At the edge of the thermal window: effects of elevated temperature on the resting metabolism, hypoxia tolerance and upper critical thermal limit of a widespread African cichlid
This study explores costs of mouth brooding and the response of parent and offspring to brooding under hypoxia in the maternal African mouth brooder Pseudocrenilabrus multicolor. Fish of swamp origin were acclimated to hypoxia (1.42 mg oxygen L(-1)) or normoxia (8.00 mg oxygen L(-1)) for a minimum of 6 months prior to measures of metabolic rate and embryo traits. Regardless of brooding stage, standard metabolic rates were lower in females acclimated to low dissolved oxygen (DO) compared to high-DO acclimated females. Regardless of DO acclimation treatment, standard metabolic rates were approximately 48% higher in brooding females (with the estimated metabolic rate of the brood removed) compared to post-brooding females. There was no difference in brood maintenance metabolism, female relative condition, embryo size, and embryo number between fish acclimated to low DO vs. high DO. However, the length of the brooding period (from egg-laying to release of fry) was approximately 27% shorter in females acclimated to low DO compared to females acclimated to high DO suggesting accelerated development in offspring brooded under hypoxia. These findings demonstrate a cost to mouth brooding and provide evidence for a parental strategy to deal with the expense of providing offspring care under hypoxia.