Field activity of lake trout during the reproductive period monitored by electromyogram radiotelemetry

Many lake trout Salvelinus namaycush spawn in shallow areas along windswept shores. However, precise determination of time and location of spawning is limited by its nocturnal occurrence, and possibly by some postulated, but unproven, spawning in deep water by certain populations. In White Pine Lake, Ontario, a well-studied experimental lake, lake trout spawn in two shallow locations where some direct observation is possible. Radiotelemetry apparatus was used in 1991 to obtain records of the electromyograms (EMGs) produced by muscle activity in one adult male and one adult female lake trout, captured from the lake before their reproductive period and returned to the lake at the beginning of the spawning period. Both fish survived, though only the male was detected as active over the main spawning site, where it showed evening EMG activity patterns indicating considerable activity. At other times of day, when not located over the spawning site, but present elsewhere in the lake, the male's EMG (i.e. muscle) values were considerably reduced. At the cessation of the spawning period, the transmitter-equipped male's EMG record showed no further pattern indicative of high activity during what had formerly been the daily spawning period. The female was tracked as she moved around the lake, but based on both her location and level of EMG activity, is thought not to have spawned. In 1992, a second male was captured, equipped with a transmitter and released again. This fish failed to show spawning activity but, as with the 1991 female, moved fairly considerable distances in the lake. In one instance, in a swim of short duration (6 min), well away from the spawning grounds, this fish displayed EMG activity levels resembling those of the high activity of spawning. The results obtained appear to demonstrate that EMG telemetry could be used to assess the level of muscular activity occurring in lake trout, especially in relation to reproductive behaviour, and when they cannot be directly observed.     

Seasonal changes in the epidermis of the brown trout Salmo trutta (L.)

A sexual dimorphism was found in the epidermis of hatchery-reared brown trout. The epidermis of both male and female fish undergoes rhythmical changes in thickness during successive spawning cycles. For most of the year the male has a significantly thicker epidermis than the female. During the spawning period (December and January) there is a highly significant drop in the concentration of mucous cells in the epidermis of the male brown trout. These findings are discussed in the light of our knowledge of the skin structure in other salmonid fish and in relation to possible hormonal factors influencing the epidermis of teleosts.     

A dynamic-bioenergetics model to assess depth selection and reproductive growth by lake trout (Salvelinus namaycush)

We coupled dynamic optimization and bioenergetics models to assess the assumption that lake trout (Salvelinus namaycush) depth distribution is structured by temperature, food availability, and predation risk to maximize reproductive mass by autumn spawning. Because the model uses empirical daily thermal-depth profiles recorded in a small boreal shield lake (lake 373 at the Experimental Lakes Area, northwestern Ontario) during 2 years of contrasting thermal stratification patterns, we also assessed how climate-mediated changes in lakes may affect the vertical distribution, growth, and fitness of lake trout, a cold-water top predator. The depths of acoustic-tagged lake trout were recorded concurrently with thermal-depth profiles and were compared to model output, enabling an assessment of model performance in relation to the observed fish behavior and contrasting thermal conditions. The depths and temperatures occupied by simulated fish most closely resembled those of the tagged fish when risk of predation was included in the model, indicating the model may incorporate the most important underlying mechanisms that determine lake trout depth. Annual differences suggest less use of shallow (warm), productive habitats, resulting in markedly less reproductive mass, during the year with the warm stratification pattern. Mass for reproduction may be lower in warmer conditions because of reduced reproductive investment, yet survival may be inadvertently higher because risky surface waters may be avoided more often in warmer, shallower, and metabolically costly conditions. At a minimum our study suggests that lake trout reproductive mass and fitness may be expected to change under the anticipated longer and warmer stratification patterns.     

Lymphocytopenia and interrenal activity during sexual maturation in the brown trout, Salmo trutta L.

