Influence of nutrient enrichment on the growth, recruitment and trophic ecology of a highly invasive freshwater fish.

Abstract

The establishment probability of introduced alien fish can be context dependent, varying according to factors including propagule pressure and biotic resistance. The influence of nutrient enrichment on establishment outcomes of alien fishes is uncertain, yet this is a common anthropogenic stressor of many freshwaters. Here, the small-bodied alien topmouth gudgeon Pseudorasbora parva was used in mesocosms to experimentally test how a gradient of nutrient enrichment affected their growth rates, recruitment and trophic ecology. A ‘Control’ represented ambient, mesotrophic conditions, while treatments covered three levels of nutrient enrichment: Low (eutrophic), Medium (hypertrophic) and High (very hypertrophic). Each mesocosm was seeded with 6 mature P. parva (equal sex ratio) at the start of their reproductive season. After 100 days, length increments of the adult fish were significantly elevated in the Low treatment, and these fish had also produced significantly higher numbers of 0+ fish compared to all other treatments. The trophic niche width of the mature fish was substantially higher in the Control than the treatments, but this did not appear to confer any advantages to them in somatic growth rate or reproductive output. These results suggest that the nutrient status of receiving waters can have substantial impacts on the outcomes of fish introductions, where eutrophic conditions can assist the rapid population establishment of some alien species.