Trout Stocks Research Articles

Evaluation of incubation temperatures on DNA damages of the Caspian trout (Salmo trutta caspius Kessler, 1877) single cells through developmental stages by Comet assay

Caspian trout (Salmo trutta caspius Kessler, 1877) is an endemic migratory subspecies in the Caspian Sea, possessing ecologic-economic and biodiversity greatly value. Among habitat factors, temperature and its possible effects on the Caspian trout genome were considered in this research. During Embryonic developmental stages (fertilization–hatching), genomic alterations of single cells were assessed by Comet assay technique in three thermal treatments (4, 8, 12oC). After artificial propagation of wild broodstocks, the batches of eggs (No. 500), were transferred to well equipped incubators with constant temperatures, water recycling systems by REDD(spawning area of trout)water, 3 stages water filtration (Si+Active Coal+Zeolite), UV-C application on effluent of each incubator and DO – pH – temperature digital controllers in 3 replicates. Samples were collected from normal (8°C), cold (4°C) and warm (12°C) treatments on eyed egg, alevin and larval stages. Single Cell Gel Electrophoresis technique were applied on samples for evaluation of Comet Tail length (TL), DNA in tail (DT) and Tail Moment (TM) indexes (CometScore software ©2013 TriTek Corp) as DNA damage markers. Significant difference between thermal treatments (P<0.05) and comparison between mean values of comet TL index indicated 85.19 ±9.2 , 9.88 ±2.3 and 256.54±14.6 for 4, 8 and 12°C treatments, respectively. DT mean values measured as 18.07±6.3, 9.72±1.9 and 31.47±2.8 and then TM mean values measured as 15.27± 4.1, 1.21±0.2 and 95.25±8.6 for 4, 8, and 12°C treatments respectively. Warm (12°C) treatments demonstrated greater DNA damages in comparison to the others. TM explained better information in comparison with TL & DT in all analyzed samples. In conclusion, temperatures out of optimal thermal conditions could significantly affect Caspian trout genome which could be subject of management considerations pertaining to Caspian trout stocks rehabilitation and captive rearing strategies.

Predator–prey dynamics mediate long-term production trends of cisco (Coregonus artedi) in a northern Wisconsin lake

We quantified production, biomass, and production to biomass (P/B) ratios for cisco (Coregonus artedi) in Trout Lake, Wisconsin, USA (2001–2015). Across all years, annual production, biomass, and P/B were variable ranging 0.6–30.2 kg·ha−1·year−1, 1.2–39.7 kg·ha−1, and 0.4–0.9·year−1, respectively. Cisco production exhibited obvious decline. However, neither biomass nor P/B changed significantly over time. Long-term patterns of environmental conditions remained unchanged during the study and were unrelated to cisco production. However, lake trout (Salvelinus namaycush) relative abundance showed a strong inverse relationship with cisco production and biomass. Intense lake trout stocking has occurred in this lake over time to conserve a genetically unique strain of the species. These management efforts may have had the unintended consequence of amplifying top-down predation on cisco. Since cisco P/B has gone largely unchanged, cisco production would be predicted to rebound quickly to adaptive reductions in lake trout stocking. Further increases in lake trout numbers could place both populations at risk of collapse. This study provides an example of a fisheries production approach for understanding and conserving cold-water fisheries, especially in lakes dominated by ciscoes.

