Factors influencing carbon, nitrogen, and phosphorus content of fish from a Lake Superior coastal wetland

The narrow fish nutrient ranges (C, 42.8-48.4%; N, 9.6-12.7%; P, 1.91-2.74%) in this study suggest that overall mean values are adequate for quantifying movement of C, N, or P as part of fish-mediated nutrient transport. We measured C, N, and P in 20 species of Lake Superior coastal wetland fish to better understand variability in fish elemental content caused by differences in species, habitat, season, life stage, or size. Fish were sampled within Bark Bay slough and at its inlet/outlet to Bark Bay, Lake Superior, from May to November 1995. Elemental content averaged across all fish (n = 192) was 45.1% for C, 11.3% for N, and 2.45% for P. We did find significant differences (p ≤ 0.05) among nine tested species. However, less than one third of the analyses were significant for effects of location or date of capture or fish length on fish nutrient content and nutrient ratios. Regressions of N:P ratios against growth rate indices and, separately, fineness ratios were significant, suggesting that growth rate and body shape are important factors driving N:P ratios in fish.