Observations on the morphology, behaviour and salinity tolerance of downstream migrating River lampreys (Lampetra fluviatitis)
Potter, I.C. and Huggins, R.J. (1973) Observations on the morphology, behaviour and salinity tolerance of downstream migrating River lampreys (Lampetra fluviatitis). Journal of Zoology, 169 (3). pp. 365-379.
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Downstream migrating Lampetra fluviatitis were caught at night in elver trawls from the lower reaches of the River Severn during the high spring tides of 1970,1971 and 1972. The length and weight-frequency curves indicated that in 1970 and 1972, the populations consisted mainly of animals of single year class. On the basis of previous estimates of the duration of larval life, they were thus probably five years old, while a small group of larger animals may have been one year older. In 1971, there was a greater proportion of larger animals, several of which differed in their weight/length relationship from others in this sample and from those of 1971 and 1972, possibly reflecting differences in feeding conditions during larval life. Laboratory studies on the activity rhythms of downstream migrants showed that emergence from the substrate and swimming was primarily nocturnal, with an initial large peak in free-swimming activity at the onset of darkness and a smaller peak at the transition from the dark to the light phase. During the light period, these animals showed a significant preference for burrowing or lying in regions of gravel and pebbles. Downstream migrants examined in May/June 1972 were capable of being acclimated to full strength sea water (34–35°/00) and a large proportion (80%) survived for three weeks or more after direct transfer. Parallels are drawn between the biology of this stage in the lamprey life cycle with that of similar stages in salmonid fishes.
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