Abstract
The effects of temperature and salinity on the metamorphosis of nauplii into protozoea I of a planktonic shrimp Acetes intermedius were studied. Eggs or nauplii I, hatched under optimal conditions (30°C, 30 ppt), were incubated under 15 different combinations of three temperatures (20°C, 25°C, and 30°C) and five salinities (15 ppt, 20 ppt, 25 ppt, 30 ppt, and 35 ppt) until reaching protozoea I stage. At salinities of 20-35 ppt, eggs required 28 h, 45 h and nearly 4-5 days to develop into protozoea I at 30°C, 25°C and 20°C, respectively. Nauplii metamorphosed into protozoea I at salinities of 25 ppt and 30 ppt earlier than at 20 ppt and 35 ppt at temperatures of 25°C and 30°C, whereas no regularity in time length existed among salinities at 20°C. Irrespective of hatching conditions, the rate of metamorphosis reached approximately 90-100% at temperatures of 25°C and 30°C at salinities of 20-30 ppt, but was significantly reduced at 20°C for all salinities examined. The metamorphosis rate of nauplii was generally higher at salinities of 20-30 ppt at all temperatures. Multiple linear regression analysis revealed that the temperature experienced by nauplii accounted for most of the variation in the metamorphosis rate.
