The effect of the reef of the first floating salmonid farm on the Bicaz Reservoir

Summary

The immersed surfaces of a salmonid floating cage farm has a reef effect, materialized as follows: periphyton development is strengly stimulated so that it becomes an abundant trophic resource; — these immersed objects are new territories of refuge, playing and spawning for native fish fauna; — they are also a continuous source of nutrients for the lake and this may lead top accelerated eutrophication if the extent of aquaculture exceeds the limits of self-purifying capacity. On the Bicaz water power reservoir (max. surface 3,000 ha, length 36 km and max. depth -92 m) there is a floating farm for industrial rearing of rainbow trout (Salmo gairdnen). Its total area is 1 ha and the production capacity 100 t · ^-1. The submerged surface of the farm is about 45,000 m², consisting mainly of the surface of the cage net. Some previous studies showed the periphyton biomass ranged between 1,500-3,700 mg dry matter · m^-2 · month^-1. In order to determine the influence of this artificial reef on the native fishes, two special equipments were used; they allowed direct ethological observations between 0–6 m. One of it was placed among the cages and the second in a control station. Results: The labyrinth of the artificial reef is permanently inhabited by a bleak population (Albumus albumus); it uses the cage net for spawning; during summertime large crowds of Abramis brama, Chondrostoma nassus and Gobio gobio were observed here; related to these, an increased density of several free predatory fishes, esp. native grown Salmo gairdneri was noticed.