On the ecology of spined loach in Lake Muggelsee

The growth, density and diet of a lacustrine diploid- polyploid- complex of spined loach was investigated. The recruitment of juveniles was irregular due to the dependence of reproduction on filamentous algae. If compared to literature data, the growth was rather fast but varied between the years; p ossibly the lack of young age classes led to differences in density depende nt factors influencing the growth. After appearance in spring the fish beha ved stationary with only single mobile individuals. During this period, the distribution at the shore was very irregular. In autumn the animals disapp eared from the shallow shore area. The fish fed exclusively upon benthic or ganisms and showed a special size spectrum of ingested items. No difference s between the genetic forms concerning the investigated aspects were found. This indicates a high niche overlap between the levels of ploidy, which sh ould lead to strong competative interactions. The fragile structure of the population- complex can be described as a sexual parasite- host interaction .