Stocked Rainbow Trout Research Articles

An Attempt to Rehabilitate a Collapsed Brook Trout Population by Introducing F1 Splake to Control Yellow Perch

AbstractHistorically, brook trout Salvelinus fontinalis provided an outstanding sport fishery and lived sympatrically with yellow perch Perca flavescens in East Lake, a 30‐ha water body in central Ontario. The fishery collapsed when lake access was improved and cottages were built around the shore in the early 1960s. Annual stocking of brook trout did not improve the brook trout fishery. During the 1980s it became apparent that yellow perch were abundant and small‐bodied. Based on historical studies in similar ecosystems, we concluded that the perch were competing directly with, and possibly preying on, the juvenile brook trout. In this study we attempted to reduce the perch population by repeatedly stocking first‐generation (F1) splake hybrids (female lake trout Salvelinus namaycush × male brook trout) over a 7‐year period. We hypothesized that the splake would reduce the abundance of yellow perch, which in turn would allow the brook trout population to increase. Stock assessments during the study period (1990–1997) indicated that the yellow perch density declined more than 95% (from approximately 3,400 to approximately 130 individuals/ha). We argue that the splake caused this reduction because routinely stocked rainbow trout Oncorhynchus mykiss and brook trout had failed to reduce the number of yellow perch and the decline coincided with the splake stocking. In addition, concurrent diet analyses indicated that splake were considerably more piscivorous and much more likely to consume yellow perch than were rainbow trout and brook trout. Although the number of yellow perch was greatly reduced, the brook trout population did not appear to increase; nor was there evidence of a decline in the absence of stocking during the manipulation. We propose the following reasons for the lack of a brook trout response: overharvesting, interspecific competition among salmonids or from residual forage species, the brevity of the study period, and genetic introgression with hatchery brook trout.

Otolith Chemistry Discriminates among Hatchery‐Reared and Tributary‐Spawned Salmonines in a Tailwater System

AbstractThe Little Red River tailwater (LRRT) system in Arkansas supports a naturally reproducing population of brown trout Salmo trutta and an economically valuable fishery. Natural reproduction by stocked brook trout Salvelinus fontinalis and rainbow trout Oncorhynchus mykiss is unknown but assumed to be negligible. An artificial tributary to the LRRT was constructed to provide a spawning and nursery refuge for stocked trouts, and shortly thereafter we observed spawning adults and emergent fry in the tributary. As a first step in determining the relative contributions of hatchery‐ and tributary‐produced brook and rainbow trouts recruiting to the LRRT fishery, we distinguished hatchery‐reared fry from tributary‐spawned fry via otolith chemistry. We used laser ablation inductively coupled plasma mass spectrometry to measure the abundances of cations in otoliths. Significant differences between hatchery and wild stocks were found for six element : Ca ratios. A five‐variable (Mg, Mn, Zn, Sr, and Ba) discriminant model was sufficient to distinguish the two brook trout stocks with 100% accuracy, and a two‐variable (Sr and Ba) model discriminated between the two rainbow trout stocks with 94% accuracy. Differences in ambient water chemistry between the two rearing habitats most likely accounted for these distinct otolith signatures. Otolith analysis of brook trout parr of unknown origin captured in the LRRT system suggests that natural reproduction is occurring there and that this stock may be supplemented with tributary‐spawned immigrants. After interannual variation in habitat‐specific otolith chemical signatures is quantified, such an analytical tool would be useful to managers in the LRRT system and elsewhere in determining the relative contributions of various stocks to reproductive and harvested populations.

Relationships among growth and different NOR phenotypes in a specific stock of rainbow trout (Oncorhynchus mykiss)

Growth is one of the most important aspects in the genetic improvement of cultured fish species. Consequently, genetic parameters related to this feature and their response to selection have been the focus of most research in this area. Such research indicates that, in general, there is enough additive genetic variance related to growth, justifying the use of selection. Based on the usefulness of cytogenetic and molecular markers in the fish culture, the aim of the present work was to analyze the possible relationships among cytogenetic characteristics, specifically the NOR phenotypes, and the increase in length and weight in specimens of the rainbow trout (Oncorhynchus mykiss), resultant from directed mating between homozygous females and heterozygous males according to their NOR phenotypic patterns. The equations of the relationship between length and weight of the analyzed specimens followed the model Wt = a Lt(b), showing b values higher than 3, determinant of a positive allometric growth. The results showed that the different NOR phenotypes were not related with the growth values for length and weight in any statistical test.

