 and 23.08%, respectively). Larvae from wild stock required longer to complete stages of development. First postlarvae appeared in farm hatchery and CPF stocks two days earlier than river stock. This finding highlights the importance of using domesticated stock for production. Influence of different salinity levels (0, 6, 12 and 18 g L⁻¹) on the reproductive performance of broodstock of M rosenbergii was investigated for a period of 17 months in the hatchery condition. Females reared in lower salinity of 0 and 6 g L⁻¹ produced larger number of larvae (12,155±480 and 6,519±323, respectively) compared to higher salinity (12 and 18 g L⁻¹; 3,751±256 and 0, respectively). The number of larvae produced per gram of female was inversely related to the salinity levels (Y= -37.54X + 685.65, n=339, r²=0.995, p<0.05). Production of larvae decreased with seasonally lower temperatures. Egg production was delayed by two months in females reared in 12 g L⁻¹ salinity compared to 6 and 0 g L⁻¹ and the cumulative number of berried females decreased with increased salinity. The number of larvae produced was positively correlated to weight of females. Mean weight of females also decreased with increased salinity. Survival of larvae from females reared at 0 and 6 g L⁻¹ was higher than those from females reared in 12 g L⁻¹. This study clearly shows that female broodstock reared in lower salinity produced earlier and had more offspring than at higher salinities and this could significantly impact coastal prawn culture where seasonal fluctuations of salinity in the hatchery are common. In mature male populations, two distinct male morphotypes (blue claw and small males) are found. Both male morphotypes have the opportunity to fertilize receptive females. A preliminary trial of the larval survival from small males and blue claw males reared at 0, 6, and 12 g L⁻¹ were conducted. No differences were detected between larvae from blue claw and small males reared at different salinities. Among different salinity levels, larval survival from both blue claw and small males at 0 and 6 g L⁻¹ were higher (33.03, 34.47; 38.00, 32.83% respectively) than those from males at 12 g L⁻¹ (15.33, 13.27%). The results suggest that the variation of larval survival is affected more by environmental salinity than the distinct male morphotypes. |