Mature Parr Research Articles

Paternal Reproductive Strategy Influences Metabolic Capacities and Muscle Development of Atlantic Salmon (Salmo salar L.) Embryos

Male Atlantic salmon follow a conditional strategy, becoming either "combatants" that undertake a seaward migration and spend at least a year at sea or "sneakers" that remain in freshwater and mature as parr. A variety of physiological indices showed significant but small differences between the offspring of males that use these two reproductive tactics. Offspring fathered by anadromous male Atlantic salmon (Salmo salar L.) showed greater muscular development and muscle metabolic capacities but lower spontaneous movements than those fathered by mature male parr. At hatch and at maximum attainable wet weight (MAWW), offspring fathered by anadromous males had higher activities of mitochondrial (cytochrome C oxidase and citrate synthase) and glycolytic (lactate dehydrogenase [LDH]) enzymes than progeny of mature male parr. Enzymatic profiles of progeny of anadromous fathers also suggested greater nitrogen excretion capacity (glutamate dehydrogenase) and increased muscular development (creatine kinase and LDH) than in the progeny of mature parr. At MAWW, juveniles fathered by mature parr made considerably more spontaneous movements, presumably increasing their energy expenditures. For juveniles fathered by anadromous males, total cross-sectional areas of white and red muscle at hatch were higher due to the greater number of large-diameter fibers. We suggest that the slightly lower metabolic capacities and muscular development of alevins fathered by mature parr could reflect differences in energy partitioning during their dependence on vitellus. Greater spontaneous movements of offspring of mature male parr could favor feeding and growth after the resorption of the vitellus.

Social interactions between mature and immature parr of Atlantic salmon (Salmo salar) coexisting in artificial stream tanks

Social interactions between mature and immature parr of Atlantic salmon (Salmo salar) coexisting in artificial stream tanks

Population specific smolt development, migration and maturity schedules in Atlantic salmon in a natural river environment

Identifying differences in quantitative life history traits between cultured and native or non-native wild populations is important in assessing the impact of accidental and deliberate introductions of hatchery-reared fish into the wild. As the ability to exploit the marine environment is the defining life history characteristic of anadromous salmonids, knowledge of variation in smoltification characteristics among populations is crucial in determining how these introductions affect fitness in recipient populations. Data are presented here describing the timing and extent of the autumn migration; the propensity for male parr maturation; the timing of the spring migration; and the size of autumn and spring migrants from Atlantic salmon (Salmo salar) populations from various genetic backgrounds. These experiments were carried out under common garden conditions over a decade in the Srahrevagh River in the west of Ireland. Population specific genetically determined differences in quantitative life history traits associated with smoltification were apparent. These differences may reflect smolt quality and therefore impact on marine survival and ultimately lifetime fitness. Both hatchery domestication and geography (different selective environments) were found to be important factors determining smolt phenotypes, although it was difficult to measure the relative contribution of each. These results indicate that farm, native hatchery, non-native wild salmon (even from a neighbouring catchment) and their hybrids with native wild fish, are likely to produce less well adapted and thus poorer quality smolts than native wild populations and, where wild populations are extant, such stocks should not be used for enhancement purposes.

Reproductive strategies in small populations: using Atlantic salmon as a case study

Abstract – Wild salmonid populations with only a few breeding adults may not exhibit a significant reduction in genetic variability compared with larger populations. Such an observation suggests that effective population sizes are larger than population size estimates based on direct adult counts and/or the mating strategy maximises outbreeding, contributing to increased heterozygosity. In the case of wild Atlantic salmon Salmo salar populations, stratification by age classes and sexes on the spawning grounds avoids inbreeding and increases genetic variability. We studied the breeding composition of four Spanish salmon populations. Over a 7‐year period we concluded that the probability of within‐cohort mating is very low: females generally reproduce after two sea‐winters whereas males reproduce mostly as one sea‐winter (grilse) and/or mature parr. Considering different levels of contribution of mature parr to spawning derived from field surveys, we developed a simple model for estimating effective population sizes and found that they doubled with 65% parr contribution expected for rivers at this latitude (43°N), and ranged from 100–800 individuals. The effect of between‐cohort mating was modelled considering different ranges of differences in allele frequencies between cohorts and resulted in 28–50% increases in heterozygosity when considering a 65% parr contribution. The complex mating strategy of Atlantic salmon contributes to explain the high levels of genetic variability found for small populations of this species. This model can probably be extended to other animal species with mating strategies involving different cohorts.