Evaluating the Trade‐Offs between Invasion and Isolation for Native Brook Trout and Nonnative Brown Trout in Pennsylvania Streams

AbstractA popular conservation strategy for native trout species in western North America is to prevent invasions by nonnative trout by installing barriers that isolate native trout populations into headwater streams. In eastern North America, native Brook Trout Salvelinus fontinalis are frequently replaced in coolwater habitats by nonnative Brown Trout Salmo trutta and relegated to small headwater streams. In this study, we compared the effects of isolation and invasion by nonnative Brown Trout on the distribution and demographic structure of Brook Trout populations from 78 trout streams in northwestern Pennsylvania. The Brook Trout and Brown Trout distributions varied in predictable ways along the stream size gradient, with Brown Trout becoming dominant in larger streams. However, there was a prominent barrier effect, with streams 12 times more likely to have Brook Trout than Brown Trout when a downstream barrier was present between the sample site and the nearest Brown Trout stocking location. In comparison, 91% of the streams with Brown Trout had no downstream barrier, suggesting that barriers are important in creating refugia for Brook Trout. Brown Trout also appeared to have a negative impact on Brook Trout population demographics, as Brook Trout populations in sympatry with Brown Trout had fewer age‐classes and lower population densities than allopatric Brook Trout populations. Isolating Brook Trout to small headwater streams with downstream barriers that prevent Brown Trout invasion could be a viable conservation strategy in regions where barriers would serve to reduce the negative impacts from Brown Trout. Since barriers could further fragment local Brook Trout populations, however, they would need to be strategically placed to allow for seasonal movements to maintain metapopulation structure and ensure population persistence.

Pike (Esox lucius) stock management in designated brown trout (Salmo trutta) fisheries: Anglers’ preferences

The sustainable management of fisheries is increasingly as much about people as it is about stock management and an important prerequisite for managing stakeholder disagreement is an understanding of each party's position and perspective. In Ireland pike stocks are actively managed within specific fisheries for the purpose of protecting brown trout stocks. Associated public discussion is increasingly polarized with a clear message that trout anglers favour and pike anglers oppose such management intervention. A first step towards successfully managing the tension between all stakeholders is a better understanding of the broad spectrum of anglers’ views. Latent-class site-choice models are estimated with choice experiment data to reveal information on anglers’ preferences with the data collected via an online survey from 341 members of a recreational angling research panel. Several policy relevant lessons arise from the analysis. First, anglers’ preferences are not homogeneous, either among pike or trout anglers. Angler stakeholder groups cannot reasonably attest to represent all pike or trout anglers. There are multiple distinct classes of anglers with quite different preferences on pike stock control as well as other fishery attributes, such as bag limits and catch rates. Second, while anglers have strong preferences across a number of fishery attributes (e.g. catch rates, pollution, invasive weeds, etc.), pike stock control is the predominant attribute affecting anglers’ behaviour. Third, among trout anglers there is a sizeable majority opposed to the maintenance of existing pike stock control measures, which is at odds with a vociferous public campaign led by trout angling representative organizations. The preferences of this ‘silent’ majority reflect the fact that approximately 2-in-5 trout anglers also fish for pike. In general, the research helps inform fishery management decisions, dispelling the idea of a clear dichotomy between pike and trout anglers and instead illuminates the complexity of anglers’ preferences.

Inland fish stock assessment: Applying data‐poor methods from marine systems

AbstractInland fisheries can be diverse, local and highly seasonal. This complexity creates challenges for monitoring, and consequently, many inland fish stocks have few data and cannot be assessed using methods typically applied to industrial marine fisheries. In such situations, there may be a role for methods recently developed for assessment of data‐poor fish stocks. Herein, three established data‐poor assessment tools from marine systems are demonstrated to highlight their value to inland fisheries management. A case study application uses archived length, catch and catch‐per‐unit‐effort data to characterise the ecological status of an important recreational brown trout stock in an Irish lake. This case study is of specific use to management of freshwater sport fisheries, but the broader purpose of the paper was to provide a crossover between marine and inland fisheries science, and to highlight accessible data‐poor assessment approaches that may be applicable in diverse inland systems.

