Growth of fish is based on metabolic processes, most importantly anabolism (building molecules and new tissue) and catabolism (breaking down of molecules and old tissue). Modeling growth can be carried out on many different levels of detail. The simplest level is provided by statistical models such as Logistic, Gompertz, Monomolecular, and Richards growth models. Also, the widely used von Bertalanffy model can be classified as a statistically based growth model. More realism is achieved with mechanistically based growth models, where the actual processes underlying growth are modeled, often including bioenergetics. Mechanistically based models often allow growth to differ between the juvenile phase (in which length growth often approaches linearity) and the postmaturation phase (where growth slows down as energy is diverted into reproduction). Mechanistically based growth models thus link closely with the field of life-history evolution, as the dilemma of whether an individual should invest into growth or reproduction lies at the heart of life-history theory. A suite of environmental (e.g., temperature, seasonality, oxygenation) and ecological (e.g., density dependence, anti-predator behavior, sexual selection) factors affect growth and can in principle be modeled. Including more detail in a growth model can improve realism but comes at a cost, for example, in tractability, transparency, or computing time. Consequently, the merits and faults of each modeling approach need to be weighed carefully and the choice of model should depend on the research question at hand.
See also: Body Size, Energetics, and Evolution; Fisheries Management.
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