Spawning characteristics of the anadromous brown trout in a small Swedish stream

The spawning pattern of the anadromous brown trout Salmo trutta was studied in Själsöån, a small stream in Gotland, Sweden, during eight winters between 1992–1993 and 1999–2000. The total length ( L _T) at spawning was normally distributed (185–890 mm) for females and multimodal for males (300, 400 and 550 mm most frequent length classes). Spawning males were significantly younger (2+ to 4+ years) than females (3+ to 5+ years). The sex‐ratio at the beginning and at the end of the spawning season favoured males. The mean ±  s . d . number of spawners was 70 ± 16 individuals per year. Migration into and out of the stream occurred between November and June. The highest number of spawning fish was found in the stream at the end of November or at the beginning of December. Migration mainly occurred during high water flow and at night. The majority of the females entered the stream and spawned the same (29·3% of all the females) or the next night (32·8% of all the females) while males may have stayed for 2 to 3 weeks (21·3% of all the males) in the stream before spawning. Males usually remained much longer in the stream (mean ±  s . d . 45 ± 56 days) than females (16 ± 30 days). Females lost more mass in the stream (mean ±  s . d . 17·3 ± 8·6%) than males (7·7 ± 9·6%). For both sexes, mass loss was positively correlated with the time spent in the stream. Only 7·3% of the males and 5·7% of the females occurred in the stream for >1 year. Spawning took place only during the night.     

Timing matters: species‐specific interactions between spawning time,substrate quality,and recruitment success in three salmonid species

Substratum quality and oxygen supply to the interstitial zone are crucial for the reproductive success of salmonid fishes. At present, degradation of spawning grounds due to fine sediment deposition and colmation are recognized as main factors for reproductive failure. In addition, changes in water temperatures due to climate change, damming, and cooling water inlets are predicted to reduce hatching success. We tested the hypothesis that the biological effects of habitat degradation depend strongly on the species‐specific spawning seasons and life‐history strategies (e.g., fall‐ vs. spring‐spawners, migratory vs. resident species) and assessed temperature as an important species‐specific factor for hatching success within river substratum. We studied the species‐specific differences in their responses to such disturbances using egg‐to‐fry survival of Danube Salmon (Hucho hucho), resident brown trout (Salmo trutta fario), and migratory brown trout (Salmo trutta lacustris) as biological endpoint. The egg incubation and hatching success of the salmonids and their dependence on temperature and stream substratum quality were compared. Hatching rates of Danube salmon were lower than of brown trout, probably due to higher oxygen demands and increased interstitial respiration in spring. Increases in maximum water temperature reduced hatching rates of resident and migratory brown trout (both fall‐spawners) but were positively correlated with hatching rates of Danube salmon (a spring‐spawner). Significantly longer incubation periods of resident and migratory brown trout coincided with relatively low stream substratum quality at the end of the egg incubation. Danube salmon seem to avoid low oxygen concentrations in the hyporheic zone by faster egg development favored by higher water temperatures. Consequently, the prediction of effects of temperature changes and altered stream substratum properties on gravel‐spawning fishes and biological communities should consider the observed species‐specific variances in life‐history strategies to increase conservation success.     

Dynamique de la population de Truite commune (Salmo trutta) d'un ruisseau breton (France): les géniteurs sédentaires

Population dynamics of brown trout (Salmo trutta) in a breton stream (France): The non-migrant spawners.The biological factors of the population dynamic of brown trout in a tributary of the Scorff river, have been studied during 4 years. The characteristics of the spawners, present in the stream before the spawning migration from the main river, are described. These spawners were born in the stream and stayed there during their entire life-span. Among mature fish the sex ratio was always in favour of males. During the third and the fourth years of life, annual mortality rate was 70% for males and 50% for females. 1+ spawners were these which had the best 0+ growth rate. A majority of males first matured at 1+ years of age. On an average, 1+ females were responsible for 25% of the total reproductive potential. The number of 3+ and 4+ females seemed to depend on the fishing effort.