Long-Term Trends in Abundance and Size of Sport Fishes in the Flathead River, Montana, Following Changes in Hydroelectric Dam Operations

We studied long-term trends in catches per unit effort (CPUE; fish h-1) of four sport fish taxa in the Flathead River, Montana, following changes in hydroelectric operations at the Slis Ksanka Qisp Project (SKQP; formerly Kerr Dam). Prior to 1997 SKQP operations caused frequent, unnatural flow fluctuations. In 1997 the dam was changed from a power-peaking and load-following facility to a base-load facility. The new operations included seasonal minimum flows and ramping rates that greatly reduced flow fluctuations. Autumn trends in CPUEs of two size classes (substock and stock) of northern pike (Esox lucius), Oncorhynchus spp., brown trout (Salmo trutta), and smallmouth bass (Micropterus dolomieu) were monitored using nighttime electrofishing during 1984–86 before operational changes and again at the onset of operational changes in 1998 and continuing through 2008. We observed little difference in CPUEs between 1984–86 and 1998, the first year after changes, but we documented strong increasing trends in CPUEs of both sizes of all taxa, except stock northern pike, over the long term following operational changes. We also examined long-term patterns in the size structure (total length; TL mm) of fishes following operational changes. All taxa had either initial downward shifts in median TL, decreases in minimum sizes of fish captured, or both, a pattern consistent with enhanced recruitment and survival of smaller fishes. We conclude that modifications in dam operations were associated with increases of four sport fish taxa in the Flathead River and that similar normative flow applications might benefit riverine fish populations elsewhere.

Survival and Reproductive Success of Hatchery YY Male Brook Trout Stocked in Idaho Streams

AbstractNonnative Brook Trout Salvelinus fontinalis were introduced throughout western North America in the early and mid 1900s, resulting in populations that are difficult to eradicate and that often threaten native salmonids. Male YY Brook Trout (MYY), created in the hatchery by feminizing XY males and then crossing them with normal XY males, comprise a novel approach to eradicating undesirable Brook Trout populations. If stocked MYY Brook Trout survive and reproduce with wild females, it could eventually drive the wild population sex ratio to 100% males, at which point the population would be unable to reproduce and would be eradicated after stocking ceased. In this study, we stocked the limited number of catchable‐size (mean TL = 229 mm) MYY hatchery Brook Trout available from an established MYY broodstock into four streams. In two streams, the wild Brook Trout population was suppressed via electrofishing prior to stocking to determine whether diminished competition with wild fish would increase the survival of hatchery MYY fish. We used genetic assignment testing to identify the successful reproduction of stocked MYY fish. Apparent survival of MYY Brook Trout averaged 18% in streams with wild population suppression (mean suppression, 17%) and 9% in streams without suppression, suggesting that suppression of the wild population before stocking increased MYY survival poststocking. Hatchery MYY Brook Trout comprised an estimated 3.1% of all adult Brook Trout during spawning. Genetic assignment tests identified successful reproduction of MYY fish in all streams in which they were stocked, with an average of 3.7% of fry being the progeny of MYY fish. Our results confirm that hatchery MYY fish stocked in streams can survive and spawn successfully with wild fish and produce all‐male progeny. Despite the slightly reduced fitness of MYY Brook Trout, this technology may be a viable method for eradicating undesirable nonnative Brook Trout populations.

Angler effort response to sterile rainbow trout stocking in small BC lakes

Angler effort responses to the stocking of sterile rainbow trout were evaluated using a historical data set consisting of 63,000 angler boat counts, which were used to develop indices of annual angler effort for 513 lakes representing 3396 lake-years of data over a period of 25 years. Included in this data set were 173 lakes that were supported by put-and-grow stocking of rainbow trout, and that received diploid (2n) stocking in earlier years and triploid (3n) stocking in later years. A stocking-size-dependent, ploidy-independent, growth and survival model was used to estimate the number of fish available to anglers one and two years post-stocking. Following a change to triploid stocking, boat counts increased by 31%, with larger increases in more remote Regions. Boat counts declined through time by 0.988x/yr, but with substantial variation among years (SD = 0.124). A principal component synthesized from four correlated variables (license cost, license sales, gas price, Can$:US$) explained 35% of the residual variation in boat counts among years. The boat count response to fish abundance was positive for rainbow trout, at 0.20x of the proportional change in abundance. An index of size-and-quota regulation intensity ranging from 0 (general restrictions only) to 1 (catch and release only), indicated that boat count response was positive, at 1.17x of the proportional increase in regulation intensity.

