AN EXPERIMENTAL INVESTIGATION OF THE MATCH MISMATCH HYPOTHESIS USING LARVAL ATLANTIC COD

The match/mismatch hypothesis suggests that the degree of overlap betw een larval fish and their prey affects larval growth, survival and rec ruitment. For example, some fish species have a relatively fixed spawn ing period while peak production of their food varies yearly, dependin g on abiotic factors, creating a match or mismatch between the two. In this study, we investigated the influence of a match or mismatch on g rowth of cod (Gadus morhua) larvae. Larvae were exposed to 1 of 5 diff erent food treatments: (1) high food (HF) (match); (2) low food (LF), (3) HF then LF (HF-LF), and (4) LF then HF (LF-HF) (2, 3 & 4 mismatch) ; and (5) no food (NF) (complete mismatch). In treatments including a switch in food level, the switch took place on Day 11 post-hatch. Larv ae were sampled every 5 d, and standard length, body depth, dry weight , and gut fullness recorded. Specific growth rate (% dry wt d(-1)) of larvae reared under the different food treatments was calculated. The experiment was repeated to examine the influence of Treatments 1 to 4 on survival of larval cod. All larvae in the NF treatment died by Day 20 post-hatch. Larvae under HF conditions were significantly larger th an those in all other treatments by Day 20 post-hatch, while at Day 35 , there was no difference between larvae from the HF and LF-HF treatme nts. Larvae under the LF-HF treatment were significantly larger than t hose from the HF-LF and LF treatments by Day 30 post-hatch. There was no significant difference in size between larvae from the HF-LF and LF treatments throughout the experiment. Specific growth rate was highes t when larvae were exposed to a HF level. A switch between LF and HF r esulted in a significant increase in specific growth rate in the LF-HF treatment and decrease in the HF-LF treatment. The number of larvae s urviving to Day 35 post-hatch, and through to metamorphosis, was highe st for the HF treatment, followed by the LF-HE HF-LF, and LF treatment s. Our results suggest that a mismatch and its timing can significantl y influence the growth and survival of cod larvae.