A decrease in photoperiod shortly after first feeding influences the development of Atlantic salmon ( Salmo salar)

Four groups of Atlantic salmon fry ( n = 2000) were exposed to continuous light (LD24 : 0) from first feeding on 18th April 2001, after which they were exposed to either an 8 or 12 week period of short days (LD10 : 14) starting on either the 21st May or the 18th June. Each group was then returned to LD24 : 0 until the conclusion of the experiment the following March. In August 200 fish per treatment were individually PIT tagged. All groups were maintained under an ambient temperature regime. The highest levels of sexual maturation in 0+ male parr were recorded in the 12 week/May group (> 11% of the entire male and female population), with the lowest levels (< 1%) in the 12 week/June treatment and intermediate levels (> 6%) in the 8 week/May and 8 week/June groups ( P < 0.05). Between mid August and late October mature parr were heavier than their immature counterparts, but subsequently both cohorts maintained similar sizes. Fish showing signs of silvering were found from mid October onwards. However, it was only in the 12 week/June group that silvered fish had a significantly reduced condition factor and an increased gill Na +, K +-ATPase activity, indicative of smoltification. At the conclusion of the experiment, fish showing signs of silvering were most prevalent (30%) in the 12 week/June group. It is concluded that the initiation of maturation can be influenced by an 8 or 12 week period of short days (LD10 : 14) applied from mid May or mid June in the first growing season. The duration and timing of a stimulatory short day photoperiod during early development may also influence whether a fish undergoes smoltification in the coming year or whether it delays the parr–smolt transformation for at least a further year.

Reproductive Strategies Explain Genetic Diversity in Atlantic Salmon, Salmo salar

We investigated the relationship between conservation status and genetic variability in European and North American Atlantic salmon, Salmo salar, populations, many of which have suffered severe bottlenecks. A negative north--south cline exists for the status of population conservation in this species. A literature review of genetic variability and demographic parameters of wild Atlantic salmon populations resulted in no statistical associations between population conservation status and genetic variation at enzyme or VNTR loci. We found however, a negative relationship between male parr maturation rates and geographical latitude for both American and European populations. The increase in effective population size due to participation by mature male parr and the increased proportions of these males in smaller (southern) populations could explain the lack of expected relationship between genetic variation and conservation status.

The effect of temperature on growth and early maturation in a wild population of Atlantic salmon parr

Atlantic salmon Salmo salar parr exposed to heated water effluent were larger than parr living upstream of the discharge. There was no effect, however, of temperature on the incidence of male parr maturation, despite the link between growth and maturation found in other studies. Mature parr upstream of the effluent were smaller than mature parr downstream of it, suggesting a higher size threshold for maturation in those parr exposed to the heated water. The small distance between upstream and downstream sampling sites probably precluded genetic differences between the parr, thus implying an environmental influence on the threshold size above which male parr matured.

Small anadromous Salvelinus malma at the southern limits of its distribution

Anadromy in the Dolly Varden Salvelinus malma at the southern limits of its distribution were examined by an intensive field survey and measurements of otolith Sr and Ca concentrations. Body sizes of anadromous individuals were small, only slightly larger than those of mature parr, and the degree of anadromy was extremely low.

Differential lifetime success and performance of native and non‐native Atlantic salmon examined under communal natural conditions

The lifetime success and performance characteristics of communally reared offspring of wild native Burrishoole (native), ranched native (ranched) and non‐native (non‐native) Atlantic salmon Salmo salar from the adjacent Owenmore River were compared. Non‐native 0+ year parr showed a substantial downstream migration, which was not shown by native and ranched parr. This appears to have been an active migration rather than competitive displacement and may reflect an adaptation to environmental or physiographic conditions within the Owenmore River catchment where the main nursery habitat is downstream of the spawning area. There were no differences between native and ranched in smolt output or adult return. Both of these measures, however, were significantly lower for the non‐native group. A greater proportion of the non‐native Atlantic salmon was taken in the coastal drift nets compared to the return to the Burrishoole system, probably as a result of the greater size of the non‐native fish. The overall lifetime success of the non‐native group, from fertilized egg to returning adult, was some 35% of native and ranched. The ranched group showed a significantly greater male parr maturity, a greater proportion of 1+ year smolts, and differences in sex ratio and timing of freshwater entry of returning adults compared to native, which may have fitness implications under specific conditions.