In three different strains of brown trout a marked reduction in the number of circulating lymphocytes occurred in the blood of sexually mature male and female fish during the spawning season. This lymphocytopenia was closely correlated with elevated plasma cortisol levels in all three strains. It is well established that sexual maturation in salmonid fish is associated with an increase in susceptibility to disease: the present study provides strong evidence that this is mediated, at least in part, by a cortisol-induced suppression of lymphoid activity. These findings are discussed in relation to possible physiological roles of cortisol during the spawning period and to the evolution of semelparity in salmonid fish.     

Lake trout (<Emphasis Type="Italic">Salvelinus namaycush</Emphasis>) spawning behaviour: the evolution of a new female strategy

A video camera inside an underwater housing was used to record the spawning activities of lake trout, Salvelinus namaycush, in Kushog Lake, Ontario (Canada). Contrary to the commonly accepted belief describing lake trout as the only salmonine to spawn exclusively at night, the recordings were taken during the day. Lake trout spawning behaviour is described in detail and compared with other salmonine species. The loss of female “nest-building” and assumption of a novel itinerant strategy during which females travel across the breeding grounds accompanied by a group of males, is considered to be an important change in the evolution of the lake trout’s unique mode of spawning.     

Comparison of brook trout reproductive success and recruitment in an acidic adirondack lake following whole lake liming and watershed liming

Limestone applications to the catchment of one tributary to Woods Lake were highly effective in reducing stream acidity and stabilizing seasonal fluctuations in pH. The resulting improvement in stream water quality also led to a dramatic shift in reproductive strategy of the Woods Lake brook trout population. Prior to catchment liming, brook trout in Woods Lake were restricted to spawning on poor quality near shore substrate with limited ground water seepage. Reproductive success was limited by high mortality of eggs and larvae and recruitment from in lake spawning was not successful. Spawning brook trout did not utilize the tributary for spawning prior to watershed liming. Mitigation of acidity in the tributary, by catchment liming, effectively extended the spawning habitat available to the Woods Lake brook trout population and one year following treatment brook trout spawned successfully in the tributary for the first time in 6 years of observation. Significant recruitment of young trout into the lake population occurred from 1991 through 1993, although the absolute number of fish captured was relatively small. In the fall of 1993, four year classes of naturally spawned brook trout were present in the lake. Although reproductive success was enhanced by improving tributary spawning habitat in the Woods Lake basin, self maintenance of the population may be limited by low recruitment rates of young trout, due to high levels of summer mortality resulting from predation. Mitigation of this constraint would require substantially higher levels of fry production than were observed in Woods Lake and/or enhanced refugia for young trout. The results of this experiment suggest that re-establishment of tributary spawning populations of brook trout may be possible, with future reductions in acidic deposition, in acidic Adirondack lakes with limited in-lake spawning habitat.     

Seasonal changes in reproductive function of the rainbow trout (Salmo gairdneri)

The sequential changes in serum oestradiol 17β (measured by specific radioimmunoassay), vitellogenin (measured by phosphoprotein phosphorus content) and total calcium (measured by fluorimetry) in male and female rainbow trout under a simulated natural photoperiod cycle were investigated. Resting levels of 130 pg/ml serum oestradiol in both male and female fish were found in April and May. In the female, levels reached a peak of 4800 pg/ml in October, and almost returned to resting levels just prior to spawning in mid-January. No significant change from resting levels was seen in the male fish.
In both male and female fish levels of 25 μg/ml serum phosphoprotein phosphorus and 10–14 mg % total serum calcium were found from April to July. Coincident with the rise in oestradiol 17β, in the females serum levels of phospho-protein phosphorus and total calcium increased to 400 uβg/ml and 58 mg% respectively just prior to spawning. In the males no significant change in either of these values was observed throughout the cycle. These results strongly support the hypothesis that photoperiod is the major factor in the environmental control of reproductive activity in the rainbow trout.     