Nonnative brook trout (Salvelinus fontinalis) and the demise of native brown trout (Salmo trutta) in northern boreal lakes: stealthy, long-term patterns?

This study of 193 boreal lakes of northern Sweden suggests a long-term detrimental impact of introduced brook trout (Salvelinus fontinalis) on brown trout (Salmo trutta) populations. Thirteen of 65 (20%) brown trout populations in lakes exposed to brook trout went extinct, whereas the extinction rate in unexposed lakes was significantly lower (2%). We verified other studies that indicate that altitude strongly affects the distribution of the two species; brown trout populations in our higher altitude lakes were more sensitive to impact from brook trout. In 28 lakes above 285 m, 12 trout populations exposed to brook trout went extinct, while only one population became extinct in 37 lakes below 285 m. No effects of other environmental factors were detected (e.g., water chemistry, stocking of rainbow trout (Oncorhynchus mykiss), fish species community assembly, migration barriers, or lake morphometry on brown trout extinction). The time lag between the first record of brook trout introduction and subsequent extinction of brown trout was two decades on average (maximum 70 years). Even though further stocking of brook trout has been stopped, our analysis suggest that existing sympatric populations may continue to pose an extinction threat to brown trout.

Virulence Comparisons of Infectious Hematopoietic Necrosis Virus U and M Genogroups in Sockeye Salmon and Rainbow Trout.

Infectious hematopoietic necrosis virus (IHNV) is an aquatic rhabdovirus that infects salmonids in the Pacific Northwest of the United States, Europe, and Asia. Isolates of IHNV have been phylogenetically classified into three major viral genogroups, designated U, M, and L. To characterize virulence of IHNV in the context of these three viral genogroups, seven strains of IHNV (three U genogroup strains, three M strains, and one L strain) were compared for their pathogenicity in juvenile sockeye salmon Oncorhynchus nerka, kokanee (lacustrine sockeye salmon), and rainbow trout O. mykiss. Fish were waterborne-exposed to the different viral strains, and virulence was assessed by comparing mortality curves and final cumulative percent mortality (CPM) in both species of fish at 10°C and 15°C. In sockeye salmon and kokanee, the U genogroup virus types were extremely virulent, causing average CPMs of 69-100%, while the M genogroup virus types caused very little or no mortality (CPM = 0-4%). The endangered Redfish Lake sockeye salmon stock exhibited extreme differences in susceptibility to the U and M genogroups. Conversely, in two stocks of rainbow trout, the M genogroup virus types were more virulent, inducing average CPMs of 25-85%, while the U genogroup viruses caused lower mortality (CPM = 5-41%). In both fish species, the single L genogroup strain caused low to intermediate mortality (CPM = 13-53%). Viral glycoprotein sequence comparisons of the seven challenge strains revealed three amino acid sites (247, 256, and 270) that consistently differed between the U and M genogroups, possibly contributing to pathogenicity differences.

Genetic Diversity among Hatchery Stocks and Established Populations of Rainbow Trout in Missouri

AbstractIntroduction of rainbow trout Oncorhynchus mykiss in Missouri over the last 125 years has established numerous self‐sustaining populations. While many populations have been repeatedly stocked, some have received few fish beyond the original releases, and it is possible that those populations currently represent their source lineages. There is angler interest in fishing “wild” rainbow trout populations both for historical purposes and for the fighting ability of hooked fish. A genetic inventory was conducted to determine the extent to which Missouri's wild fish differ from hatchery stocks. Haplotype diversity in the mitochondrial DNA (mtDNA) cytochrome b gene and allele frequencies at four microsatellite loci were examined. Significant differences in mtDNA genotypes were found among several wild and hatchery sources, indicating that multiple sources of rainbow trout were probably represented. Crane Creek—long considered a stronghold of McCloud River (California) redband trout O. mykiss stonei in Missouri—and its tributary, Spring Creek, were characterized as having a large proportion of unique haplotypes. Microsatellite diversity was largely shared among individuals within populations, and average heterozygosity was high. By including this information in decisions about regulations and stocking, the Missouri Department of Conservation can manage rainbow trout to satisfy angler interests with respect to both historical and performance‐related population characteristics.

