SOME EFFECTS OF APPLICATION OF MECHANICAL-SHOCK AT VARYING STAGES OF DEVELOPMENT UPON THE SURVIVAL AND HATCHING TIME OF BRITISH SALMONID EGGS

A standard mechanical shock, by dropping, was applied to eggs of brown trout (Salmo trutta L.) and Atlantic salmon (S. salar L) at several different stages of development to assess variation in sensitivity to mechanical shock during the course of development. Other experiments tested the effect of drifting along 10 m of experimental channel upon the survival of trout eggs at two stages of development. Survival to hatch in control batches of trout eggs and in batches which were given pre-shock handling but which were not shocked was generally high (c. 95%) and application of shock soon after fertilisation and water-hardening or after 'eyeing' had little effect on survival. Trout eggs suffered mortality of 50 to 60% when given a shock of c. 8000 ergs at between 10 and 20% completion of development to median hatch. Observations on Atlantic salmon eggs suggested a similar pattern but were not conclusive. Trout eggs which drifted 10 m in an experimental channel at 10-20% completed development to median hatch suffered 45-56% mortality - similar to the rate observed in eggs given a shock of c. 8000 ergs. Similar drifting at 60-70% completed development to median hatch had no detectable effect on survival. There is some evidence that application of mechanical shock to trout eggs by dropping or by drift can sometimes modify hatching date. © 1990 Kluwer Academic Publishers.