     

Life-history effects of migratory costs in anadromous brown trout

Mean size of sexually mature anadromous brown trout (sea trout) Salmo trutta in south-east Norway increased significantly with migratory distance ( D ) between the feeding area at sea and the spawning area in fresh water, from 32 cm for those spawning close to the river mouth to 43 cm at the spawning grounds 40 km inland. This was largely due to an increased size of the smallest anadromous spawners with increasing D . The raised mean size of the long-distance migrants is paralleled by an increased age at sexual maturity. Body mass at the same length of sea trout decreased with D in fresh water, meaning that the fish moving far inland was slimmer than those spawning near the coast. Gonadal mass of first-time spawning anadromous males declined significantly with D , and the fecundity and the ratio of fecundity over mean mass of the individual eggs adjusted for variation in fish mass, increased with D . There was no clear relationship between the ratio of anadromous to resident fish and D , probably because more variables than D , influence this relationship in the study streams.     

The growth of charr, Salvelinus willughbii Günther, in Windermere

The growth of charr ( Salvelinus willughbii Günther ) caught in Windermere from 1941–1952 has been studied. Scales were used for determination of age and back-calculation of length for age. Autumn and spring spawners, males and females, and charr of normal and dwarf growth were treated separately. In fish of normal growth, the spring spawners were significantly smaller than the autumn spawners at ages 1 and 2 years, and significantly larger from age 4 years onwards. There was little difference in growth between males and females within the two spawning populations. Charr of lengths of less than 200 mm at age 4 years were considered to be dwarfs. Mean lengths at capture of male charr were: autumn spawners normal growth 272 mm, dwarf 218 mm; spring spawners normal growth 327 mm, dwarf 194 mm. The oldest recorded age was 8 years.     

Lack of species-specific primer effects of odours from female Atlantic salmon, Salmo salar, and brown trout, Salmo trutta

We exposed, in two successive spawning seasons, individually placed precocious male Atlantic salmon ( Salmo salar ) and brown trout ( Salmo trutta ) parr to odour stimuli (ovarian fluid and urine mix) from ovulated conspecific or heterospecific anadromous females. Atlantic salmon parr had significantly higher plasma concentrations of the hormones 17α,20β-dihydroxy-4-pregnen-3-one (17,20β-P), 11-ketotestosterone (11-KT) and testosterone (T) after exposure to odours from conspecific females or from brown trout females compared to parr exposed to a control solution (0.9% NaCl). We did not observe any significant differences between the hormone levels in salmon parr exposed to the two female odours. The salmon parr exposed to conspecific odours had significantly higher volumes of strippable milt compared to the controls, but we did not find any significant differences when comparing the effect of the two female odours. Brown trout parr had significantly higher plasma 17,20β-P levels following exposure to heterospecific female odours compared to control males, but there was no significant difference between males exposed to the different female odours. We did not observe any significant differences in plasma levels of T and 11-KT and in milt volumes between exposed and control trout. Taken together, the results from both tested species indicate that the potency of heterospecific stimuli in stimulating increased plasma sex steroid hormone levels in male parr was as strong as stimuli from conspecific females. The results are discussed in connection to observed hybridisation between the two sympatric species.     

Spatial association of nest construction by brown trout Salmo trutta

Spawning patterns in female brown trout Salmo trutta were examined by documenting the construction of nests in a small stream and later excavating them to recover progeny. The maternal provenance of nests was determined by genetic typing of embryos using microsatellite markers. Seventy-two nests, for which position and date of construction were known, were made by 59 individuals. Position and date of construction were known for a further 35 nests, comprising 11 Atlantic salmon Salmo salar nests and 24 nests which contained few or no progeny. Salmo trutta showed a behavioural preference for spawning near (≤ 1 m) prior nests; nests made by different individuals tended to accumulate in a spatial sequence that progressed upstream. The directionality of the association between prior and new nests suggests that later spawners use the residual depressions created by previous spawners as the first element of their own nests.     

