EFFECT OF TEMPERATURE ON DEVELOPMENT AND SURVIVAL OF TODARODES PACIFICUS EMBRYOS AND PARALARVAE

Embryonic development and survival of paralarvae of the Japanese commo n squid Todarodes pacificus (Steenstrup, 1880), were examined at 16 te mperatures (3-39 degrees C) to determine the optimum temperature range for development and survival. Normal embryonic development occurred a t temperatures between 14.0 degrees and 26.0 degrees C, with highest e mbryonic survival rates occurring between 14.7 degrees and 22.2 degree s C. The relationship between temperature (T) and the number of days f rom artificial fertilization to hatching (D) is expressed by a polynom ial function: ln(D) = 4.73 - 0.227(T) + 0.00304(T-2). A modified formu la, based on observations of two egg masses spawned in captivity, was used to estimate the development rate of eggs within naturally spawned egg masses. It is suggested that T. pacificus spawns in waters wanner than 12.1 degrees C, and egg masses maintain their structure for 4.0 - 9.5 days before disintegrating at temperatures between 14.7 degrees and 22.2 degrees C. Paralarvae survived up to 13 days after hatching, with the highest survival rates occurring at 15 degrees C.