Ambok Bolong Abol-Munafi

Effect of hydrogen ion on Macrobrachium rosenbergii (de Man) egg hatchability in brackish water

Abstract The effect of hydrogen ion on egg hatchability of Macrobrachium rosenbergii (de Man) in brackish water was studied. A bioassay using the artificial hatching of fertilized M. rosenbergii eggs in flow-through system was employed in this study . The experimental conditions were set at salinity 12 g/l, temperature 30 °C, DO >5 mg/l, unionized ammonia The results indicated that M. rosenbergii egg hatchability is extremely sensitive to hydrogen ion concentration in brackish water. In brackish water of 12 g/l salinity, the highest hatching rate was detected at pH 7.0 with value of 92.22±1.72%. At pH 6.5 and 7.5, hatching rates drastically dropped to 5.00±3.50% and 13.33±2.98%, respectively. While at pH of 5.0, 8.0, 9.0 and 10.0, the hatching rates were zero. This study implies that pH of the brackish water for M. rosenbergii hatchery operation should be maintained at 7. This will increase the hatching success of the prawns and reduce the number of brood stock required for the hatchery operation.

Thermal tolerance and locomotor activity of blue swimmer crab Portunus pelagicus instar reared at different temperatures

Owing to its potential market value, the blue swimmer crab Portunus pelagicus is of great economic importance. The temperature of water significantly affects the physiological function and production efficiency of these crabs. The aim of the present study was therefore to examine the critical thermal minimum (CTMin), critical thermal maximum (CTMax), acclimation response ratio (ARR), escaping temperature (Tesc), and locomotor behavior of P. pelagicus instars at 20 °C, 24 °C, 28 °C, 32 °C, and 36 °C. The CTMax ranged from 39.05 °C to 44.38 °C, while the CTMin ranged from 13.05 °C to 19.30 °C, and both increased directly with temperature. The ARR ranged from 0.25 to 0.51. The movement of crabs (walking before molting) correlated positively with the acclimation temperature. These results indicate that the parameters evaluated varied with temperature. Furthermore, the high CTMax indicates the potential of this species to adapt to a wide range of temperatures. In addition, the implications of these findings for portunid crabs behavior and distribution in their natural habitat are also discussed.

Effect of different diets on growth and survival rates of snakehead (channa striata bloch, 1797) larvae

A study was conducted to determine growth and survival rates of snakehead (Channa striata) larvae. Live foods such as Artemia salina naupiii, Moina micrura and bloodworm and artificial diet were given to larvae from 1–15 days after hatching as the 1st phase and from 15–30 days as the 2nd phase. In the 1st phase, the growth and survival rates of larvae fed with Artemia nauplii were significantly different from larvae fed with Moina (p<0.05) with values of 28.5 mg, 49% and 26.7 mg, 31%, respectively. Meanwhile, all larvae fed with bloodworm (Chironomus sp.) or artificial diet (49% protein) died within 10 days of experiment. For the 2nd phase, growth of the fry fed with Artemia or Moina differed significantly from that fed with bloodworm or pellet (200.1, 187.7, 109.6 and 8.2 mg, respectively). Specific growth rate (SGR) of larvae fed with Moina was higher than that of larvae fed with Artemia (17.9 and 17.4% day‐1 respectively) in the 1st phase. In the 2nd phase, SGRs of larvae fed with Artemia (12.7% day‐1) or Moina (11.5% day‐1) were significantly higher than those of larvae fed with bloodworm (8.3% day‐1) or dry diet (6.1% day‐1). Generally, Artemia and Moina were suitable food for snakehead larvae during the first month of their life, and artificial diet was much less acceptable and resulted in poor growth and survival.

The hormone 17β-estradiol promotes feminization of juveniles protandrous hermaphrodite false clownfish (Amphiprion ocellaris)

Abstract The social structure of the false clownfish (Amphiprion ocellaris) typically consists of a pair of functional brooders within a population of individuals which remain as protandrous hermaphrodites usually incapable of breeding. This situation often hampers the commercial scale production of large numbers of clownfish offspring and broodstock. To enhance breeding outputs, protandrous hermaphrodites must be converted to functional brooders with a distinct sex prior to pairing and breeding. In this study, 17β-estradiol (E2) was used to feminize juveniles of A. ocellaris, with groups of fish incubated at 0.1, 0.2, and 0.4 mgL−1 E2 for 15 days. The gender was substantiated on the basis of gonad histological profiles after 15, 30, and 60 days, work that includes verification of the safety levels of this hormone used in this application. All the treatments employed induced feminization, as shown by histology profiles revealing degenerate male germ cells and testes tissues and several developed ovarian cells at different stages (oogonia, previtellogenic and vitellogenic) 30 days after E2 incubation. Conversely, gonad profiles of non-treated fish did not change. The gonads possessed both ovarian and testicular tissues, a typical characteristic indicating that the fish are still ambisexual. Although E2 was effective in promoting gonad maturation, incubation of fish in high concentrations adversely affected fish survival. Mortalities occurred when E2 exceeded 0.1 mgL−1. The latter concentration is considered the most appropriate level for inducing feminization and at the same time, maintaining the well-being of the organism.