Egg development and control of the gill parasite, Salmincola salmoneus, on Atlantic salmon kelts ( Salmo salar) exposed to four different regimes of temperature and photoperiod

Abstract

Atlantic salmon kelts ( Salmo salar) infected with copepod gill parasites ( Salmincola salmoneus) were kept in freshwater under four different regimes of temperature and photoperiod from January to October 1985. Egg development of S. salmoneus took over 3 months at 1–4°C with an ambient photoperiod. There were two peaks in egg production under this regime, one in May and another less distinct peak in August. At 7°C, with an advanced photoperiod, egg development took approximately 2 months and there were two peaks in egg production, one in March and the other in July. Egg development at 12°C with an ambient photoperiod took approximately 4–6 weeks and three peaks in egg production occurred: one in March, June and August. Since the same pattern of egg production was found at 12°C with an advanced photoperiod, temperature was determined to be the more important environmental variable affecting S. salmoneus egg production. Manual removal of S. salmoneus from the gills of salmon was found to be an effective control procedure if repeated regularly until no further adult copepods could be detected. Since copepod egg production was retarded and reinfection reduced in water temperatures of 2–3°C, it was suggested that manual removal efficiency would be enhanced by holding infected salmon at low temperatures until the copepods were removed.