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No description available.

No description available.

The reproductive characteristics of a wide range of freshwater-resident and anadromous Scottish forms of Salmo trutta were examined. A total of 653 females were sampled from 27 wild and two long-term domestic populations covering a fork length range of 116-725mm. Total fecundities of the wild fish were 51-5952 eggs. Egg diameters ranged from 3.6 to 6.4mm. Gonadosomatic indices ranged from 5-26%. The youngest females were 2+ years. Trout from fast-growing populations matured earlier and were shorter-lived than slow-growing trout. Regression equations for the relationship between body size and fecundity and egg diameter are provided for the national data set and for individual and grouped populations. Significant differences in fecundity and egg diameter were found between populations. After standardisation to a common body length, fecundity and GSI were found to be positively and egg diameter negatively correlated with trophic status of the water bodies and with early growth rate. The domestic populations provided the overall highest relative fecundities and smallest egg diameters. Fecundity of wild trout was negatively and egg diameter positively correlated with latitude. There was no relationship with numbers of other fish species present. Above-falls trout were short-lived, yet had high relative fecundity and small egg size. In these populations, age was more important than length in determining egg diameter. The rate at which maturity is reached, varying between populations, may be more important than absolute growth rate in determining fecundity and egg size. Lifetime eggs per female and instantaneous production by 1000 females were estimated for individual populations. The significance of the estimates for the River Ewe System in north west Scotland, an area of recent sea trout population decline, is discussed.

The environment under which fish are maintained as broodstock before reproduction is often stressful; however, the impact of stress on broodstock and gamete quality is not well known. We investigated the effects of stress over the final stages (i.e. the 3 months preceding ovulation) of sexual maturation of female rainbow trout, Oncorhynchus mykiss, on their reproductive performance and physiology and that of their progeny. Stress was administered over the period of early vitellogenesis (one and a half months), late vitellogenesis-final maturation (one and a half months), or during both periods (three months). Each stress treatment and control was triplicated with eight females in each replicate (n=24 fish per treatment). The eggs and progeny of each female were kept separate and observations made for four months after transfer to rearing tanks. Cortisol levels were measured in plasma, ovarian fluid and eggs by radioimmunoassay. Fish that experienced stress during final maturation and those that were under stress during the whole experiment spawned on average two weeks earlier than the control group. In contrast, fish stressed during the period of early vitellogenesis spawned at the same time as the controls. Absolute fecundity and fertilization were not significantly affected in any treatment group; however, significant differences were found in relative fecundity. Stress applied early in vitellogenesis resulted in smaller eggs and swim-up fry; but, these differences were not found in juveniles 8 weeks after hatching. Furthermore, we found no differences in survival of the progeny or resistance to the fish pathogen Vibrio anguillarum. Circulating levels of cortisol were high at ovulation in all groups, but significantly less cortisol was observed in the ovarian fluid and eggs. Sex hormone concentrations were high in plasma; however, they were several orders of magnitude lower in the ovarian fluid. These differences were not as extreme as those observed for cortisol. Lower levels of cortisol and sex steroids in ovarian fluid and eggs compared to that which is available from plasma suggests that there is a mechanism by which the female protects the eggs from potentially deleterious effects of prolonged exposure to elevated concentrations of steroids. / Graduation date: 1996