Factors That Limit Growth and Abundance of Rainbow Trout across Ecologically Distinct Areas of Flaming Gorge Reservoir, Utah–Wyoming

AbstractRainbow trout Oncorhynchus mykiss stocked into Flaming Gorge Reservoir, Utah– Wyoming, are thought to be in poor condition and to rarely overwinter. In 2001–2002, we evaluated factors that affect the growth and abundance of rainbow trout, both temporally and spatially, based on a series of field measurements and growth experiments. Based on our field measurements, the growth and condition of rainbow trout in Flaming Gorge Reservoir actually parallel those of rainbow trout of various strains in other systems, and some rainbow trout overwinter as many as 3 years in the reservoir. Overall, rainbow trout appear to be spatially limited by physical factors (e.g., temperature) during only a few isolated times of the year and not in all areas of the reservoir. Although zooplankton were abundant throughout the reservoir, primary and secondary production vary spatially with concordant effects on fish growth and condition. Diet analysis indicated that rainbow trout consume primarily aquatic macroinvertebrates along with some zooplankton and demonstrate an extremely limited switch to piscivory at larger sizes. Rainbow trout reared in net‐pens and limited to a diet of zooplankton lost weight in all three areas of the reservoir. In addition, the reservoir supports a large population of trophy lake trout Salvelinus namaycush, which probably affects the abundance of rainbow trout directly through consumption and the growth potential of rainbow trout indirectly through risk‐averse behavior. The combination of spatial variation in reservoir productivity and habitat type, differing stocking strategies, and behavioral responses caused by predators appears to determine the varying success of stocked rainbow trout in the different areas of the reservoir. Our study suggests that stocking strategies may be most effective when specific characteristics of the prey and predator base, the suitability of different habitats, and the genetic strain are explicitly evaluated within the context of the targeted angler population.

Anchor and Visible Implant Elastomer Tag Retention by Hatchery Rainbow Trout Stocked into an Ozark Stream

As part of a study to evaluate the stocking of rainbow trout Oncorhynchus mykiss in an Oklahoma Ozark stream, we tagged 2,542 hatchery-reared rainbow trout (123–366 mm total length) with individually numbered Floy FD-68B anchor tags and visible implant fluorescent elastomer (VIE) tags. We experimentally stocked double-marked rainbow trout into a small northeastern Oklahoma stream from November 2001 to March 2002 and resampled them monthly from December 2001 to October 2002 by electrofishing. Anchor tag retention was 91% through 6 months, and VIE tag retention was 96% through 6 months despite extensive handling of fish within 24 h of tagging. Based on the ease of application, high visibility, and high retention observed in this study, we recommend the use of VIE tags as a batch mark in similarly sized, similarly pigmented fish. The retention of VIE tags was slightly higher than that of anchor tags, and cost per fish was less for VIE than for anchor tags. However, VIE tags would have limited utility if numerous individual tags are necessary; therefore, we recommend anchor tags as individual marks in similarly sized salmonids. Retention for both tag types was relatively high and could be corrected for when estimating population parameters from tagging data.

Differing Resistance of Atlantic Salmon Strains and Rainbow Trout to Gyrodactylus salaris Infection

AbstractLaboratory studies were conducted on the susceptibility of different strains of Atlantic salmon Salmo salar and rainbow trout Oncorhynchus mykiss to infection with the monogenean Gyrodactylus salaris. This parasite, probably originating from the Baltic Sea region, is known to minimally affect Neva River (Baltic Sea) Atlantic salmon. However, following its introduction into Norway, G. salaris has caused severe mortality and morbidity among Norwegian Atlantic salmon, which are considered a highly susceptible strain. The cohabitation experiment included one stock of rainbow trout and four different strains of Atlantic salmon from the Baltic Sea region (Mörrum River, Sweden), Europe (Skjern River, Denmark; Conon River, Scotland), and North America (Bristol Cove River, Canada). Fish were exposed to a Norwegian strain of G. salaris, and parasite population development and distribution were monitored for 7 weeks. Rainbow trout exhibited low susceptibility to G. salaris infection, whereas Conon River and Skjern River Atlantic salmon were highly susceptible and exhibited high mortality rates. Mörrum River Atlantic salmon exhibited intermediate susceptibility and low mortality. Bristol Cove River Atlantic salmon harbored relatively low parasite numbers, but fish mortality was high. Our experiment showed that the Danish Skjern River strain of Atlantic salmon is highly susceptible to G. salaris infection, further supporting the hypothesis that Atlantic Ocean strains are more susceptible to G. salaris infection than are Baltic strains.

