This paper describes the gravel type and structure of brown trout spawning gravels in Teesdale, the flow characteristics of the spawning sites and the size of redds. Factors influencing redd size are investigated and it is concluded that female size is a major factor.Relationships are established between various redd characteristics and the fork length of female fish. The findings are discussed in relation to the existing literature concerning salmonid spawning sites.

The downstream movement of young trout and salmon in relation to water velocity was studied in simulated river channels. The results are interpreted as showing that these young salmonids pass through a short period when they are very vulnerable to downstream displacement by flow. Behavioural differences between the two species are considered with the influence on fish movement ofchanging rate of water velocity, light and temperature.

Trout eggs were planted in four experimental stream channels, each channel being run at a different but constant discharge. Survival of the eggs to hatching was low and apparently unrelated to surface water velocity. However, movement of young trout out of channels was affected by water velocity, the higher the velocity the greater the proportion of trout that were lost. Virtually all fry moved out of a channel with a mean surface water velocity of 0.73 m s-'. The rate of loss was not constant over the experiment but increased as the young trout entered the free-feeding stage. At the end of the experiment loss of fry, after abrupt increases in discharge, was demonstrated in the lower velocity channels.

Development of bimodality in the length frequency distributions of sibling juvenile Atlantic salmon, Sulrno sulur L., was observed in three experiments, using eight families in 25 tank populations. Divergence between the groups became evident in late summer or early autumn. The time of divergence, and the size of fish at which this change took place differed between families.

Changes in the growth of fish are reflected in the rate of growth of their scales. This produces the rings used in ageing temporate species. A technique has been devised for measuring the rate at which [14C] glycine is incorporated into isolated scales in vitro.This method has been used to investigate various rhythmic activities in fish growth. The results show that the amino acid is incorporated into at least two types of cell and that deposition in the scale occurs with at least two different rhythms with very different frequencies.