Biphasic growth in fish I: theoretical foundations.

Area of Science:

• Aquatic Ecology
• Fish Biology
• Theoretical Ecology

Background:

• Fish growth is often modeled using the von Bertalanffy (vB) function, which may not fully capture complex life-history changes.
• Understanding energy allocation is crucial for accurate fish growth modeling, especially concerning reproduction.

Purpose of the Study:

• To develop and analyze biphasic somatic growth models for fish.
• To investigate the influence of energy allocation and reproductive strategies on growth patterns.
• To compare the performance of biphasic models against the traditional vB model.

Main Methods:

• Development of a 'generic biphasic' (GB) model incorporating pre- and post-maturation growth stages.
• Derivation of an explicit expression for the gonad weight/somatic weight ratio (g).
• Construction of optimal biphasic growth models (fixed g and variable g) to maximize lifetime reproductive output.

Main Results:

• Pre-maturation growth is linear in both optimal biphasic models.
• Adult growth approximates the vB form under fixed gonad-somatic weight ratio constraints and nearly so without constraints.
• Biphasic models demonstrate advantages over the vB model in fitting data and parameter interpretability, as shown with lake trout data.

Conclusions:

• Biphasic growth models provide a more nuanced and accurate representation of fish growth dynamics.
• Energy allocation strategies significantly impact fish growth trajectories and reproductive output.
• The developed biphasic models offer superior explanatory power for fish growth compared to the standard vB model.