Evaluation of Three Gears for Sampling Spawning Populations of Rainbow Trout in a Large Alaskan River

AbstractAlternatives to electrofishing are needed for sampling sexually mature rainbow trout Oncorhynchus mykiss during the spawning season in large Alaskan rivers. We compared hook and line, beach seining, and actively fished gill nets as sampling tools. Beach seining and active gill netting yielded similar catch rates, length frequencies, and sex ratios of sexually mature fish. Hook‐and‐line sampling was less effective, with a lower catch rate and selectivity for immature fish and sexually mature females. We conclude that both beach seining and active gill netting can serve as alternatives to electrofishing for sampling sexually mature rainbow trout stocks during the spawning season in large rivers with stable spring flows and spawning areas with few snags.

The origin of introduced rainbow trout (Oncorhynchus mykiss) in the Santa Cruz River, Patagonia, Argentina, as inferred from mitochondrial DNA

Rainbow trout (Oncorhynchus mykiss) was first introduced into Argentinean Patagonia, the southernmost region of South America, from the United States in 1904 and at present constitutes the most conspicuous freshwater fish in lakes and rivers of the region. The Santa Cruz River in Southern Patagonia is the only river in the world where a self-sustained population of introduced rainbow trout is known to have developed an anadromous run. In this study, we examined mtDNA sequence variation to identify the source of Santa Cruz River rainbow trout, providing a historical framework to interpret the processes underlying phenotypic variation and structure of Patagonian populations. The Santa Cruz River may harbor distinct North American stocks of rainbow trout, widely distributed around the world during the late 19th and early 20th centuries, but today threatened after decades of habitat loss, species introduction, and introgression from alien stocks. The mtDNA sequence data revealed that the most likely origin for wild anadromous and nonanadromous fish was the McCloud River in California. Meanwhile, a local hatchery stock, representative of rainbow trout introduced from Denmark after 1950 and widely stocked ever since throughout Patagonia, most probably originated from multiple lineages from western North America, including non-Californian populations.

Great Blue Heron Predation on Stocked Rainbow Trout in an Arkansas Tailwater Fishery

Abstract Fisheries managers seldom have adequate information to assess their stock losses to avian piscivores, which function as apex predators in many aquatic food webs. Our primary objective was to estimate the number of stocked rainbow trout Oncorhynchus mykiss consumed by great blue herons Ardea herodias on the Bull Shoals and Norfork tailwaters of north-central Arkansas. Between November 2000 and December 2001, we periodically surveyed great blue herons along 150.7 river km on the tailwaters of the Bull Shoals and Norfork dams. Heron density (number/km) in or along the river ranged from 0 to 4/km per survey, with the highest mean number located near the Bull Shoals Dam (2.31 herons/km). We recorded 467 prey captures by herons during 202 observation hours. Sculpin Cottus spp. were the most common prey (N = 120). Most prey (87%) measured 14 cm or less in length, and most captured live trout (85.4%) fell between 10.5 and 28.0 cm in length. While live trout represented only 48 of 359 identifiable prey it...

Electrofishing Injury and Short-Term Mortality in Hatchery-Reared Rainbow Trout Stocked into an Ozark Stream

Abstract We conducted an electrofishing injury study to evaluate potential effects of sampling procedures on survival and health of hatchery rainbow trout Oncorhynchus mykiss (187–307 mm total length) stocked into an Ozark stream. We assessed two groups of trout: one group had acclimated to stream conditions for 1 month; the other group was handled and transported just before the study. Each group was sampled by electrofishing (boat-mounted, 60-Hz AC) and seining (controls), resulting in four treatment groups (N = 21). We held fish for 48 h to evaluate mortalities in that period, then euthanized all fish and examined them for hemorrhages and spinal damage. No fish died during the 48-h holding period, indicating that our procedures did not cause significant sampling-related mortality among stocked trout in Brush Creek. Spinal damage was observed in 5% of fish collected with electrofishing but in none of the control fish. We found hemorrhages in 90% of electrofished trout but none in control fish, and recen...