Use of space and food by resident and migrant brown trout,Salmo trutta

Synopsis Parr and resident forms of brown trout,Salmo trutta, from Vangsvatnet Lake, Norway live in freshwater, while migrant forms live in coastal waters during summer and in freshwater during winter. About 80% of parr and residents live at depths <5 m, smolts and migrants are more confined to near-surface water. Brown trout partly segregate by size, age and sex from spring through autumn. More than 90% of parr and residents in the tributaries are 0–2 years old, 2–14 cm in length, in the littoral zone 0–3 years old, 7–24 cm in length, and in the pelagic zone 2–6 years old, 18–32 cm in length. The mean body length of equal-aged fish increases from tributaries through littoral to pelagic zones in the lake. Smolts (2–7 years, 14–29 cm) leave the lake from April through August and return during September–October. Migrants (2–11 years, 23–67 cm) leave the take in April–May and return during August–September; sexually mature fish return earlier than immatures. Female brown trout are less stream-dwelling, but more migrant and pelagic than males. Most individuals in the lake population spend the winter in the littoral zone. In the tributaries, diet differs significantly between age-groups of parr; young fish feed on smaller food items than do older fish. In the lake, parr and residents living in the same habitats feed on the same food items. Littoral brown trout feed mainly on insect larvae and chironomid pupae, pelagic brown trout feed on zooplankton and surface insects. Migrants feed little while staying in freshwater, except for matures which feed on young salmonids and surface arthropods during the 2 first months after they had returned from coastal waters. The results are discussed in relation to growth possibilities and mortality risks of the different habitats.Reprint request to B. Jonsson.     

Ecological Forms of Black Sea Brown Trout (<Emphasis Type="Italic">Salmo trutta labrax</Emphasis>) in the Mzymta River as Manifestation of Ontogenetic Plasticity

Populations of brown trout in the Mzymta River and its tributaries include anadromous (mainly female) and resident (mainly males) fish. Some resident males in the basin of the Mzymty River attain sexual maturity at the age 1+, and resident females mature at the age 2+ or 3+. The maximum age of resident fish is 4+ in the samples studied. Migrations of anadromous brown trout to the sea occur at the ages 1+, 2+, or 3+. Future spawners spend from 1 to 4 years at feeding grounds in the sea. Smolts of the population are characterized by performing not only spring but also autumn migrations to the sea. One smolt specimen has been detected upstream from the dam in the river where spawners of anadromous brown trout do not migrate; this means that the capability for sea migrations persists long in the population represented only by resident specimens of brown trout. The diversity of life cycles and ecological forms in populations of brown trout is not lower than in populations of brown trout in Northern and Western Europe. The comparison of the data obtained with published data makes it possible to come to the conclusion about the high plasticity of ontogenesis of Black Sea brown trout.     

Characteristics of the spawning migrations of brown trout, Salmo trutta L., and rainbow trout, S. gairdneri Richardson, in Great Lake, Tasmania

Upstream spawning migrations of mature brown trout, S. trutta , and rainbow trout, S. gairdneri , were studied in Liawenee Canal, Great Lake from 1949 to 1985. Brown trout migrations normally occurred from early April to mid-May and rainbow trout from late August to early November. In 1983, 16 425 brown trout and 1338 rainbow trout passed through a fixed upstream diversion trap. Brown trout spawning migrations occurred predominantly over the temperature range 6–10° C, while rainbow trout migrated predominantly over the range 5–11° C. Migrations peaked at water temperatures of 7.6°C (males) and 7.8°C (females) for brown trout, and 8.3°C (males) and 9.6°C (females) for rainbow trout. Rainbow trout migrations occurred at high flow conditions and were positively correlated with canal flow increases, while brown trout migrated under low canal flow. Mean length, weight and condition of rainbow trout of both sexes decreased significantly during migrations. Female brown trout decreased in weight and condition but not in length; male brown trout did not change in condition despite decreases in both length and weight during migrations. Overall sex ratio was 2:1 (female:male) for both species, with the relative proportion of male fish decreasing as migrations progressed. Age composition changed during migrations; dominant age classes were 3 < 4 < 5 + years for both species. Comparison of length, weight, condition and age revealed minor changes during the 37-year period 1949–1985.     

