Effects of temperature on yolk utilization by chokka squid (Loligo reynaudii d'Orbigny, 1839) paralarvae

The effects of temperature on the utilization of yolk by chokka squid (Loligo reynaudii d'Orbigny, 1839) paralarvae was studied for starved animals at 12, 16, 18 and 19 °C. This range encompasses temperatures which naturally occur on the inshore (warm) and mid-shelf (cold) spawning grounds located on the Agulhas Bank, South Africa. Eggs were collected by SCUBA divers on the inshore spawning grounds (St. Francis Bay) and incubated in the laboratory at 15.6 °C and 14.4 °C in January–February 2007 and January 2008, respectively. Mean mantle length (ML), wet weight (WW) and yolk weight (YW) for paralarvae incubated at 14.4 °C were 2.58 mm, 2.06 mg and 0.27 mg, respectively. Paralarvae incubated at 15.6 °C had 2.43 mm ML, 1.96 mg WW and 0.21 mg YW. Mean dry weights (DW) were 0.47 mg at 15.6 °C and 0.38 mg at 14.4 °C. Yolk was exponentially utilized with paralarvae maintained at warmer temperatures utilizing their yolk faster and surviving less than their counterparts at colder temperatures. Survival time predicted using exponential and linear yolk utilization rates approached experimental values (with 80% mortality) only at 12 °C. The implications for paralarval dispersal, recruitment and the inshore and mid-shelf spawning grounds are discussed.