Breeding success of male brook trout (Salvelinus fontinalis) in the wild

Competition for females generally results in some males adopting alternative reproductive tactics to acquire matings. For fish, the ecological and evolutionary consequences of these tactics are not well understood because of an inability to link directly the interactions of individuals on the breeding grounds with genetic data. This study combines behavioural observations with genetic estimates of male reproductive success within an intensively studied wild population of lacustrine brook trout (Salvelinus fontinalis). Male brook trout exhibit a conditional reproductive strategy with small males adopting a peripheral position to that of larger dominant males in their proximity to spawning females. Parentage analysis of eggs collected from wild redds confirmed the reproductive success of individual males. Males relegated to peripheral positions during spawning participated frequently in spawning events, but in most cases the first male to spawn was the sole contributor, and no more than two males contributed successfully to a single brood. While behavioural observations of salmonines suggests that reproduction is partitioned among males in a manner dependent upon body size and proximity to spawning females, the genetic evidence from this study suggests a more limited distribution of reproductive success in the field. The genetic contributions of male brook trout are highly skewed towards larger males for this population. A review of the salmonine literature suggests little difference in individual reproductive success for males exhibiting size-related tactics within a conditional mating strategy vs. precocial maturation. Collectively, these genetic studies provide new insights on the evolution of alternative life histories among salmonines.     

人工模拟产卵环境中青海湖裸鲤的繁殖行为

研究通过人工产卵环境模拟, 成功诱导青海湖裸鲤(Gymnocypris przewalskii)自然产卵受精, 通过标志跟踪和视频监控等方法对青海湖裸鲤的繁殖行为进行了研究。结果表明, 青海湖裸鲤的繁殖过程包含了追逐、伴游、潜尾、溅戏和交尾等典型行为。其中溅戏行为(单尾雌鱼或雄鱼背鳍露出水面并用尾部拍击水面)首次被观察确认, 常被误认为是交配行为。追逐、伴游、潜尾和溅戏等繁殖行为平均频次分别为: 5.7、14.7、9.3和3.5 次/d。通过采用不同性比重复配对实验发现, 在观测到的34次交配行为中, 32次(94.1%)均为1雌和1雄配对交配。研究还发现性成熟的雌性青海湖裸鲤为一次产卵类型, 短时间内多次交尾排卵, 雌雄交配(排卵授精)行为约每天3—9次, 每次排卵耗时约4—9s, 每次平均排卵量131粒(范围15—376), 每尾雌鱼可连续交配产卵3—7d。观测到34次的交配行为中, 31次(91.1%)均发生在夜间(23: 00—次日2: 00), 3次(8.9%)发生在白天(早晨6:00—7:00)。研究首次基于人工模拟产卵环境观察描述了青海湖裸鲤的繁殖行为特征, 可为青海湖裸鲤人工产卵场构建、自然繁殖监测和产卵场保护提供科学依据。     

Oxygen consumption of active rainbow trout, Salmo gairdneri Richardson, derived from electromyograms obtained by radiotelemetry

A radiotelemetry apparatus is described for sensing and transmitting electromyograms (EMGs) from free-swimming fish. EMGs are recorded from the epaxial muscles of adult rainbow trout during periods in spontaneous (= routine) activity, and forced-swim, respirometers. When such EMG records are integrated, subjected to spectral analysis, and computer-averaged, the EMG values (in μV) are highly correlated with the fish oxygen consumption during the activity periods. However, there is a marked difference between the regression slopes for oxygen v . EMG value for the data from the spontaneous, and forced-swim, respirometers; the former slope is the steeper. The probable explanation of this phenomenon is that whereas in forced swims the epaxial myomeres are responsible for most of the activity of the fish, in spontaneous activity other muscle systems (e.g. of the lateral, dorsal and ventral fins) come to account for a greater relative proportion of body movement. The difference in slope, although great, is evidently a regular phenomenon. The shift from one regression to the other occurs at a fairly precise epaxial EMG value ( c . 5 μV). This suggests that the laboratory calibration of EMG value in terms of oxygen consumption can be utilized in the wild so that EMG records from free-swimming fish, fitted with telemetry packages can be used to deduce oxygen consumption attributable to activity. It also appears that such records can be used as a guide to the type of activity of the fish, i.e. desultory movements or free cruising.     