Habitat degradation and trout stocking can reinforce the impact of flash floods on headwater specialist Alpine bullhead Cottus poecilopus - A case study from the Carpathian Mountains

In freshwater streams, flooding is a typical source of natural disturbance that plays a key role in the dynamics of animal populations and communities. However, habitat degradation and fish stocking might increase the severity of its impact. We tested the effects of a flash flood on the abundance of three size classes of headwater dwelling Alpine bullhead, Cottus poecilopus, in the streams of the Carpathian Mountains in the Czech Republic, that are stocked with hatchery-reared brown trout, Salmo trutta. We showed that the overall abundance of Alpine bullhead was highest at the sites with the least degraded habitat (i.e., natural habitat) and we caught almost no Alpine bullhead at the sites with the most degraded habitat. The flash flood had a strong negative effect on the abundance of the largest individuals of Alpine bullhead. Abundance of small and medium size Alpine bullhead was negatively affected by the abundance of adult stocked brown trout before as well as after the flash flood. However, negative effect of adult brown trout abundance on abundance of large Alpine bullhead was not significant before the flash flood, and it became significant after the flash flood. This could indicate an accumulation of negative impacts of trout stocking and flash flood on this size class. Overall, our results suggest that stocking of hatchery trout and habitat degradation can reinforce the impact of flash floods on the population of Alpine bullhead in the streams of the Carpathian Mountains.

Distribution of non-native brook trout (Salvelinus fontinalis) across Norwegian waterbodies – is it an invasive species?

Non-native brook trout (Salvelinus fontinalis MITCHILL, 1815) was introduced into Norway in 1883. However, it was not until the late 1970s that this acid-tolerant salmonid species was stocked into many acidified lakes that many populations became established. In 2004, all brook trout stocking in Norway ceased. In this study, we surveyed the distribution of brook trout in Norwegian water bodies. A totally of 202 self-sustaining populations were identified, mostly in unregulated lakes (n=101), streams (n=71) and also to some extent in reservoirs (n=25). Only four populations were found in inland rivers, and one population in a river with Atlantic salmon (Salmo salar L.). Localities with brook trout covered a wide range of altitudes and sizes. Analyses of time-series catches in sympatric populations of brown trout (Salmo trutta L.) and brook trout from 12 lakes (1997-2012) revealed a strong decline in brook trout stocks. A similar development in abundance has also emerged from other studies in recent years. Generally, lake-dwelling brook trout is regarded as a low-risk species with respect to invasiveness. However, brook trout/brown trout interactions may be habitat-specific, as brook trout may dominate in small and relatively cold streams.

Variation in angler distribution and catch rates of stocked rainbow trout in a small reservoir.

We investigated the spatial and temporal relationship of catch rates and angler party location for two days following a publicly announced put-and-take stocking of rainbow trout (Oncorhynchus mykiss). Catch rates declined with time since stocking and distance from stocking. We hypothesized that opportunity for high catch rates would cause anglers to fish near the stocking location and disperse with time, however distance between angler parties and stocking was highly variable at any given time. Spatially explicit differences in catch rates can affect fishing quality. Further research could investigate the variation between angler distribution and fish distribution within a waterbody.

