TEMPERATURE EFFECTS ON THE DEVELOPMENTAL RATE OF SQUID (LOLIGO PEALEI) EMBRYOS

¹ Marine Biological Laboratory, Woods Hole, Massachusetts 02543

1. Loligo pealei embryos were readily maintained in flowing sea water between 12.0 and 23.0° C. They were observed and staged according to Arnold's (1965) description of normal embryonic development. Developmental stage vs. time plots fell into three groups with sea water temperature ranges of 12.0-18.0° C, 15.5-21.3° C and 21.5-23.0° C and mean total developmental times of 642, 445 and 257 hr, respectively.

2. The rate of development appeared to be directly related to sea water temperature and could be modified at any stage by altering sea water temperature. Extrapolations of this relationship are possible, and practical limits of its extension are discussed.

3. Development apparently consisted of four phases; the first three each requiring a specific proportion of the total developmental time independent of temperature and the fourth (hatching), requiring a specific time interval independent of temperature. Development to stage 12 was non-linear and required 13% of the total time. Linear development over stages 12 to 26 required 51% of the total time. Stages 26 to 29 also developed linearly, but required 22% of the total time. In each group, development from stage 29 to stage 30 (hatching) required approximately 52 hr, apparently independent of temperature. Functonal distinctions are suggested for these developmental phases.

4. Approximate time of first hatch could be predicted from the sea water temperature at egg deposition or from an observed time interval between established stages during development.

5. Artificial size distributions constructed from the developmental data and observed sea water temperatures differed markedly from measured size distribution of young squid. Factors other than temperature probably affect the measured size distributon of young squid.