Fe D. Parado-Estepa

Effect of salinity on the osmotic, chloride, total protein and calcium concentrations in the hemolymph of the prawn Peneaus monodon (fabricius)☆

Abstract 1. 1. Osmolality and chloride concentrations in the hemolymph of Penaeus monodon became stable 1 day after molting in 32 ppt, while total protein and calcium concentrations remained stable throughout the molting cycle. When intermolt (≥ 36 hr postmolt) animals were transferred from control (32 ppt) to experimental (8–40 ppt) salinities, osmolality, chloride and total protein, but not calcium, concentrations in the hemolymph achieved steady state values 24–48 hr after transfer. 2. 2. The hemolymph osmolality was a linear function (slope = 0.28) of medium osmolality at salinities between 8 and 40 ppt. It was isosmotic to seawater at 698 mOsm (10 g prawns) and 752 mOsm (30 g), and was hyperosmotic to the medium below isosmotic concentrations, and hypoosmotic to those above. 3. 3. Hemolymph chloride concentration was isoionic to seawater at 334 mM, and was hyperregulated below isoionic concentrations, and hyporegulated to those above. 4. 4. P. monodon maintained its hemolymph calcium concentration between 6.4 and 10 mM when medium salinities increased from 8 to 40 ppt. 5. 5. Total protein concentration in the hemolymph was independent of medium salinity (8–40 ppt) and hemolymph osmolality (540–850 mOsm).

Responses of intermolt Penaeus indicus to large fluctuations in environmental salinity.

Abstract The osmotic and chloride regulation by 5- to 10-g intermolt Penaeus indicus was investigated by abruptly changing medium salinity from seawater (32 ppt) to test salinities of 8, 20, 32 (control) or 40 ppt. Hemolymph samples were taken at 0, and then at 0.25, 0.5, 1, 2, 5 and 10 days after the change in salinity, and were analyzed for osmolality and chloride concentrations. Tissue water content was also determined. Throughout the study period, daily mortality was low (1.8%), and was the same among control and experimental salinities. Hemolymph osmolality and chloride as well as tissue water content were stable within 0.25 to 0.5 days after the abrupt salinity change, except for tissue water content at 8 ppt which did not reach a steady state for 2 days. Intermolt P. indicus exhibited hyperosmotic or hyperionic regulation in salinities below isosmotic or isoionic salinities, and hypoosmotic or hypoionic regulation in those above. Hemolymph osmolality and chloride were positive linear functions of external osmolality and chloride concentrations (slope=0.24±0.02 and 0.20±0.02, respectively). Isosmotic and isoionic values were 780 mOsm/kg and 330 mM, respectively. Percentage tissue water decreased as a function of external osmolality (−0.0056% kg mOsm −1 ) and hemolymph osmolality (−0.0232% kg mOsm −1 ), indicating that tissue cells were relatively permeable to hemolymph water, and that the hemolymph acted as a barrier to buffer the cells from large fluctuations in external salinity. These results indicate that, like many penaeids, P. indicus is a good osmoregulator suitable for culture in brackishwater ponds where there are large fluctuations in salinity.

Effect of pH and ammonia on survival and growth of the early larval stages of Penaeus monodon Fabricius

Abstract Lethal toxicity tests of ammonia at different pH levels (7, 7.5, 8, and 8.5) and its effect on survival and growth of the early larval stages of Penaeus monodon were determined. An increase in ammonia toxicity when the water pH increased was revealed in 96 h toxicity tests. Estimated LT50 decreased from 101.09 to 25.16 h for protozoea exposed to 8 ppm ammonia, from 115.79 to 11.26 h for mysis exposed to 24 ppm, and from 51.41 to 22.58 h for PL exposed to 52 ppm ammonia with increase in pH levels. The effect of 3 and 6 ppm ammonia levels at pH levels of 7.0, 7.5, 8.0 and 8.5 on the survival and growth of P. monodon larvae and postlarvae was also investigated in a 16-day sublethal toxicity test. Results indicated that ammonia at 3 and 6 ppm affects both survival and growth of shrimp. Survival was decreased by 27% in 3 ppm and by 48% in 6 ppm ammonia, while growth was reduced by 4.4% in 3 ppm and by 6.5% in 6 ppm ammonia. Increasing pH of the rearing water resulted in significantly lower survival in protozoea, mysis, and postlarval stages. No interactive effect of pH and ammonia was detected.

Effect of salinity on hemolymph calcium concentration during the molt cycle of the prawn Penaeus monodon

Prawns (Penaeus monodon) were obtained from ponds in Iloilo, Philippines, in 1984 and 1985 and maintained in salinities from 8 to 44‰. Total hemolymph calcium was largely affected by molt stage and less so by salinity. A sharp, transient increase in hemolymph calcium occurred 3 to 6 h postmolt, followed by an equally rapid decrease from 6 h postmolt to intermolt. This biphasis response was limited to prawns in 8, 20 and 32‰S; in 44‰S, hemolymph calcium remained the same throughout the sampling period. Peak concentrations of total calcium were greater in low (8 and 20‰S) than in high salinities. Salinity had no effect on the duration of molt cycle nor on time of occurrence of molt. Almost half of molting incidents occurred between 18.01 and 0.00 hrs, and one-third between 0.01 and 06.00 hrs.

Transport of Scylla serrata megalopae at various densities and durations

Abstract The optimal conditions for transport of Scylla serrata megalopae were determined. Loading densities of 50, 100 and 150 ind l −1 of hatchery-reared megalopae were studied over a 6-h simulated transport, including shaking. Survival immediately after transport was significantly higher at 50 ind l −1 (99.3±1.6%) (mean± x %) than at 100 (93.0±5.0) and 150 ind l −1 (94.0±3.8%). The same trend was noted 15 h after transport. Another experiment compared survival of megalopae packed at 50 and 100 ind l −1 with simulated transport of various durations (3, 6, and 9 h) at mobile and stationary conditions. Regardless of the duration and condition of transport, survival was again significantly higher at 50 ind l −1 (86.7±2.4%) compared to 100 ind l −1 (79.7±2.1%). Megalopae that were shaken or remained unshaken for 3 or 6 h had similar survival through transport as those shaken for 9 h. Megalopae that remained unshaken for 9 h gave the lowest survival among treatment groups (38.7±0.2%). Due to cannibalistic behavior, stationary transport conditions may have provided the megalopae with a chance to grasp each other. In a third experiment, a batch of megalopae was packed at water temperature levels of 20, 24, and 28°C (ambient) at 50 and 100 ind l −1 for 6 h simulated transport, including shaking. Density and temperature separately influenced survival. Survival was lower at 28°C than 24°C. Although megalopae were less active at 20°C, survival was similar to that at 24°C and 28°C. These results provide useful information for megalopae transport from hatchery to ponds.