Length-structured Evaluation of Seasonal Energy Patterns in Largemouth Bass

Abstract

ABSTRACT We developed a new approach for evaluating energy dynamics in fish populations and applied it to largemouth bass Micropterus salntoides. Wild fish were collected monthly and primary energy constituents (protein and lipid) were determined for specific tissues (muscle, liver, and gonad). Monthly samples were partitioned into length categories, and sex-specific log,, weight-length regression equations were used to predict weights for the midpoint total lengths of stock to quality (S-Q) and quality to preferred (Q-P) length categories (250 and 340-mm TL for S-Q and Q-P fish, respectively). These weights then were adjusted by using the monthly relative weight (Wr) means of sex and length categories as correction factors to adjust for seasonal changes in plumpness to arrive at a representative monthly weight for each category. Monthly lipid and protein fractions of tissues then were multiplied by mean muscle, gonad and liver weights of these standard fish to obtain lipid and protein weights. Energy equivalents were applied to provide total energy estimates of the lipid and protein quantities. The approach provided a unique method for evaluating population energetics allowing direct comparisons among sex and length categories. INTRODUCTION Bioenergetics has been a popular topic in the fisheries literature for the last two decades (e.g., Adams and Breck 1990). Such studies have been conducted with a variety of applications in mind, but changes in seasonal energy content have been rarely compared with responscs in condition or tissucs. Additionally, distinction between crude energy fractions (i.e., lipid and protein) is important for the determination of energy dynamics because other methods, such as bomb calorimetry, provide total energy estimates and therefore may not provide an accurate account of energy fraction dynamics. For example, in the present study total energy content of gonad tissue for female stock to quality-length (200 to 299-mm total length), largemouth bass Micropterus saln~oides was nearly equivalent for November (3.49 kl) and March (3.42 kJ); yet, upon examination of the energy fractions, lipid energy comprised 22 and 43% of November and April determinations, respectively. Thus, calorimetry results would not adequately describe the energy dynamics that occur in translation of the lipid energy into gonadal products. Similarly, studies conducted on the proximate composition of whole body do not account for translocation of energy constituents. Therefore, the present study describes seasonal energy patterns in terms of lipid and protein dynamics of major tissues in largemouth bass.