Partial migration in a landlocked brown trout population

Population densities of landlocked lake‐migratory brown trout Salmo trutta were estimated in two distinct lotic sections, separated by a lentic segment, in the Greåna River, Sweden, and individual growth and habitat use were monitored for 835 tagged brown trout from September 1998 to June 2000. Residency dominated in the upstream section where density of 0+ and 1+ year brown trout was low and growth rate high. In contrast, >90% of the brown trout that migrated to the lake originated from the downstream section, where density was high and growth rate low. For ≥2+ year individuals, growth rate was similar between the two stream sections, but densities were higher in the upstream than in the downstream section. Lake‐migrants had higher growth rates than non‐migrants (residents) during the autumn of both years. From September to May, migrants increased their body mass by >35%, whereas non‐migrants increased by <5%. Approximately 70% of the brown trout moved <10 m and <2% moved between the two stream sections, indicating that the lentic habitat might function as a barrier for juveniles. Differences in migratory behaviour, density and growth between the upstream and the downstream section might indicate that environmental factors influence the decision to migrate. It cannot be excluded, however, that the observed differences are genetically programmed, selected by migration costs that favour migratory behaviour downstream and residency upstream.     

Reproductive biology of the threatened golden galaxias Galaxias auratus Johnston and the influence of lake hydrology

Golden galaxias Galaxias auratus (31–235 mm fork length, L _F) were collected monthly from littoral habitats in Lakes Crescent and Sorell, Tasmania, Australia, between July 2000 and December 2002. Spawning habitats were identified and monitored in both lakes, and surveyed in Lake Crescent. Trends in gonado-somatic indices and reproductive stages of development indicated that gonad development in both sexes begins in midsummer and peaks in late autumn to early winter. Males mature at smaller sizes (50% at 52 mm L _F) than females (50% at 76 mm L _F), larger individuals are predominately females (95% of fish ≥138 mm L _F), and overall male to female ratios are female biased ( c . 1:2). Spawning occurs late autumn to early spring (water temperatures = 1·4–9·7° C) with peaks in spawning activity in winter (mean water temperatures <5° C). Demersal adhesive eggs ( c. 1·5 mm diameter) were found on cobble substrata ( c. 20–250 mm diameter) in littoral areas ( c. 0·2–0·6 m deep) and fecundity of fish 71–181 mm L _F ranged from 619 to 14 478 eggs. The rate of change in water level over the 20 days prior to monthly sampling was important in explaining the occurrence of spent fish and this accounted for temporal differences in spawning between the populations. Lake hydrology influences the reproductive cycle of G. auratus by possibly providing a stimulus for spawning and it controls the availability of spawning habitat in Lake Crescent. Seasonal hydrological cycles ( i.e. rises during late autumn to winter) and a minimum water level of 802·20 m Australian Height Datum in Lake Crescent during autumn (above which littoral areas of cobble substratum are inundated) are critical to G. auratus populations.     

Brown trout (<Emphasis Type="Italic">Salmo trutta</Emphasis>) invasiveness: plasticity in life-history is more important than genetic variability

Brown trout of German origin were introduced into Patagonian National Parks in 1905, where they acclimatized and underwent population expansion endangering populations of native species like Galaxiidae. Spawning adults of two populations were sampled in 2004. Their age, length-at-age and migratory behaviour were assessed from scale samples, as well as their variation at the coding LDH-C1* and eight non coding microsatellite loci. Between-population differentiation for life history (spawning time, migratory behaviour, length and weight at age) and reduced genetic variation were revealed. Based on genetic variation, effective population size smaller than 50 individuals has been estimated for the founder stock, and its German origin has been genetically traced. Flexibility in migratory behaviour and spawning time were identified as key factors conferring competitive advantage on those brown trout populations.     

