Hannu Huuskonen

Metabolic depression and spleen and liver enlargement in juvenile Arctic charr Salvelinus alpinus exposed to chronic parasite infection

The present study on the connection between standard metabolic rate (R(S)) and chronic Diplostomum spp. infection resulted in a decrease in R(S), and an enlargement in spleen and liver sizes in the infected juvenile Arctic charr Salvelinus alpinus compared to control fish. As splenic enlargement observed in infected fish was not due to condition-related changes in the spleen, it could most probably be explained by increased leucocyte synthesis. The higher liver masses in infected S. alpinus may have been related to disorders in energetic function, which could have had major effects on biochemical regulation by the liver. The proposed metabolic syndrome with a possible reduction in insulin sensitivity in tissues results in ineffective glucose and lipid metabolism and thus it is suggested that chronic Diplostomum infection in S. alpinus might not impose direct energetic costs, but it may weaken the efficiency of energy metabolism and thus lead to lowered R(S).

Both male and female sexual ornaments reflect offspring performance in a fish.

Secondary sexual characters are often expressed in both sexes (mutual ornamentation), but are less often studied simultaneously. We studied the adaptive signaling function of male and female ornamentation in a mutually ornamented fish, the whitefish Coregonus lavaretus. In an experimental design in which nongenetic environmental effects were minimized, we found that highly ornamented females, males, and their parental combinations had offspring with better swimming performance and predator‐avoidance ability than less ornamented individuals or combinations. Furthermore, highly ornamented females had larger offspring that also had higher yolk volume than less ornamented individuals. Offspring swimming performance was not dependent on offspring size and was only weakly affected by yolk volume, which suggest that swimming performance and measured morphological traits are independent fitness measures. In conclusion, mutual ornamentation of whitefish may signal the quality of individuals in both sexes, which may indicate ongoing directional selection for these ornamental traits. However, offspring fitness traits were also dependent on parental combination, which suggests that genetic compatibility effects may weaken the directional selection and the indicator value of the ornamentation.

Predator-induced respiratory responses in juveniles of vendace Coregonus albula, whitefish C. lavaretus, perch Perca fluviatilis and roach Rutilus rutilus

Predator-induced respiratory responses of juvenile vendace, whitefish, perch and roach were studied in an intermittent-flow respirometer by creating visual contact between test fishes and predators (juvenile northern pike). Vendace and whitefish always responded to the presence of pike with increased oxygen consumption. The response of perch was the opposite: oxygen consumption decreased to near the standard respiratory level. Roach responded more variably: some individuals increased their oxygen uptake while others decreased it. Changes in the rate of respiration during exposure to predation are supposed to be caused by the differences in locomotory activity due to induced antipredator behaviour. According to their responses, these species could be grouped into escapers (coregonids), hiders (perch) or indeterminates (roach). The species-specific differences in the antipredator behaviour originate in morphological and physiological characteristics which together determine the effectiveness of a particular antipredator style (i.e. either hiding or escaping).

Consistency of standard metabolic rate in relation to life history strategy of juvenile Atlantic salmon Salmo salar

Temporal consistency of relative standard metabolic rate (rSMR) of individual Atlantic salmon Salmo salar juveniles in three stocks was investigated. The stocks differed in their geographical origin and natal habitat (fresh water, brackish water, seawater). Oxygen consumption measurements of hatchery-reared fish hatched in February 2005 were conducted three times: in early spring 2006, in autumn 2006, and in late spring 2007. The results partly disagreed and partly agreed with earlier studies, in which temporal consistency of SMR in juvenile salmonids have been addressed. In the first period from early spring to autumn, no correlation between rSMR statuses of individuals was found whereas in the second period from autumn to late spring, fish were mainly observed to maintain their relative SMR level indicating a significant repeatability of individual rSMR status over the latter period. Furthermore, a relationship between rSMR status and life history strategy was found: post-smolts and smolts had higher SMR than non-smolts.

Metabolic rate, growth and aggressiveness in three Atlantic salmon Salmo salar populations.

Standard metabolic rate (R(S)), specific growth rate (G) and aggressiveness were investigated in three Finnish populations of Atlantic salmon Salmo salar (Neva, Saimaa and Teno), which were reared in identical hatchery conditions. The populations differed in their geographical origin and native habitat. There was a significant difference between populations in R(S): the southernmost Neva population had higher values in R(S) than the northernmost Teno population. No difference was found in G or aggressiveness between the populations. G was found to have a significant positive association with aggressiveness and R(S) among the three populations, however, these results were not statistically significant after correction for multiple tests. There was no significant association between R(S) and aggressiveness. Higher metabolic rate of the most southern population Neva is suggested to be an adaptation to the more abundant food sources of the southern stream.

The information content of odour, colour and tactile cues in the mate choice of minnows

Sexual displays often involve many different signal components, which may give information about the same or different mate qualities. We studied the information content of different signals in male minnows (Phoxinus phoxinus) and tested whether females are able to discriminate between males when only olfactory cues are present. We found that females preferred the odour of males with a more saturated (i.e., redder) belly, but only when the females had been in physical contact with the males before the experiments. Instead, when unfamiliar males were used, females did not discriminate between male odours and also the overall swimming activity (mate choice intensity) of the females was significantly lower. More ornamented males had lower number of Philometra ovata parasites (indicated by belly saturation) and Neoechinorhynchus rutili parasites (indicated by belly hue) than their less ornamented counterparts. We did not find experimental evidence for female odour preference being linked to belly hue and breeding tubercle number, but in the nature these traits were associated with the condition factor of the males. Taken together, our results suggest that belly colouration and breeding tubercles give honest information on several aspects of male quality. In addition females may learn the association between male colouration and their olfactory signals and utilize this information when visual signals are not present.

