Environmental conditions and yolk biochemistry : factors influencing embryonic development in the squid Loligo forbesi (Cephalopoda: Loliginidae) Steenstrup 1856
The squid Loligo forbesi is fast growing, short-lived (c. 1 year) and semelparous, which means that population abundance is determined by recruitment from the previous year. Females of this neritic squid spawn eggs in finger-like strings and attach them to substrata on the sea floor at depths of 100m. In the laboratory the incubation period of single strings ranged from a mean of 33 days at 16oC to 130 days at 8oC. There was significant inter-string variation in the incubation period, e.g. the mean incubation period ranged from 46-64 days at 12oC. Such a range in the time of hatching may enhance survival. Hatching occurred in the dark. The energy content of eggs varied between females and geographical area. Hatchlings from eggs reared at 16oC generally had smaller mantle lengths than hatchlings from eggs reared at 8oC and embryo size was affected by its position within the egg string. The principle component of squid egg yolk was protein (c. 15% wet mass). Lipids were c.2.5% wet mass. The fatty acids eicosapentaenoic and docosahexaenoic acid formed c.45% of the total fatty acids in eggs. There is some evidence that the fatty acid arachidonic acid has an important function during the late embryonic stages. Zinc and copper were the most abundant metals in eggs of L. forbesi. Zinc was more abundant than copper and was probably bound to an egg binding protein of c. 20 KDa. The findings contribute to a greater understanding of the environmental and biochemical factors, which influence the variability in recruitment in loliginid populations and the plasticity of their life cycles.