Altitudinal variation in the relationship between growth and maturation rate in salmon parr

Summary It is well established that the likelihood of an individual animal becoming mature is influenced strongly by its previous growth. However, with few exceptions, it is not known whether common relationships between the two parameters apply within and among populations. Using data collected from tributaries of a single river, we investigate the relationship between size and maturation in Atlantic salmon parr, and whether spatial variation in the incidence of parr maturation can be explained by variation in growth rates. There was spatial variation in the size of parr, a large proportion of which was attributable to altitude. However, this did not explain the variation between sites in the maturation rate of parr. In contrast to earlier findings, there was no relationship between the mean size of parr at a site and the percentage of males that matured there for the age class in which most mature males were found. Within a site size at age was a good predictor of maturation, but across sites this relationship was modified by altitude. For a given age and size a parr was more likely to become sexually mature if it came from a high‐altitude site. Spatial variation in the incidence of male parr maturity is not simply the result of variation in growth rates. The size threshold above which parr male parr matured depended on altitude, which could serve as a proxy for growth opportunity. We suggest adaptive explanations for variation in the relationship between growth and maturation, particularly the importance of relative, as opposed to absolute body size. Our study suggests a high level of complexity in the proximate mechanisms governing life‐history strategies in order to bring about adaptive strategy choice.

Winter growth and survival of juvenile Atlantic salmon (Salmo salar) in experimental raceways

We used experimental raceways to determine overwinter mortality of wild-reared immature and mature post-young-of-the-year Atlantic salmon (Salmo salar). Secondarily, we investigated the effects of differing treatments (velocity and shelter) on winter growth and survival. Overall survival from November to April was 94%, and survival of immature (98%) and mature (90%) parr, although statistically different, was very similar. Immature parr grew more in length than mature parr, and both immature and mature parr in higher velocity (12 cm·s–1) raceways grew more than those in lower velocity (0.6 cm·s–1) raceways. Stomach contents were twofold greater in parr occupying higher velocity raceways than those in lower velocity raceways. Caloric content of immature and mature parr did not differ in any of five monthly samples. Lowest caloric content occurred in early February and increased between February and March when water temperatures were well below those considered optimal for growth. Although ice cover was present, isolating parr from conditions that occur in natural settings may have helped parr achieve nearly 2.5 times greater survival than parr in the wild. Further, whereas previous studies showed parr select habitats to minimize energetic loss, our results show a distinct advantage for parr to expend energy to feed during winter.

Long-term consequences of variation in timing and manner of fry introduction on juvenile Atlantic salmon (Salmo salar) growth, survival, and life-history expression

We tested the influence of introduction time and the manner of introduction on growth, survival, and life-history expression of Atlantic salmon (Salmo salar). Introduction treatments included three fry stocking times and stream rearing of embryos. Despite poor growth conditions during the early stocking period, early-stocked fish were larger throughout the entire study period, likely the result of prior residence advantage. This interpretation was reinforced by the laboratory study, where early-stocked fish outgrew late-stocked fish when reared together, but not when they were reared separately. In contrast to growth, abundance of stocked fish was greatest for fish stocked during the middle period, and this stocking group produced the greatest number of smolts. Despite smaller size, survival of stream-incubated fish was generally greater than survival of stocked fish. Introduction timing had a pronounced effect on smolt age but a weak effect on extent of parr maturation. Overall, these observations indicate that small differences (~2 weeks) in introduction time can have long-term effects on size, survival, and life-history expression. Results suggest stabilizing selection on introduction times, mediated by the interaction between prior residence (advantage to fish introduced earlier) and habitat suitability (advantage to fish introduced later).

