Size-based competition explains large inter- and intra-individual variation in both intake and growth

Area of Science:

• Comparative Physiology
• Animal Ecology
• Bioenergetics

Background:

• Intraspecific competition, particularly size-based, causes significant variation in feed intake and growth in fish.
• Disentangling competition effects from other environmental factors on fish physiology and growth is complex.

Purpose of the Study:

• To quantify the impact of size-based competition on fish feed intake and energetic costs.
• To model the body mass-dependent scaling of feed intake and living costs using bioenergetics.

Main Methods:

• Analysis of a longitudinal dataset with individual feed intake and growth data from 543 fish.
• Utilized relative body size as a proxy for competitive ability.
• Integrated relative body size into a bioenergetic model to estimate scaling effects.

Main Results:

• Incorporating relative body size into the bioenergetic model significantly improved its fit and replicated observed size variation.
• Size-dependent competitive interactions were identified as key drivers of size-at-age variation, even in controlled settings.
• Suppressed growth in smaller fish was primarily linked to increased energetic costs of living, rather than reduced feed intake.

Conclusions:

• Size-based competition is a crucial factor influencing individual growth trajectories in fish populations.
• Energetic costs of living play a more significant role than feed intake reduction in explaining growth disparities among fish of different sizes.
• Understanding these size-dependent dynamics is vital for managing fish populations and aquaculture.