Body composition and energy allocation in life-history stages of brown trout

Energy contents of immature parr and smolts, and mature resident and anadromous brown trout Salmo trutta sampled from a small stream in southern Norway were estimated from lipid, protein and carbohydrate concentrations. In immatures the lipid concentrations were highest in parr in the autumn. Mean lipid concentrations increased significantly with age in parr sampled in autumn (1·3% in age 0+ to 3·4% in age 3+), whereas they did not in smolts. The lipid concentrations of parr in spring were not significantly different from those of similarly aged smolts. By contrast, the relative water content (%) decreased with age in parr in the autumn and increased with age in smolts, mean values being slightly higher in smolts (78%) than in parr (77%). Protein and carbohydrate concentrations did not vary with age in the immature fish, mean protein concentrations being 18·0, 17·5 and 16·8% in parr in the autumn and spring, and in smolts, respectively. In residents, the concentrations of lipids were lower and of water higher, in age group 1 than in older fish, whereas there was no significant variation with age amongst anadromous trout. The energy concentration of 2+ smolts (349 kJ 100 g^-1) was similar to that of 0+ parr in the autumn. Mean somatic energy density in autumn was 1·1 times higher in freshwater residents than in parr at age 1+ (407 and 387 kJ 100 g^-1) and marginally different at age 2+ (462 and 426 kJ 100 g^-1, respectively). The energy contents per unit mass of residents were 1·3–1·6 times that of similar aged smolts. Mean somatic energy density of anadromous trout (504 kJ 100 g^-1) was higher than that of residents (455 kJ 100 g^-1). Somatic energy, lipid and protein concentrations were correlated highly with water contents of all life stages, age and sex groups.     

Sex steroids,gonadal histology and biological indices of fall and spring Caspian lamprey (<Emphasis Type="Italic">Caspiomyzon wagneri</Emphasis>) spawning migrants in the Shirud River,Southern Caspian Sea

This study investigates sex steroids, gonadal histology and some biological indices of fall and spring spawning migrants of Caspian lamprey Caspiomyzon wagneri (Kessler, 1870). Blood and gonad samples were collected from 15 migrants during fall and spring. Serum sex steroid levels including testosterone (T), 17β-estradiol (E₂) and progesterone (P) were determined with ELISA and gonadal development was studied using conventional histological methods. Our results showed serum E₂ level in females were similar in the two seasons but in males, fall migrants had higher serum E₂ concentrations. No differences were found in T levels in fall and spring migrants. Serum P concentration in fall migrant males were significantly higher than spring migrant males while spring migrant females had higher serum P levels compare to fall migrant females. Gonads in both fall and spring migrants were in the final stage of maturity. Fall and spring migrant males had similar HSI and GSI; fall migratory female had significantly higher HSI and GSI. Sex ratios were close to 1:1 in both seasons. There was a significant relationship between fecundity and length in both seasons. Comparison of fecundity and egg diameter between fall and spring seasons showed no significant difference. These results indicate that both fall and spring migrants Caspian lamprey were ready for spawning. Further studies are needed to clarify when spawning occurs in Caspian lamprey.     

Spawning characteristics of brown trout and sea trout Salmo trutta L. in Kirk Burn, River Tweed, Scotland

The upstream spawning migrations of brown trout and sea trout were studied using stationary traps placed in Kirk Burn, a tributary of the upper Tweed. The sea trout spawning period extended from early November to the first week of December, while that of brown trout occurred from the middle of October to the third week of December. Sea trout were predominantly maiden spawners of ages 2.1+ and 3.1+ while brown trout were mostly age 2+ and 3+. Male-female sex ratios approximated 1:1.4 in sea trout but 6 : 1 in brown trout. Brown trout males participated in the spawning activities of sea trout. Low water conditions in Kirk Burn hindered the upstream movement of spawning sea trout, while sudden increases in water level appeared to stimulate the upstream migration of both brown trout and sea trout. The suggestion is advanced that the freshwater resident brown trout of the Tweed which migrate upstream into the smaller tributaries to spawn is wholly, or at least partially, the progeny of anadromous parents.     