Life history dependent morphometric variation in stream-dwelling Atlantic salmon.

The time course of morphometric variation among life histories for stream-dwelling Atlantic salmon ( Salmo salar L.) parr (age-0+ to age-2+) was analyzed. Possible life histories were combinations of parr maturity status in the autumn (mature or immature) and age at outmigration (smolt at age-2+ or later age). Actual life histories expressed with enough fish for analysis in the 1997 cohort were immature/age-2+ smolt, mature/age-2+smolt, and mature/age-2+ non-smolt. Tagged fish were assigned to one of the three life histories and digital pictures from the field were analyzed using landmark-based geometric morphometrics. Results indicated that successful grouping of fish according to life history varied with fish age, but that fish could be grouped before the actual expression of the life histories. By March (age-1+), fish were successfully grouped using a descriptive discriminant function and successful assignment ranged from 84 to 97% for the remainder of stream residence. A jackknife of the discriminant function revealed an average life history prediction success of 67% from age-1+ summer to smolting. Low sample numbers for one of the life histories may have limited prediction success. A MANOVA on the shape descriptors (relative warps) also indicated significant differences in shape among life histories from age-1+ summer through to smolting. Across all samples, shape varied significantly with size. Within samples, shape did not vary significantly with size for samples from December (age-0+) to May (age-1+). During the age-1+ summer however, shape varied significantly with size, but the relationship between shape and size was not different among life histories. In the autumn (age-1+) and winter (age-2+), life history differences explained a significant portion of the change in shape with size. Life history dependent morphometric variation may be useful to indicate the timing of early expressions of life history variation and as a tool to explore temporal and spatial variation in life history expression.

Energy allocation among developmental stages, age groups, and types of Atlantic salmon (Salmo salar) spawners

Relationships between energy density (kJ·100 g–1) and body length (mm), which varied between life-history stages of Atlantic salmon (Salmo salar), were described by power functions. The variation was chiefly caused by differences in lipid concentrations. Energy densities of maturing and rematuring parr were higher than those of similarly aged smolts. Monthly specific growth rate was higher in maturing parr than in salmon at sea. Mature parr males allocated relatively more energy to gonadal development and less to soma development than anadromous males. Spawning expenditure increased from 34 to 53% for 55- to 72-cm-long females. In males, similar losses were from 47 to 49% of their total energy content at river entry. More energy was used in reproduction in a long river than in a short one. Male allocation to gonads relative to soma was highest in the shorter river. Energy allocation pattern varied among developmental stages. Very energy-rich male parr rematured in subsequent years without going to sea; less energy-rich ones smolted and migrated to sea.

Photoperiodic effects on precocious maturation, growth and smoltification in Atlantic salmon, Salmo salar

Abstract Current Atlantic salmon farming practice induces early smoltification with artificial photoperiod regimes, however the importance of these photoperiods on parr maturation and interactions with smoltification are poorly understood. These questions were addressed in the present investigation, which examined the effects of photoperiod manipulation on the development, maturation and smoltification of individually tagged parr. Approximately 9000 salmon parr from a high grilsing stock were exposed to continuous light (LL) from first feeding. Three sub-groups of 2400 parr, each sub-group in triplicate tanks, were then exposed to an 8-week “winter photoperiod” (LD 10:14) starting on either the 18th May, the 9th August or the 20th September (defined, respectively, as the May, August and September groups). Following the artificial winter, each group was returned to LL. A fourth group of 1600 fish was maintained in replicate tanks on LL throughout. The highest levels of maturation (approx. 20%) were recorded in the May group. August and September groups showed low levels of maturity ( It is concluded that the photoperiod to which parr are exposed early in their life acts as an important trigger for precocious maturation but does not necessarily phase shift the endogenous rhythm which is thought to control its timing. Smoltification is strongly influenced by the timing of exposure to winter photoperiod with clear evidence indicating that maturation and smoltification are not mutually exclusive processes.

