The effects of a settled industrial domestic sewage works effluent from percolating filters on the embryo viability and hatching success of rainbow trout, Salmo gairdneri Richardson

Abstract

The mortalities of washed and unwashed rainbow trout embryos exposed to Birmingham tap water, 50% and 100% settled efAuent from filter beds has been compared. Differences in the hatching success between washed and unwashed embryos in the three treatments were also compared and the effect of saprophytic microbial growths assessed. There was a significant difference in mortality between washed embryos exposed to tap water (5%) and 50% emuent ( I 2%) and 100% emuent (12%) when dissolved oxygen levels were maintained near 100% air saturation value. Mortalities of unwashed embryos were 4%, 26%, and 26% respectively for the three treatments. Hatching success of washed embryos was similar in the three treatments but unwashed embryos were significantly affected by the etlluent treatments because of Sphaerotilus growths.