Comparison of Smoltification in Atlantic Salmon (Salmo salar) from Anadromous and Landlocked Populations Under Common Garden Conditions

We compared smolt physiology of Atlantic salmon stocks, that migrate from freshwater stream environments to a freshwater lake (Lake Saimaa, Finland), from the Neva River (Russia) to the brackish water of the Baltic Sea, and from the Teno River (Finland/ Norway) to the full-strength seawater of the Arctic Ocean. The three fish stocks were reared under common garden conditions, and ion homeostasis, seawater tolerance, activities of gill and kidney Na,K-ATPase and [3H]ouabain binding of gill and kidney tissues were determined at different phases of smoltification. Activity of gill Na,K-ATPase and number of gill [3H]ouabain binding sites reached peak values in May and were strongly suppressed in July. Osmolality and Na+, Cl-, and Mg2+ ion concentrations of blood plasma decreased during smoltification. &agr;la and &agr;lb isoforms of gill Na,K-ATPase decreased and increased, respectively, during smoltification. Although small differences appeared at some points in time, the seasonal pattern and magnitude of changes in smolt characteristics were generally similar in the Saimaa salmon and in the anadromous stocks of the Neva and Teno salmon. It is suggested that the strong smoltification process of the landlocked Saimaa salmon is somehow necessary for migration of the young salmon from river to lake and therefore has been retained in evolution.

Penetration and Migration Success of Diplostomum spp. Cercariae in Arctic Charr

Abstract We exposed 2 groups of young-of-the-year Arctic charr (Salvelinus alpinus) singly to 54 ± 2 (mean ± SE) Diplostomum spp. cercariae that had emerged from 4 randomly sampled snail hosts (Lymnaea stagnalis). The rearing tanks of the fish received Diplostomum spp. cercariae via the incoming water; therefore, 18 of the 36 fish had parasites in their eyes before the experimental exposure. Of the Diplostomum spp. cercariae presented to the fish, 19% penetrated and 46% of those that had penetrated the fish migrated successfully to the lens of the fish eye. The migration success of Diplostomum spp. from the site of penetration to the fish eye lens was lower in the previously parasitized (37.0 ± 8.7% [mean ± SE] adjusted with the number of penetrated cercariae) than in the unparasitized fish (55.3 ± 8.8%) and differed between the individual snail host from which the cercariae had emerged. In addition, the migration success of Diplostomum spp. decreased with an increase in the number of the cercariae that penetrated the fish. At the individual snail host level, there seemed to be a trade-off between penetration and migration ability of the cercariae. The results indicate that success of Diplostomum spp. in penetration and especially in migration to the fish eye is affected by both the molluscan first intermediate host and the piscine second intermediate host.

Phenotypic plasticity in growth and fecundity induced by strong population fluctuations affects reproductive traits of female fish

Abstract Fish are known for their high phenotypic plasticity in life‐history traits in relation to environmental variability, and this is particularly pronounced among salmonids in the Northern Hemisphere. Resource limitation leads to trade‐offs in phenotypic plasticity between life‐history traits related to the reproduction, growth, and survival of individual fish, which have consequences for the age and size distributions of populations, as well as their dynamics and productivity. We studied the effect of plasticity in growth and fecundity of vendace females on their reproductive traits using a series of long‐term incubation experiments. The wild parental fish originated from four separate populations with markedly different densities, and hence naturally induced differences in their growth and fecundity. The energy allocation to somatic tissues and eggs prior to spawning served as a proxy for total resource availability to individual females, and its effects on offspring survival and growth were analyzed. Vendace females allocated a rather constant proportion of available energy to eggs (per body mass) despite different growth patterns depending on the total resources in the different lakes; investment into eggs thus dictated the share remaining for growth. The energy allocation to eggs per mass was higher in young than in old spawners and the egg size and the relative fecundity differed between them: Young females produced more and smaller eggs and larvae than old spawners. In contrast to earlier observations of salmonids, a shortage of maternal food resources did not increase offspring size and survival. Vendace females in sparse populations with ample resources and high growth produced larger eggs and larvae. Vendace accommodate strong population fluctuations by their high plasticity in growth and fecundity, which affect their offspring size and consequently their recruitment and productivity, and account for their persistence and resilience in the face of high fishing mortality.

A methodological approach to measuring the oxygen consumption profile of six freshwater fish species: implications for determination of the standard metabolic rate

Procedures for the determination of standard metabolic rate (SMR) are variable and subjective in respirometry. We examined the oxygen consumption profile of six fish species (three salmonids and three cyprinids) in respirometry, and analysed the implications for the determination of SMR. In addition, we used data on Arctic charr (Salvelinus alpinus) and bleak (Alburnus alburnus) to define, how the length of a measuring period affects the determination of SMR and to investigate the temporal consistency of SMR. Fish activity in the respirometer differed between the species and there was a family-specific response to change in illumination. In salmonids, switching off the lights resulted in an increased oxygen consumption rate for hours, whereas in cyprinids the response was shorter or totally absent. In Arctic charr and bleak, individual oxygen consumption profiles remained unchanged between the consecutive trials. The results emphasize the importance of taking species-specific responses into account when determining SMR.