A Bioenergetics‐Based Approach to Explain Largemouth Bass Size in Tropical Reservoirs

Abstract In tropical systems where largemouth bass Micropterus salmoides have been introduced, maximum age is reduced to the point where few fish live beyond 3 years and adult growth rates are very slow. Concurrently, tropical largemouth bass have an extended spawning period (up to 8 months) and individual fish spawn multiple times each year. In this study, we examined the relationship between latitude and maximum size (record angler‐caught fish) of largemouth bass from temperate to tropical environments and tested the hypothesis that the slow growth of adult largemouth bass is the result of excessive energy reallocation to reproduction. State and national record‐sized largemouth bass were plotted against latitude for the USA, Cuba, Dominican Republic, Japan, Portugal (European record), Mexico, and Puerto Rico. Largemouth bass maximum weight increased as latitude decreased from 46.8°N; peak maximum weight occurred at 27.9°N. Below 27.9°N, largemouth bass size records decreased as latitude decreased ( R 2 = 0.67, P < 0.0001). Bioenergetics models were used to model observed growth (in Puerto Rico) and predicted growth based on a 2% mean daily ration (MDR), and reproduction scenarios were used to explain the difference between observed and predicted growth. The predicted weight in Puerto Rico was 2.7 times higher than observed weight during a simulated 6‐month spawning season. This discrepancy could be accounted for by a range of spawning frequencies (events per season) and levels (percent body weight per spawn) for females (e.g., 10 spawns at 6% body weight per spawn). Similarly, a 15% decrease in MDR of nest‐guarding males due to reduced ability to feed accounted for the difference between predicted and observed growth.