The direct contribution of fish to lake phosphorus cycles

Published data are synthesised to assess the direct contribution of fish to the recycling of phosphorus across a lake productivity gradient. Phosphorus excretion rates by fish assemblages are more or less directly proportional to fish biomass, despite changes in mean body mass, species composition and diet with increasing lake productivity. Piecewise linear regression of published data shows for the first time that lacustrine fish biomass increases with total phosphorus (TP) concentration in the water column up to around 140 mu g.TP.l(-1) but levels off above that value, suggesting that fish contribute less to nutrient recycling as lake productivity increases. The results confirm previous findings that water column nutrient recycling by fish is much less important than by plankton and that fish are important nutrient stores in lakes. The contribution of fish to nutrient recycling is small because of their low turnover rates relative to other taxa.