Problems Threatening the Tigris Trout (Salmo tigridis Turan, Kottelat &amp; Bektaş, 2011) Stock in Çatak Stream and Some Recommendations

This study was carried out to reveal the problems threatening Salmo tigridis stock inhabited in Çatak Stream and to offer some solutions to overcome these problems. Çatak is the largest stream of the region and located at 81 km southern of the Van city center. Salmo tigridis , which is only distributed in Çatak and Bahçesaray streams, faces the danger of extinction. In this study, it was observed that sand-graveling activities at Çatak Stream muddied the stream and destroyed appropriate reproduction habitats. Another problem is that Çatak Stream's over-destruction of vegetation in the catchment basin increases flood risk and flood-related sudden flow increases. In addition, it was determined that studies carried out for river improvement and flood control disturbed the natural flow regime of the stream, leading to deterioration in the base and coastal structure. Another threat is the rainbow trout ( Oncorhynchus mykiss ) that escape from fish farms. Catching with prohibited methods and fishing gears is also a problem that threatens the future of native trout stock in the stream. With this study, the problems that threaten the tigris trout stock in Çatak Stream were identified and some proposals were presented.

Large negative effect of non-native trout and minnows on Pyrenean lake amphibians

High mountain lakes are mostly naturally fishless ecosystems that have received numerous trout introductions over the world. Extensive studies mostly developed in west North America have shown a large negative effect of these introductions on amphibians, although no extensive studies are available from other continents such as Europe. Fish were also introduced extensively in the Pyrenees (southern Europe), mainly trout for angling and minnows for their use as live bait for fishing trout. We studied the effect of non-native trout and minnows on the occurrence of amphibian species inhabiting Pyrenean lentic habitats. Chi-square tests and Generalized Additive Models were applied on a dataset of 12 environmental descriptors from 1739 water bodies surveyed from 2006 to 2016. After accounting for environmental characteristics we found a large negative effect of non-native trout and minnows on Pyrenean amphibians. Trout was negatively associated with four of the six studied species. Since minnows were only introduced in trout present lakes, they were only significant for Rana temporaria, the most distributed amphibian in the area. None of the palatable amphibians have been able to recolonise the lakes where minnow remain as the only fish species indicating a strong negative effect. Minnow is the non-native fish with a higher introduction rate in the mountain range indicating that it might be a threat for other species in the future. Therefore, the control of trout stocking and minnow release in high mountain lakes is necessary to preserve European and worldwide amphibian populations in these ecosystems.

Justification for retention of the catch-and-release in the wild brown trout Salmo cf. trutta fishery

Total catch-and-release (C&R) is a regulatory measure implemented for maintaining the self-sustainability of stocks encountering strong fishing pressure. The River Đetinja is a tailwater with very strong fishing pressure, managed for more than a decade by C&R. That fishing regime was questioned by a new fishery manager, without the justification provided. The only available data for examining the brown trout growth were those from catches of two fly fishermen over five consecutive years. Only in one year did the average catch of one fisherman slightly surpass the legal limit for taking brown trout, and in none of years was the average size of pooled catches close to it. Survival data were similar, suggesting the stability of the brown trout stock through the period of investigation. Asymptotic length L∞ gradually increased and coincided with the growth speed ϕ and maximal yield length Lopt values. In spite of that, the high fishing pressure and low proportion of brown trout above both the legal taking limit of ≥25 cm SL and Lopt values in catches strongly support the retention of C&R as a regulatory measure on the River Đetinja.

Diversity of brown trout Salmo cf. trutta in the River Danube basin of Western Balkans as assessed from the structure of their mitochondrial Control Region haplotypes

The part of the River Danube basin in the Western Balkans region (11 sampled localities and 57 in total with using of published data) revealed the remarkable diversity of brown trout assessed using the Control Region (CR) of mitochondrial DNA (mtDNA) as a molecular marker. The greatest number of brown trout populations holds brown trout of the Da1 haplotype. Particular distinct haplotypes are limited to isolated brown trout stocks. There are haplotypes of Danubian (Da), and those of Atlantic (At), Adriatic (Ad) and marmoratus (MA) lineages introduced there. Phylogenetic relationships inferred between them implicate the plesiomorhic character of Da*Vr, Da*Dž and Da-s6 haplotypes that were resolved as ancestral clades, with the intermediate position between clades holding haplotypes of the non-Danubian lineage and more advanced haplotypes of the Danubian lineage. A uniform rate of evolution was found for all clades. The recent widespread distribution and exclusivity of Da1 haplotype imply its ancestral character among advanced Danubian haplotypes. Populations in the Sava, Drava, Una and Drina revealed an expansion, whereas those in the Kupa and Zapadna Morava catchments revealed both stability in size and great differentiation. Gene flow between stocks was found to be negligible.