Sexual differences in the incidence and severity of ectoparasitic infestation of the brown trout, Salmo trutta L.

Hatchery-reared and wild brown trout, Salmo trutta L., were examined for skin ectoparasites during their spawning period in 1977 and 1978. A total of eight genera of parasites, comprising five ciliates, one flagellate, one monogenean and one parasitic fungus, were identified with as many as five different genera occurring on a single fish. Sexually mature male fish were more frequently or more severely infested by species of Ichthyophthirius, Scyphidia, Gyrodactylus and Saprolegnia than were immature fish of either sex or mature female fish. The differences in ectoparasitic loading could not be correlated with known, seasonal changes in the mucus-producing potential of the epidermis. These findings are discussed in relation to the defence mechanisms of teleost fish and to some of the endocrinological changes that occur in salmonid fish during the spawning season.     

Stress reduces the quality of gametes produced by rainbow trout.

In this study we have used the rainbow trout as a model animal to study the biological consequences of stress in terms of gamete quality and quantity. Groups of 30 mature male and female rainbow trout were subjected to repeated acute stress during the 9 mo prior to spawning. Time of ovulation, fecundity, and egg size were recorded in mature females, and sperm counts were carried out on the milt from the male fish, from both the stressed and control groups. Eggs from ovulated females were fertilized with milt from males subjected to the same treatment regime. Approximately 300 eggs from each female were fertilized with a sperm dilution of 10(-3) in diluent. Subsequent development of the fertilized eggs was then monitored. There were no differences in somatic weight or length between the two groups at the end of the experiment, but exposure of rainbow trout to repeated acute stress during reproductive development resulted in a significant delay in ovulation and reduced egg size in females, significantly lower sperm counts in males, and, perhaps most importantly, significantly lower survival rates for progeny from stressed fish compared to progeny from unstressed control fish. Hence, stress reduces the quality of gametes produced by rainbow trout.     

Gonad development and size‐at‐maturity of silver therapon Leiopotherapon plumbeus (Kner 1864; Teleostei:Terapontidae) in tropical volcanic lakes in south Luzon,Philippines

Gonad development of the silver therapon Leiopotherapon plumbeus in two volcanic crater  lake  habitats (Sampaloc Lake, Taal Lake) in south Luzon, Philippines was examined during the annual reproductive cycle. The minimum body size‐at‐maturity of fish in these two lake habitats was also compared. Four gonad development stages were characterized as basis for the classification of ovarian (immature, maturing, mature, spawned) and testicular maturation (immature, maturing, mature) phases. The occurrence of all development stages in individual gonads suggest an asynchronous development whereby advanced stages are recruited continuously from a pool of younger stage germ cells to result in elevated female and male GSI throughout the annual cycle due to active gonadogenesis. Together with the increasing occurrence of advanced stage oocytes and spermatozoa from March until October, the elevated GSI of fish may indicate peak gonadal growth during the onset of the dry season (December–January) for eventual spawning from the beginning (May–June) until the end of the wet season (October–November). In both lake habitats, male fish were smaller than females but, regardless of sex, the minimum size‐at‐maturity of fish in Sampaloc Lake was significantly smaller than fish in Taal Lake. Overall, asynchronous development during oogenesis and spermatogenesis allows for year‐round reproduction of silver therapon, with elevated gonad growth in the dry season in preparation for spawning during the wet season. Compared with fish in Taal Lake, a smaller size‐at‐maturity of fish in Sampaloc Lake may be a response of the wild fishery stock to long‐term high fishing mortality and degradation of the lake habitat.     

