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Abstract: Earlier studies have shown that the carotenoid pigmentation in Arctic char (Salvelinus alpinus (L., 1758)) is connected to stress responsiveness. These studies also suggested that the pigmentation is dynamic [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2007.06.007 Byline: Carin Magnhagen, Jost Borcherding Abstract: In fish, predation risk is often size-specific due to gape limited piscivores and visibility constraints. We have investigated whether risk-taking behaviour in perch varies in accordance with size-specific predation risk in their natural habitat. In our two study lakes, the risk of cannibalism was estimated from fishing survey data. In Lake Fisksjon, the relative risk for juvenile perch was much higher than in Lake Angersjon in the early stages, but after reaching a body length of approximately 70mm the situation was reversed, with higher predation risk in Angersjon than in Fisksjon. Groups of perch, from either of the two lakes and of two age classes (0+ or 1+ years), were given the choice of foraging in an open area or hiding in the vegetation in the presence of a predator. Three measures of boldness were estimated: proportion of time spent in the open area, latency to start feeding and duration of first feeding bout. A principal component analysis was used to calculate individual boldness scores from a combination of the behaviour estimates. Differences in boldness scores within age classes corresponded well with the relative attack rates in the two lakes. In the youngest age class, perch from Fisksjon were less bold than those from Angersjon. In the older age class, the Fisksjon perch were bolder than those from Angersjon. Within lakes, boldness differed between age classes. Seemingly, perch adjust risk-taking behaviour to perceived predation risk. Author Affiliation: (a) Department of Wildlife, Fish, and Environmental Studies, Swedish University of Agricultural Sciences, Sweden (a ) Department of General Ecology & Limnology, Zoological Institute of the University of Cologne, Germany Article History: Received 24 April 2007; Revised 28 May 2007; Accepted 5 June 2007 Article Note: (miscellaneous) MS. number: 9374R

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2005.07.017 Byline: Carin Magnhagen Abstract: In the common goby, Pomatoschistus microps, males compete aggressively for nest sites when these are in short supply. I investigated whether prior information about the opponent influenced aggression levels during nest competition. Males that, through a one-way mirror, had been observing two other males compete for a nest were placed together with either the winner or the loser. The new male pairs also received nest sites to compete for, and their behaviour was videorecorded. As a control, naA[macron]ve males, which had not been watching the earlier contest, were also recorded when competing with previous winners or losers. Both bystanders and naA[macron]ve males acquired the nest more often when competing with a loser than with a winner. The male that got the nest was generally more aggressive than his opponent. However, in trials with bystanders and losers, the male obtaining the nest was less aggressive than in contests between bystanders and winners and in contests between naA[macron]ve males and losers. Furthermore, when bystanders competed with losers, they were less aggressive than were naA[macron]ve males competing with losers. There was no difference in aggression between bystanders and naA[macron]ve males competing with winners. Information about the opponent did not increase the probability of obtaining the nest, but the benefit, when applicable, might instead have consisted of a decrease in aggression, and thus a lowered energetic cost of nest competition. Author Affiliation: Department of Aquaculture, Swedish University of Agricultural Sciences, UmeA[yen] Article History: Received 14 March 2005; Revised 4 May 2005; Accepted 3 July 2005 Article Note: (miscellaneous) MS. number: 8495R

Few studies have examined multiple life-history traits across a latitudinal gradient to test whether variation in growth rate and mortality schedules induces trends predicted by life-history theory. We collected data for the following life-history traits for 75 Eurasian perch (Perca fluviatilis) populations: growth coefficient (K) and asymptotic body length ([L.sub.[infinity]) from the von Bertalanffy growth model, size at ages one and two years, specific juvenile growth rate, instantaneous adult and juvenile mortality rates, life span, age and length at maturity, and reproductive life span and investment. All life-history traits except [L.sub.[infinity] were significantly correlated with latitude. In general, growth rates, mortality rates, and reproductive investment decreased with latitude, whereas age at maturity, size at maturity, and life span increased with latitude. Populations could be grouped into two categories based on variation in [L.sub.[infinity]: stunted (small sized) vs. piscivorous (large sized). Four trait-latitude relationships differed between these two types: the growth coefficient (K) and the juvenile growth rate were larger, and age and length at maturity were lower in the stunted populations compared with piscivorous populations. Perch from southern populations tend to grow fast and experience high juvenile and adult mortality rates. As predicted from life-history theory, this selects for an early age and small size at maturity and relatively large investment in reproduction. The opposite pattern was found for northern populations. Key words: latitudinal cline; life-history variation; trade-offs; Perca fluviatilis L.; perch.

Research of the Swedish FiRe project, Reproductive Disturbances in Baltic Fish, investigates the M74 syndrome and the high morality rate of offspring of Atlantic salmon (Salmo salar). The cause of M74 is not yet known, but the symptoms indicate similarities to Early Mortality Syndrome exhibited by salmonids from the North American Great Lakes. A combination of factors are believed to contribute to M74 including ecological changes in the food chain and the Baltic Sea. Naturally spawning populations of Baltic salmon are at risk of extinction because it is impractical to successful bathe them in thiamine which has been found to cure afflicted fry in Swedish hatcheries.

An experiment wherein male common gobies either spawned alone with a female or with a sneaking male present was conducted to determine whether males treat their offspring differently according to confidence of paternity. No differential treatment of their brood was observed, whether males experienced sneaking or not, with estimates of nest defense, fanning rate and parental care the same for the two treatments. No difference in filial cannibalism was likewise noted between the two groups.

The influence of sex ratio on the reproductive behavior and mating success of Pomatoschistus minutus was investigated. The results showed that sex ratio rather than density caused differences in the intra-sexual behavior of both males and females. It was also shown that changes in the sex ratio caused changes in the competition for mates and that individuals adjusted their mating behavior according to the sex ratio.

A study of the influence of predation on the nesting and sneaking behavior activity of male goby fishes reveals that predation suppresses the aggression and sneaking activities of male goby fishes. The common goby males build nests to attract females and protect the nests until the eggs hatch. Small males, unable to build nests, sneak into the nests of other males and fertilise some of the eggs. Original nest builders attack and chase away the intruder males. The aggressive behavior of the owner male depends upon the predation risk.

Certain non-territorial small male common gobies, Pomatoschistus microps, exhibited alternative spawning techniques to enhance their reproductive success before growing large enough to successfully compete for nest sites and females. The body length of nest-holding males correlated to the number of eggs and nest size. Ontogenic development was responsible for the behavioral differences in male common gobies.

Competition among male sand gobies for nest sites is discussed. Aggression level variations for nest sites in case of earlier information about opponents are analyzed.

A study is conducted on groups of four similar - sized - young of the year Eurasian perch, Perca fluviatilis, to analyze the influence of predation risk to their individual competitive ability and growth. It is observed that predation risk does not affect growth variations in the groups.

Nest site availability appears to be a significant factor for courtship roles and mating competition in the common goby. This research has demonstrated how a change in sex-roles produced by an environmentally induced change in sex ratio can be created in the field.