Chromosome Localization of the Ribosomal Genes 18S and 5S in Four Stocks of Rainbow Trout (Oncorhynchus mykiss) from Cultivated and Naturalized Stocks in Brazil

In the present study, fluorescence in situ hybridization (FISH) was employed to determine the chromosomal location of genes 18S rDNA and 5S rDNA in four rainbow trout stocks. In specimens from the stocks of Nucleo Experimental de Salmonicultura de Campos do Jordao and Gaviao river, 18S genes were located at a subterminal position in the long arms of two submetacentric chromosomes, whereas in specimens from stocks of Mount Shasta and Teresopolis they were found in the short arms. In all analyzed stocks, 5S genes were located in two chromosome pairs. In a subtelocentric pair, 5S genes were present in the short arms and, in the other submetacentric pair, 5S genes were at an interstitial position. In the latter, 18S and 5S genes were contiguous. Taking into account that both 18S and 5S rDNA genes have been localized in the short arm of a submetacentric chromosome in almost all rainbow trout samples so far studied, the presence of such genes in the long arm, as seen in the samples from Nucleo Experimental de Salmonicultura de Campos do Jordao and Gaviao river, supports the hypothesis of a pericentric inversion involving this chromosome segment in the ancestor line of these stocks. The observed polymorphism allowed the identification of a very useful genomic marker, and may therefore constitute an important tool in the genetic management of rainbow trout stocks.

Characteristics of Smallmouth Bass (Micropterus dolomieu) and Shadow Bass (Ambloplites ariommus) Populations in an Ozark Stream before and after Rainbow Trout Introduction

ABSTRACT We evaluated characteristics of smallmouth bass (Micropterus dolomieu) and shadow bass (Ambloplites ariommus) populations in a small, northeastern Oklahoma Ozark stream from February 2000 to March 2003 to evaluate potential effects of rainbow trout (Oncorhynchus mykiss) introduction on these species. We experimentally stocked rainbow trout into the stream from November 2000 to March 2001 and November 2001 to March 2002. Mark-recapture and telemetry data showed patterns of limited movement among pool habitats by both bass species, and presence of rainbow trout in Brush Creek did not appear to influence movement patterns. We documented recruitment by smallmouth and shadow bass during our study, indicating that rainbow trout introduction did not inhibit spawning. Mean relative weight (W,r) of smallmouth bass ranged from 77—80, and we did not detect differences in relative weight among pre-stocking, the first year of stocking, and the second year of stocking. It appears that important population characteristics of these two species in our study stream were not negatively impacted by rainbow trout introduction.

A lethal effect associated with polymorphism of the NOR-bearing chromosomes in rainbow trout (Oncorhynchus mykiss)

Cytogenetic analysis of a rainbow trout stock showed that the nucleolar organizing regions were located subterminally on the long arm of a submetacentric chromosome pair and occurred as a single chromosomal segment (phenotype N1) or as two chromosomal segments separated by a short euchromatic segment (phenotype N2). Cytogenetic analysis also showed that there were N1N1 and N1N2 individuals but no N2N2 individuals. Analysis of the different includedphenotypes incluted that the population was not in Hardy-Weinberg equilibrium (chi² = 19.333; p < 0.01), and that a higher frequency of individuals had the N1N2 phenotype. Experimental crosses involving four males (two N1N1 and two N1N2) and four females (one N1N1 and three N1N2) yielded eight broods. There were no significant differences between the expected and observed frequencies of offspring resulting from crosses involving N1N1 x N1N2 individuals. However, significant differences were seen in crosses involving N1N2 x N1N2 parents because of the a high incidence of N1N2 fishes and the absense of N2N2. The lack of N2N2 individuals in the parental sample and their absence among the offspring of the experimental crosses suggested that this genetic combination may be lethal in rainbow trout. The survival rates of embryonic "eyed egg" and fry stage individuals were not different, indicating that the possible lethal effect may occur during more advanced ontogenetic phases.

