Early Maturing Males Research Articles

Intra‐ and interspecific life history differences in sympatric grayling and brown trout in a Norwegian reservoir

Grayling Thymallus thymallus in Lake Aursjøen, Norway, showed a remarkably uniform growth pattern throughout life, whereas brown trout Salmo trutta showed far more variation. In addition, a narrower age‐length interval of maturation was found in grayling. The restricted life history variation in grayling is discussed and it is suggested that all grayling of Lake Aursjøen experience similar environmental conditions as juveniles, which induces low phenotypic variation. In contrast the existence of several spawning populations, adapted to as many as 28 different tributaries, may have created large life history variation in Aursjøen trout. Logistic models revealed that both age and length had significant, simultaneous effects on the maturation of both species. Furthermore, the sexes of trout differed in maturation patterns, i.e. males matured earlier and at smaller sizes than female conspecifics, but no difference was found between the sexes of grayling. In addition, larger sex‐specific growth differences were found in trout. An absence of early maturing males in grayling and their presence in trout is discussed as a possible explanation of the restricted life history variation found between sexes of grayling. Male grayling experienced a larger mortality rate than did females, whereas no such differences were found in trout. It is suggested that grayling males invest more in reproduction than do females, due primarily to large investments in breeding behaviour. The equal mortality rates found for both sexes of trout, albeit males starting to spawn earlier than females, is probably explained by a female‐selective fishing mortality.

Growth and Sex Distribution in an Anadromous Population of Arctic Char in Northern Norway

Abstract Presmolt Arctic char Salvelinus alpinus in the River Halselva watershed, northern Norway, were analysed with respect to growth and sex distribution. Two main hypotheses were tested: (1) females dominate among the first-time sea migrants; and (2) age at smoltification depends on presmolt growth rate. Our results showed no significant difference in sex distribution of first-time migrants. There was a low frequency of early maturing males in the population, and no differences between the sexes with respect to early sexual maturation were observed. The first-time sea migrants showed a higher presmolt growth rate than the nonmigrating parr in Lake Storvatn, the only lake of the Halselva watershed. Based on both the low frequency of mature pan and the sex ratio in the smolt run, the population of Arctic char in the profundal zone in Lake Storvatn is predominantly anadromous fish. These fish migrate to sea at a greater age than the first-time migrants observed in the River Halselva and are thus “tempora...

The genetics of age and weight at sexual maturity based on individually tagged rainbow trout ( Oncorhynchus mykiss)

Age and body weight at sexual maturity are important traits for aquaculture as is the relationship between the traits. The genetics of rainbow trout age at maturity (days), an indication of the time of spawning within a season, and body weight at maturity were investigated for two consecutive spawning seasons. The relationship of the maturity traits to each other and to body weight at specific ages was evaluated. During the first spawning season, data were obtained on early maturing males (E-males), mature at an average of 301 days post-fertilization. During the second spawning season, data were collected on females, males mature for the first time (T-males), and males mature for the second time (E-males), mature at an average of 697, 685, and 673 days, respectively. Estimation of genetic parameters was accomplised using an additive genetic and maternal mixed model. Heritability estimates for age at maturity were high, 0.86 and 0.60 for the first and second seasons, respectively. The heritability estimate for body weight at maturity for the first season was also high, 0.89, but was a moderate 0.27 for the second season. For both spawning seasons, there appeared to be little genetic relationship between age at maturity and body weight measured approximately 0 and 2 months before the first mature fish was found. However, the genetic correlation between age at maturity in the second season and body weight measured on the day the last mature fish was found (740 days) was 0.56. The genetic correlations between age at maturity and body weight at maturity within the same season were 0.67 and 0.58 for the first and second seasons, respectively. For both seasons, genetic correlations between body weight at maturity and body weight measured at other specific ages were fairly high, ranging from 0.50 to 0.99. The genetic correlation between body weight at maturity for the first and second seasons was 0.51. Selection to genetically improve body weight from 0 to 2 months before the spawning season should not affect the timing of spawning. However, selection to decrease the age at maturity and alter the spawning season may affect body weight at maturity and thus characteristics of the eggs.

