Differences between marine and freshwater fish larvae: implications for recruitment

Abstract

Differences in the dynamics (growth and mortality) and energetics properties of marine and freshwater fish larvae have important implications for determining the life stages at which year-class size is established. After correcting for temperature effects, marine fish larvae, which typically weigh less at hatch, can be shown to experience mortality rates, have higher metabolic requirements, and have longer larval stage durations than do freshwater fish larvae. Growth rates and growth efficiencies are similar for the two categories of larvae. The difference in body size between typically small marine and typically large freshwater fish larvae is an important factor affecting their dynamics and energetics. Predicted mean survivorship to metamorphosis of a cohort of freshwater fish larvae is 5.30%, while that of marine larvae is only 0.12%. The probability of significant density-dependent regulation during the larval stage could be relatively high for marine species, based upon their life-history properties. The probability that episodic mortalities of larvae will have significant impacts on recruitment may be higher for freshwater fish than for marine fish. Starvation mortality is more probable for marine larvae, primarily because of their small body size, associated high metabolic demands, and possibly higher ingestion requirements. Because expected mean survivorship of freshwater larvae is 44 times higher than that of marine larvae, juvenile-stage dynamics will be relatively important in controlling/regulating recruitment levels of freshwater fishes. In contrast, properties of marine species indicate that larval-stage dynamics will have a greater influence on recruitment success.