An experimental investigation of the 'match/mismatch' hypothesis using larval Atlantic cod

Abstract

The match/mismatch hypothesis suggests that the degree of overlap between larval fish and their prey affects larval growth, survival and recruitment. For example, some fish species have a relatively fixed spawning period while peak production of their food varies yearly, depending on abiotic factors, creating a match or mismatch between the two In this study, we investigated the influence of a match or mismatch on growth of cod (Gadus morhua larvae. Larvae were exposed to 1 of 5 different 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 and 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. Larvae 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 tinder 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 than 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 treatments. Larvae under the LF-HF treatment were significantly larger than those 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 highest when larvae were exposed to a HF level. A switch between LF and HF resulted in a significant increase in specific growth rate in the LF-HF treatment and decrease in the HF- LF treatment. The number of larvae surviving to Day 35 post-hatch, and through to metamorphosis, was highest for the HF treatment, followed by the LF-HF, HF-LF, and LF treatments. Our results suggest that a mismatch and its timing can significantly influence the growth and survival of cod larvae.