Seasonal variations of activity pattern of brown trout (Salmo trutta) in a small stream, as determined by radio-telemetry

Nine brown trout (27.9–42.8 cm FL, 234–995 g) from the Aisne stream (Belgian Ardenne) were tagged with surgically implanted radio transmitters, and their activity patterns were studied at 10-min intervals during twenty-six 24-h cycles from October 1995 to May 1997. The duration and intensity of activity were mainly proportional to water temperature and day length but some differences appeared between individuals. The daily home range in summer was also 3.2 times longer than in winter, and was exploited 2.5 times more intensively. At all seasons, trout were most active at dusk, and seasonal variations in diel patterns consisted mainly in a progressive shift from more crepuscular activity in autumn and winter to more homogenous and intensive activity during spring and summer, but still with a predominance of activity at dusk. This relative consistency of activity rhythm throughout the year was interpreted within the context of foraging risk and efficiency, in view of the scarcity of predators in the Aisne stream, and of drifting macroinvertebrates being consistently more abundant at dusk at all times of the year. However, activity patterns varied substantially between individuals living in different microhabitats, including when fish were investigated on the same day. This suggests that activity patterns are also subordinated to local factors such as habitat structure or abundance of drifting prey.     

Diffusion in the littoral zone: scoping emergence times and movement to essential habitat for young‐of‐year brook trout in lakes

Factors governing the process of dispersal of lake‐spawned brook trout ( Salvelinus fontinalis ) young‐of‐year (YOY) appear drastically different from those governing dispersal in more commonly studied stream salmonids. Rather than dispersal being highly density‐dependent and the result of territoriality and aggression, in brook trout it may be density‐independent and driven by a common need for coldwater habitat for summer survival. Emerging fish travel great distances from single spawning sites on lakes to cold groundwater habitat. Movement is a gradual, one‐dimensional diffusion around lake margins and represents a very unique and simplified natal dispersal pathway allowing for dispersal rates, distances, and factors controlling these parameters to be measured. We predicted timing of the emergence period for brook trout alevins from lake spawning sites using the known relation between water temperature and emergence times for salmonids. Emergence and dispersal was then observed in the field by visually estimating YOY density in segments of the littoral zone throughout the dispersal period. Fluxes in density in these sections were used to estimate rate of YOY spread. YOY behaviour and body condition was also assessed across the wave of spatial spread. We are working towards a spatially explicit model to identify critical groundwater rearing habitat needing protection from forestry activities.     

Scatter-spawning of the catfish,Silurus asotus

Reproductive behaviour of the catfish,Silurus asotus was studied in temporary waters around paddy fields. Spawning occurred nocturnally during the first week from the initiation of irrigation. In reproductive activities, a male first energetically pursued a female with its head near to the female’s belly (chasing) and then began to cling to the female’s body from the side, bending its tail or head (clinging). Finally the male enfolded the female’s body, with its anus near to the female’s (enfolding). In some cases, 2–4 males pursued a single female and two males enfolded a female at the same time. Although no aggressive behaviour was evident between males, it was always the largest male that could most frequently approach and enfold the female. The mating pair moved a long distance in a ditch, paddy field and/or creek, performing reproductive activities. It is thought that the spawning site and period of spawning of the fish enable the larvae to avoid the danger of predation and to efficiently feed, firstly on plankton and later on larvae of other fishes which become abundant during the irrigation period. Although some eggs and larvae may die due to the drying out or high water temperatures of such unstable temporary waters, scattering eggs may reduce the incidence of the annihilation of the young.     