Spawning success in Atlantic salmon (Salmo salar L.): a long-term DNA profiling-based study conducted in a natural stream

Spawning success of Atlantic salmon (Salmo salar L.) was investigated, under near-natural conditions, in the Girnock Burn, an 8-km long tributary of the River Dee in Scotland. Employing minisatellite-based DNA profiling, mating outcomes were resolved over three spawning seasons by assigning parentage to progeny samples removed from spawning nests ('redds'). While individual spawning patterns differed markedly, consistent trends were present over the 3 years studied. Multiple spawning was found to be prevalent. More than 50% of anadromous spawners of both sexes contributed to more than one redd. Up to six redds for a single female and seven for a single male were detected. Both sexes ranged extensively. Distance between redds involving the same parent varied from a few metres to > 5 km. Distances > 1 km were common. Both males and females ranged to a similar extent. Range limit was not correlated to fish size. Pairs were not monogamous, both males and females mating with different partners at different sites. Size assortative mating was apparent among 1991 spawners but was not detected for 1992 or 1995. Redd superimposition was found to be common (17-22% of redds over the 3 years), although it was not correlated to the number of anadromous spawners present. High levels of nonanadromous mature parr mating success (40-50% of total progeny sampled) were recorded, and these likely contribute greatly to the effective population size. The relevance of these findings at the individual and population level is discussed, with particular reference to management implications.     

High mortality in introduced brown trout depressed potential gene flow to a wild population

Hatchery reared 0+ year brown trout Salmo trutta , with 51 mm mean L _T, were released in a sea trout stream in June 1991 to compare the survival of wild and introduced trout during the freshwater stage from age 0+ to 2+ years. The introduced brown trout were homozygous for a genetic marker, enabling released individuals and their offspring to be distinguished phenotypically from the local sea trout. The mean size of 0+ and 1+ year introduced parr was larger than 0+ and 1+ year wild parr, while 2+ year parr of both groups were of the same size. Half year survival rates of both introduced and wild parr increased with size up to c . 80 mm (1+ years), but then decreased, and could be described by a polynomial regression function, with the same shape for both groups. The introduced parr had, however, a significant lower survival rate than the wild parr. The number of the introduced cohort decreased from 2200 at release in 1991 to c . 20 in March 1994 ( c . 1% of the original number). Between 1994 and 2000 no introduced individuals or offspring have been observed in the study area. High mortality at the parr stage and additional mortality until the spawning, give a low probability for a genetic impact on the local population as long as releases are restricted, both in time and number of fish.     

Incidence of physical injury of mature male parr in a natural population of brown trout

In a brown trout Salmo trutta population, there was a much higher frequency of injuries among mature male parr than among immature or female parr. The quantitative data are discussed in relation to spawning success and overall fitness.     

The influence of sex and spawning on levels of tryptophan, serotonin and 5-hydroxyindoleacetic acid in the brains of wild brook trout, Salvelinus fontinalis

Levels of tryptophan (TP), serotonin (5-hydroxytryptamine, 5HT) and 5-hydroxyindoleacetic acid (5HIAA) have been determined in the brains of wild brook trout, Salvelinus fontinalis (Mitchill), and brown trout, Salmo trutta L., using high performance liquid chromatography with electrochemical detection. Immediately prior to spawning, adult female brook trout exhibit higher levels of 5HT in the brain than adult males, immature brook trout and immature brown trout. After spawning, the highest levels of TP are found in spent males, which also have higher levels of 5HT in the brain than spent females and immature brook trout. Immature brook trout exhibit higher levels of 5HIAA than prespawning adults. This difference disappears after the spawning season. Serum protein levels and condition factors are lower in spent female brook trout; however, haematocrit values for both sexes remain unchanged after spawning.