Salinity effects on reproduction of giant freshwater prawn Macrobrachium rosenbergii (de Man)

Understanding the role of salinity in breeding and growth has the potential to enhance production of giant freshwater prawn, Macrobrachium rosenbergii. This study investigated the reproduction of females reared in salinities of 0, 6, 12, and 18 g L^− 1. Mean weight of females decreased with increased salinity (31.40 ± 1.54, 25.14 ± 1.16, 20.80 ± 0.81, and 16.62 ± 1.04 g at 0, 6, 12, and 18 g L^− 1, respectively). Larval production was delayed by 2 months in females reared in 12 g L^− 1 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 female. A larval production not only differed between salinity treatments, but also that larval production per gram of female differed between treatments. Females reared in lower salinity of 0 and 6 g L^− 1 produced larger numbers of larvae (12,155 ± 480 and 6519 ± 323, respectively) compared to 12 and 18 g L^− 1 (3751 ± 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). 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 was larger, reproduced early, and produced more offspring than at higher salinity and this could significantly impact coastal prawn culture where seasonal fluctuation of salinity in the hatchery is common.     

Enhancement of Stress Resistance of the Guppy Poecilia reticulata through Feeding with Vitamin C Supplement

This study investigated the use of vitamin C supplement in formulated diets and live Artemia juveniles to enhance the stress resistance of the guppy Poecilia reticulata . To evaluate the stress resistance, fish were subjected to osmotic shock in pre-aerated water containing 35 ppt sodium chloride. Ascorbyl acid-polyphosphate and ascorbyl palmitate were used as vitamin C sources for formulated diets and live Artemia juveniles, respectively. Results showed that guppies fed moist formulated diets supplemented with ascorbic acid at 1,000 mg/kg or 2,000 mg/kg diet displayed significantly higher levels of stress resistance than fish fed control formulated diet for 13 d. The stress resistance of fish fed a lower dose (200 mg/kg diet), however, did not differ significantly from that of the control. On the other hand, the stress resistance of guppies fed Artemia juveniles bio-encapsulated with 10% or 20% ascorbyl palmitate did not show significant difference from that of fish fed control Artemia after 20 d. The stress resistance of these three groups of Artemia- fed fish, however, was significantly higher than that of fish fed the control formulated diet. Biochemical analyses showed that raising the ascorbic acid level in feeds resulted in a concomitant increase in the incorporated ascorbic acid level in the whole-body tissue of the guppy. The increased stress resistance of the guppy fed a vitamin C supplemented diet has also been demonstrated in four commercial farms. The potential application of the improved stress resistance in the ornamental fish industry was discussed.