Temporal constraints on the potential role of fry odors as cues of past reproductive success for spawning lake trout

Deciding where to reproduce is a major challenge for most animals. Many select habitats based upon cues of successful reproduction by conspecifics, such as the presence of offspring from past reproductive events. For example, some fishes select spawning habitat following odors released by juveniles whose rearing habitat overlaps with spawning habitat. However, juveniles may emigrate before adults begin to search for spawning habitat; hence, the efficacy of juvenile cues could be constrained by degradation or dissipation rates. In lake trout (Salvelinus namaycush), odors deposited by the previous year's offspring have been hypothesized to guide adults to spawning reefs. However, in most extant populations, lake trout fry emigrate from spawning reefs during the spring and adults spawn during the fall. Therefore, we postulated that the role of fry odors in guiding habitat selection might be constrained by the time between fry emigration and adult spawning. Time course chemical, physiological, and behavioral assays indicated that the odors deposited by fry likely degrade or dissipate before adults select spawning habitats. Furthermore, fry feces did not attract wild lake trout to constructed spawning reefs in Lake Huron. Taken together, our results indicate fry odors are unlikely to act as cues for lake trout searching for spawning reefs in populations whose juveniles emigrate before the spawning season, and underscore the importance of environmental constraints on social cues.     

Plasma Nesfatin-1 Is Not Affected by Long-Term Food Restriction and Does Not Predict Rematuration among Iteroparous Female Rainbow Trout (Oncorhynchus mykiss)

The metabolic peptide hormone nesfatin-1 has been linked to the reproductive axis in fishes. The purpose of this study was to determine how energy availability after spawning affects plasma levels of nesfatin-1, the metabolic peptide hormone ghrelin, and sex steroid hormones in rematuring female rainbow trout (Oncorhynchus mykiss). To limit reproductive maturation, a group of female trout was food-restricted after spawning and compared with a control group that was fed a standard broodstock ration. The experiment was conducted twice, once using two-year-old trout (second-time spawners) and once using three-year-old trout (third-time spawners). During monthly sampling, blood was collected from all fish, and a subset of fish from each treatment was sacrificed for pituitaries. Pituitary follicle-stimulating hormone-beta (fsh-β) mRNA expression was analyzed with q-RT-PCR; plasma hormone levels were quantified by radioimmunoassay (17β-estradiol and ghrelin) and enzyme-linked immunosorbent assay (11-keto-testosterone and nesfatin-1). Although plasma nesfatin-1 levels increased significantly in the months immediately after spawning within both feeding treatments, plasma nesfatin-1 did not differ significantly between the two treatments at any point. Similarly, plasma ghrelin levels did not differ significantly between the two treatments at any point. Food restriction arrested ovarian development by 15–20 weeks after spawning, shown by significantly lower plasma E2 levels among restricted-ration fish. Pituitary fsh-β mRNA levels were higher among control-ration fish than restricted-ration fish starting at 20 weeks, but did not differ significantly between treatment groups until 30 weeks after spawning. Within both treatment groups, plasma 11-KT was elevated immediately after spawning and rapidly decreased to and persisted at low levels; starting between 20 and 25 weeks after spawning, plasma 11-KT was higher among control-ration fish than restricted-ration fish. The results from these experiments do not provide support for plasma nesfatin-1 as a signal for the initiation of reproductive development in rematuring female rainbow trout.     

Environmental and lunar cues are predictive of the timing of river entry and spawning-site arrival in lake sturgeon Acipenser fulvescens

The associations were quantified between daily and interannual variation in the timing of a closed population of lake sturgeon Acipenser fulvescens migration and arrival at spawning sites with stream environmental and lunar covariates. Spawning data were gathered from 1262 fish in Black Lake, Michigan 2001 to 2008 and by video monitoring 2000 to 2002. Sex-specific variation in responses to external cues was also tested. Results showed that a greater number of individuals initiated migration from lake to riverine habitats at dawn and dusk relative to other times of the day. Current and lagged effects of water temperature and river discharge, and periods in the lunar cycle were important variables in models quantifying movements into the river and timing of adult arrival at spawning sites. Different suites of covariates were predictive of A. fulverscens responses during different periods of the spawning season. The timing of initiation of migration and spawning, and the importance of covariates to the timing of these events, did not differ between sexes. Stream flow and temperature covaried with other variables including day length and the lunar cycle. Anthropogenic disruption of relationships among variables may mean that environmental cues may no longer reliably convey information for Acipenseriformes and other migratory fishes.