Food Web Interactions Associated With a Lahontan Cutthroat Trout Reintroduction Effort in an Alpine Lake

Abstract Fisheries managers have stocked Lahontan Cutthroat Trout Oncorhynchus clarkii henshawi into Fallen Leaf Lake, California, since 2002 in an attempt to reestablish a naturally reproducing lacustrine population. However, the food web in Fallen Leaf Lake has been altered by the past introduction of nonnative species that may prey on or compete with reintroduced Lahontan Cutthroat Trout. Therefore, we used a combination of stomach content and stable isotope analyses to evaluate trophic characteristics within the aquatic species assemblage in Fallen Leaf Lake. Lahontan Cutthroat Trout preyed on mysid shrimp Mysis diluviana, aquatic insects, terrestrial arthropods, signal crayfish Pacificus leniusculus, and fishes. Diet overlap was greatest between Lahontan Cutthroat Trout and Mountain Whitefish Prosopium williamsoni; however, these species exhibited a generalized feeding strategy that may allow them to partition prey resources in order to avoid competitive interactions. Nonnative Lake Trout Salvelinus namaycush and Brown Trout Salmo trutta are top-level predators in Fallen Leaf Lake and both consumed Lahontan Cutthroat Trout during this study. Lake Trout δ13C and δ15N increased following Lahontan Cutthroat Trout stocking, a change consistent with incorporating isotopically enriched Lahontan Cutthroat Trout into their diet. Managers should consider the effects of predation by Lake Trout and Brown Trout on Lahontan Cutthroat Trout when developing future management and stocking programs for Fallen Leaf Lake. Additionally, intentional manipulation of the isotopic composition of hatchery-reared fish prior to stocking may be useful for evaluating predation in Fallen Leaf Lake and other systems.

The genetic approach for assessing sea trout stock enhancement efficiency – An example from the Vistula River

Abstract Many countries in the Baltic Sea basin have initiated enhancement programs for Baltic migratory sea trout, Salmo trutta L., to compensate for losses stemming from anthropogenic pressure that has resulted in the declining population abundance of this species. Regular stock enhancement has been conducted in Poland since the 1960s. Currently, over one million sea trout smolts are released into Polish rivers annually. In most Baltic countries, including Poland, stock enhancement depends on hatcheries producing material using spawners caught in native rivers. However, increasing difficulty obtaining spawners in recent years in Poland has meant that stock enhancement performed in the Vistula has been done largely with material obtained from broodstocks. Simultaneously, there is a lack of information regarding the proportion of wild and cultured sea trout in this river basin. This paper is a review of methods applied to identify individuals from natural and artificial sea trout spawning in rivers, and it proposes using genetic techniques as an alternative to traditional marking methods. A set of 13 microsatellite loci are proposed that are characterized by high selectivity. Using negative controls while simulating the assignment of parental pairs revealed that the number of loci in the set was highly significant and should not be reduced. This method could be useful in the proposed assessment of the proportions of wild and cultured fish in Polish rivers.