Individual growth and phase differentiation of lacustrine masu salmon, Oncorhynchus masou, under artificial rearing conditions

In lacustrine masu salmon, Oncorhynchus masou, originated from anadromous fish and inhabiting an artificial lake (Shumarinai Lake), we examined the relationship between individual growth during the juvenile stage and phase differentiation under artificial rearing conditions. In females, the mean fork length of potential (subsequent) 1+ smolts and potential 1+ parr (1+ parr show fish that neither smolted nor matured until 1+ autumn) always differed after their first summer (0+ summer), the former being larger. In males, the juveniles that grew faster during their first spring became 0+ mature male parr. After their first summer, potential 1+ smolts were always larger in body length than potential 1+ mature parr and potential 1+ parr. These results were similar to previous reports of anadromous masu salmon, suggesting that the lacustrine masu salmon studied seems to have maintained the phase differentiation as in the original fish, likely because only 60 years have passed since the formation of the lacustrine population.

Differential energy allocation of alternative male tactics in masu salmon (Oncorhynchus masou)

To compare energy allocation to gonad, relative to soma, between alternative male tactics (mature parr and migratory males) in masu salmon (Oncorhynchus masou), we quantified energy contents in somatic and testicular tissues for the two tactics from two lake-run populations (Shikaribetsu Lake and Shumarinai Reservoir) in Hokkaido, northern Japan. Mass-specific testicular energy (kJ·g–1) was lower in migratory males than in mature parr in the Shikaribetsu population, but not in the Shumarinai population. The consistent pattern was observed in somatic energy, suggesting that mass-specific energy reflects population environment rather than inherent allocation pattern. Despite this confounding effect of specific energy, total testicular energy (kJ), relative to total somatic energy, was higher in mature parr in both populations. We suggest that strong sperm competition involved with sneak spawning is responsible for an increased testicular investment in mature parr.

Survival of Stream-Dwelling Atlantic Salmon: Effects of Life History Variation, Season, and Age

Abstract To determine seasonal and age-class variation in the abundance and survival of Atlantic salmon Salmo salar, we conducted multiple samplings of individually tagged juveniles in a small stream (West Brook, Massachusetts). We also estimated the differences in survival and probability of smolting for mature and immature parr. Survival was approximately twofold lower during winter as compared with summer and was higher for fish in their first winter than for fish in their second winter. Parr maturation rates were high (50% of all fish) and peaked in September. The estimated numbers of mature and immature fish were equal for the March samples preceding the smolt run, indicating no overall differences in survival between mature and immature fish during stream residence. Age-2 mature fish were one-third as likely to smolt as immature fish, however, resulting in survival probabilities (from March to smoltification) of 0.22 for mature fish and 0.61 for immature fish. Approximately one-third of the fish cap...

A method for tracking the behaviour of mature and immature salmon parr around nests during spawning

A remote monitoring system was developed to provide information on the behaviour of mature and immature Atlantic salmon Salmo salar parr at nests during the spawning season. An octagonal passive integrated transponder (PIT) detector (0·865 m maximum diameter) designed to surround nests of Atlantic salmon was used to identify individual salmon parr present at 38 spawning events in three circular spawning channels. The range of the detector for PIT tags presented in the optimum orientation was 2·4 cm (range between tags 1·7–3·0 cm). Using a sub‐sample of 20 spawnings, the mean efficiency of the detector (number of fish passes registered relative to number of passes observed on video) was 70·5% (range 32‐100%). There were no significant effects of time from spawning, total number of registrations, body size or maturity status (mature or immature) on efficiency. However, fish were more likely to be detected entering nests than leaving, as departures were more rapid and higher in the water column. The PIT detector did not affect the numbers of parr at spawnings or between spawning intervals of females, and allowed for the individual identification of 65 of the 72 parr observed in nests during spawning. In all cases where certain identifications were not possible and the video was of satisfactory quality, this was due to obstruction of the camera view by anadromous fish. The remote monitoring system was thus effective in identifying behavioural differences, and only one of 20 immature parr was ever detected during the period encompassing 10 min before and after spawning compared with 30 or 40 mature parr.

A method for tracking the behaviour of mature and immature salmon parr around nests during spawning

A method for tracking the behaviour of mature and immature salmon parr around nests during spawning