Growth of Young-of-the-Year and Yearling Centrarchids in Relation to Zooplankton in the Littoral Zone of Lakes

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Abstract
Correlations were determined between the growth/body condition of centrarchids age 0+ to 1+ and the abundance of specific taxa of zooplankton in the littoral zone of 3 lakes in piedmont North Carolina [USA] over a period of 8 mo. Stomach analyses were conducted, and electivity indices were calculated to provide comparative data. Body condition, growth rate, and zooplankton abundance were significantly different between lakes (P < 0.05, ANOVA [analysis of variance]). First year growth and changes in body condition of age 0+ for Lepomis, Pomoxis and Micropterus spp. were positively correlated with the abundance of copepod nauplii and copepodids in each lake (mean rs = 0.898, P < 0.01). The abundance of adult copepods was also frequently correlated with growth and body condition, but at a lower level of probability (mean rs = 0.713, P < 0.05). The number of significant correlations dropped sharply as fish age increased to 1+ yr. Significant associations could not be generated using data for Rotifera, Protozoa or Ostracoda, and were infrequent for Cladocera. Copepod nauplii and copepodids are probably primary food during the critical period when larval centrarchids switch from endogenous to exogenous nutrition. The correlation data were supported by stomach analyses and electivity indices which indicated 0+ fishes to be utilizing mainly copepods, supplemented with cladocerans, insect larvae, and fishes in the more piscivorous species. The mean prey size for larval bluegill and largemouth bass (.ltoreq. 15 mm total length) was 0.48 mouth gape and 0.60 mouth gape, respectively, which translates to prey sizes of 0.11-0.35 mm during the larval stage. Due to mouth size during the period of 1st feeding, most adult copepods and cladocerans are too large to be ingested even if prey could be handled with dimensions approaching 0.99 mouth gape. The relative insignificance of Cladocera in the diet of post-larval fishes appears to be due to negative selection rather than to influences of seasonal abundance or encounter probability. In these North Carolina lakes, cladocerans are not so universally important in the diet of age 0+ centrarchids as studies on northern and midwestern lakes would indicate. Correlations, stomach analyses and electivity indices can be integrated into a multiple factor approach to diet studies, allowing consideration of several environmental and population variables and yielding more meaningful results than by using 1 method alone. Potential impacts of aquatic pollution on food organisms required during the 1st weeks of feeding should place additional priority on diet studies and ecological relationships between centrarchids and the littoral zone.

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