The use of bioenergetics models in fisheries ecology and management has increased rapidly in recent years, but application‐specific information on energy content of fish and their prey has lagged behind. We believe this is because the process of directly measuring energy density is very time consuming. In this paper we present and evaluate a series of general empirical models that predict energy density (J/g wet weight) from fish percent dry weight. Data were gathered from the literature, obtained from cooperating investigators, and measured directly. Least‐squares models were derived for all species combined and for orders, families, and species. All models were linear; however, logarithmic transformation was necessary to normalize residuals in the combined model. All models with more than four data points were highly significant (P < 0.002) and had coefficients of determination of 0.76 or greater. The model for all species combined (N = 587, r2 = 0.95) was J/g wet weight = 45.29 DW1.507; DW is the percent dry weight of the fish. At all taxonomic levels, energy density models showed a strong positive relationship between energy density and percent dry weight. This relationship, if corroborated, should allow the estimation of seasonal and ontogenetic changes in energy density based solely on percent dry weight data.

The need to precisely measure growth is a common denominator in many fisheries studies, but growth measures other than total masses or lengths are nearly nonexistent because more precise measurements such as body composition analysis are often too difficult and time consuming. Here, we present a means of estimating body composition in fish quickly, and after validation, without the need to sacrifice the animal. Models built with brook trout (Salvelinus fontinalis) were linear with strong validation group relationships (R2 > 0.96) for composition parameters including water, protein, fat, fat-free, and dry masses. Subject responses to bioelectrical impedance analysis were minimal, with only slight bruising (p < 0.001) with no effect on swimming, color, bleeding, or feeding. The model was also tested on the water and dry masses of 10 warmwater fish species and found to have strong correlations (R2 > 0.86), suggesting that more general relationships may exist. Nonlethal estimation of body composition using bioelectrical impedance analysis will permit increased precision in bioenergetics energy flow and compositional studies as well as permit study of community energetics and condition on spatial and temporal scales not previously possible.

No abstract

Bioenergetics models for striped bass (Morone saxatilis), bluefish (Pomatomus saltatrix), and weakfish (Cynoscion regalis) were developed from laboratory experiments on metabolism and consumption. Size-specific rates of consumption and metabolism were similar for bluefish and weakfish and higher than those for striped bass. Temperature effects on maximum consumption rate (Cmax) differed with fish size. Cmax of young fish (30 g) increased with temperature, then declined rapidly at higher temperatures; Cmax for larger fish of all three species (100–3000 g) increased rapidly to the maximum rate, but leveled off at higher (25–30 °C) temperatures. Results of Cmax experiments suggest that extrapolation of the temperature dependency of small fish to larger fish, as is commonly done, may misrepresent potential growth at higher temperatures. Independent model validation using laboratory experiments found consumption estimates (from growth) to be within −1.4 to +4.5% of known values for all species at temperatures above 19 °C; however, at 6.9°C consumption by striped bass was overestimated by 20–46%. Model estimates of growth (from consumption) were within −7.1 to +30.1% of known values in all validations. Overall, the growth physiology of the three species appeared to be related to the water temperatures encountered during estuarine residency and production.