Bigger is Better: Optimizing Trout Stocking in Western Washington Lakes

AbstractThe effect of the length of Rainbow Trout Oncorhynchus mykiss on catch rate, catch size, and cost of stocking was evaluated in two western Washington lakes. Rainbow Trout of two general length‐classes (200–300 [“catchables”] and 300–400 mm [“jumbos”]) were differentially marked and stocked 1 d prior to a fishery utilizing typical sportfishing techniques. In both study lakes, larger trout represented a larger proportion of the total catch than would have been expected if proportional to lengths at stocking. Fish in the largest individual length‐class (360–380 mm) were, on average, 12.5 times more likely to be caught by sport anglers than those in the smallest individual length‐class (200–220 mm). Larger Rainbow Trout are more expensive to produce for stocking agencies. However, fish stocked in the 280–300‐mm class were twice as likely to return to the creel as expected and therefore are the best value in terms of number of fish caught per dollar invested. The results of this study suggest that a stocking strategy aimed at stocking fish 280 mm or larger would result in lower cost overall and increased satisfaction from anglers. Additionally, stocking Rainbow Trout less than 280 mm appears to have minimal recreational value in western Washington lakes.Received July 14, 2016; accepted January 7, 2017 Published online April 4, 2017

Nonnative fish stocking alters stream ecosystem nutrient dynamics.

Each year, millions of hatchery-raised fish are stocked into streams and rivers worldwide, yet the effects of hatchery-raised fish on stream nutrient cycles have seldom been examined. We quantified the influence of supplemental nonnative fish stocking, a widespread recreational fishery management practice, on in-stream nutrient storage and cycling. We predicted that supplemental, hatchery-raised brown trout (Salmo trutta) stocking would result in increased N and P supply relative to in-stream biotic demand for those nutrients and that stocked fishes would remineralize and store a significantly greater amount of N and P than the native fish community, due to higher areal biomass. To test these predictions, we measured the biomass, nutrient (NH4+ -N and soluble reactive phosphorus [SRP]) remineralization rates, and body carbon, nitrogen, and phosphorus content of the native fish community and trout stocked into four study streams. We then estimated fish growth rates to determine species-specific nutrient sequestration rates in body tissues for both stocked and native fish and measured ammonium and phosphorus uptake rates to determine the relative influence of net fish nutrient remineralization on stream nutrient cycles. When brown trout were stocked in these systems at density levels that were orders of magnitude higher than ambient native fish density, they provided a sizeable source of NH4+ -N that could account for up to 85% of demand for that nutrient. Stocked trout had minimal effects on in-stream SRP cycles even at high release densities, likely due to low per capita SRP excretion rates. A unique feature of our study was that we evaluated the temporal component of the stocked trout nutrient subsidy by estimating the number of fish removed from the system through natural mortality and angler harvest, which indicated that the stocked trout subsidy lasted approximately 6-8weeks after stocking. By combining population models with areal nutrient excretion rates and estimates of biotic nutrient uptake, we showed that trout stocking provided a strong pulsed nutrient subsidy.

Вплив згодовування плідникам райдужної форелі ганаміновіту на виживання заплідненої ікри та передличинок

The aim of research was a study the effect of influence of feeding by feed supplement of Ganaminovit the breeding stock of rainbow trout on the state of fertilized eggs and pre-larvae. The task of research was to study influence of Ganaminovit on the survival of fertilized eggs and on the productive effect of larvae in the conditions of the closed water-supply. The breeding stock of rainbow trout were fed by the extruded mixed fodders with Ganaminovit in 2015 during two months to and after spawning and in 2016 before spawning. The influence of feeding rainbow trout breeding stock, along with extruded feed vitamin supplements – Ganaminovit on the survival rate of fertilized eggs and pre-larvae for the mass of 0.3 g. It is established that in conditions of closed water system in the pre-spawning and after-spawning periods of the breeding stock of rainbow trout requires additional vitamin supplements, other than those included in the modern extruded food. The introduction supplements for two months, before incubation, promotes more rapid recovery of the body in after-spawning period and enhances immunity and high survival rates of eggs and of pre-larvae for the mass of 0.3 g. Mortality of eggs in the control group of breeding stock at the stage of the eye was 61.7%, and the increase of weight of the larvae during transition to active feeding in 2015–0,041 g. In 2016, these figures were higher and amounted to respectively 79.4% of and 0.052 g.