Effects of Elevated Winter Temperature on Seawater Adaptability, Sexual Rematuration, and Downstream Migratory Behaviour in Mature Male Atlantic Salmon Parr (Salmo salar)

In experiments with two different salmon (Salmo salar) stocks, elevated winter temperatures (Celsius) 4–9° above the ambient increased the degree of testicular resorption in previously mature male Atlantic salmon parr. Two-summer-old mature male parr maintained at a temperature 9° over the ambient for 5 mo (January–May) showed an increase in hypoosmoregulatory ability when challenged in seawater at the time of smoltification whereas parr kept at elevated temperature for various 2-mo periods (January–February, February–March, or March–April) failed to show this improvement. Furthermore, previously mature males kept at an elevated winter water temperature for either 2 or 5 mo showed a lower incidence of sexual rematuration, and consequently a higher mean growth rate, after one summer in sea pens. A river release experiment showed that rearing previously mature males at 4–7° above the ambient water temperature from December to April increased the number of downstream migrating fish to a level similar to that of immature smolts. We suggest the use of a simple method for enhancing the potential yield of ranched and cultured salmon from early maturing males by removing them from the stock population and rearing them over winter in heated water.

Mental illness and cognition in relation to age at puberty: a hypothesis.

Onset of puberty is usually considered to coincide with the last major step in brain development: the elimination of some 40% of neuronal synapses. Mean pubertal age has declined by some 4 years during the last 100 years. There is a relation between age at puberty and body build, and between body build and mental illness. The difference in body build between schizophrenia (S) and manic-depressive psychosis (MDP) is similar to that between late and early maturers. It is suggested that S affects late-maturing individuals and MDP very early maturers. The observed marked rise in MDP and decline in the most malignant forms of S (non-paranoid) are in agreement with MDP and S as neurodevelopmental disorders occurring at the extremes of maturation. Maturational irregularities are most likely to occur at the extremes, and it is suggested that abbreviation of the regressive process may have led to persistent redundancy of neuronal synapses in MDP and that prolongation of the process past the optimal has yielded an inadequate synaptic density in S. The lack of cerebral abnormality in the majority of MDP and the presence of only subtle structural deficits in S, are in agreement with this. The two disorders are probably as old as mankind, and early puberty is the necessary factor for the development of MDP and late puberty is the necessary factor for that of S. There is an inverse relation between spatial ability and rate of maturation, whereas verbal ability is unaffected by maturational rate. From a previous predominance in both sexes, spatial ability (Performance IQ scores) has been reduced to below verbal ability (Verbal IQ scores) in the female sex and in early maturing males.

The influence of precocious sexual maturation on survival to adulthood of river stocked Baltic salmon, Salmo salar, smolts

During three consequtive years, 1975–1977, Individually tagged Baltic salmon Salmo salar smolts of sexually immature male and female fish (n = 35027, mean size: 15.2 cm) and precocious males (n = 6518, mean size: 14.2 cm) were released into Umeälven (Ume river), northern Sweden. Rate of survival (% captured adults) based on 3714 recoveries was significantly higher (p < 0.01) for smolts from immature fish (10.2%) than those from smolts of early maturing males, i.e. precocious males (2.2%). corresponding to an average yield of 474 and 85 kg per KHX) smolts released, respectively. Gain in survival was on average 2.5% and 1.4% per cm increase in smolt size for immature smolts and smolts from precocious males, respectively. The poor survival among smolts of precocious males is suggested to he related to an interaction between sexual maturation and smolting linked to incompletely resorbed gonads leading to a non migratory behaviour. These non migratory males are then suggested to suffer heavily by predation in the river.The two smolt categories had a similar growth pattern in sea. Smolts from precocious males did not mature early in sea indicating no relation to grisling, i.e. sexually maturing fish returning after first winter in sea. Adult weight of fish returning the fourth summer after release was related to smolt size (P < 0.05). Our Response Surface Model (RSA) predicted that large smolts (19.0 cm) had a higher specific growth rate over their life‐span compared to small smolts (<15.0 cm), 0.86% d−1 and 0.46% d−1, respectively. Large smolts (19.0 cm) attained a size of 3.0 kg during their second winter in sea about six months earlier than small smolts (13.0 cm). The paper discusses alternative release strategies that can be employed if the ultimate goal of salmon stocking is maximizing yield.