Erosion of interspecific reproductive barriers resulting from hatchery supplementation of rainbow trout sympatric with cutthroat trout

The frequency of hybridization between cutthroat (Onchorhynchus clarki clarki) and rainbow (O. mykiss irideus) trout from coastal habitats in British Columbia, Canada, was examined in seven populations where the two species are sympatric with no history of rainbow trout stocking and compared with areas where native rainbow trout populations have been supplemented with hatchery fish (three populations). Four nuclear markers were used to identify each species and interspecific hybrids and one mitochondrial marker showed the direction of gene exchange between species. The frequency of hybrids was significantly higher (Fisher exact test, P < 0.001) in river systems where hatchery rainbow trout have been introduced (50.6% hybrids) than in populations where the two species naturally co-occur without supplementation (9.9% hybrids).

NORs inheritance analysis in crossings including individuals from two stocks of rainbow trout (Oncorhynchus mykiss).

Silver nitrate staining of rainbow trouts (Oncorhynchus mykiss) chromosomes, for the identification of the nucleolar organizing regions (NORs), revealed that in individuals from Núcleo Experimental de Salmonicultura de Campos do Jordão (Brazil) NORs were located in the long arms of submetacentric pair while in specimens from Mount Shasta (USA) NORs were located in the short arms of a submetacentric pair. Cytogenetic analysis of the offspring, obtained through artificial crosses including individuals from both stocks, allowed the identification of NORs in two submetacentric chromosomes, one in the short arms and the other in the long arms, confirming the effectiveness of the hybridization process. Complementary results obtained using the FISH technique with 18S and 5S rDNA probes showed that NOR-bearing chromosomes exhibited a cluster of 5S genes located in tandem with the 18S gene cluster in both stocks. The results allow us to suggest that the difference in NOR-bearing chromosomes found between the two stocks is likely to be due to pericentric inversion involving the chromosome segment where 18S and 5S rDNA genes are located. The presence of ribosomal genes in the long arms of a submetacentric chromosome is apparently a particular characteristic of the rainbow trout stock of Campos do Jordão and might be used as a chromosome marker in studies of controlled crosses in this species.

Fate, Dispersal, and Persistence of Recently Stocked and Resident Rainbow Trout in a Tennessee Tailwater

A popular trout fishery in the Clinch River below Norris Dam, Tennessee, is maintained by an extensive stocking program. However, survival and return rates of rainbow trout Oncorhynchus mykiss stocked as catchables are low. Twenty rainbow trout (mean total length (TL) = 307 mm) that had resided in the tailwater at least 5 months were collected from the river and implanted with radio transmitters in June 1998. Similarly sized rainbow trout were implanted with radio transmitters at a hatchery and stocked into the Clinch River on 8 July 1998 (N = 19; mean TL = 304 mm) and 16 September 1998 (N = 11; mean TL = 311 mm). The stocked rainbow trout dispersed rapidly and nearly all (93%) of those fish died quickly or emigrated from the tailrace. Resident fish were significantly less active than stocked fish, and they persisted significantly longer (Kruskal–Wallis tests, P = 0.0001). Poor return rates and survival of rainbow trout stocked as catchables were attributed to their rapid, long-range movements and high levels of activity. Such behaviors are energetically inefficient and probably rendered them more vulnerable to predation.

Androgenesis in rainbow trout using cryopreserved spermatozoa: the effect of processing and biological factors

In addition to producing homozygous lines for biomedical and genomic research and monosex stocks for commercial purposes, androgenesis is the biotechnology considered most promising and reliable for recovering complete nuclear genome information from cryopreserved fish cells. That is because procedures of cryopreserving spermatozoa, contrary to procedures for oocytes or entire eggs, are being well developed. Application of androgenesis in genome banking programs addresses the needs of both the aquaculture industry (safeguard for valuable strains and lines) and natural resource conservation (in vitro protection of endangered species or populations). The present study was focused on successful production of an androgenetic rainbow trout stock using cryopreserved spermatozoa. Our report constitutes the first time a full factorial analysis of processing and biological factors affecting androgenesis efficacy has been presented. Also for the first time, the survival of androgenetic individuals during 2 years of life was recorded. Remarkably high survival rates were observed in one of the two experiments—up to 42.5±2.8% of hatched larvae, 22.5±0.1% of swim-up larvae and 10.5% of androgenetic alevins 0.4 g. Mortality rates in androgenetic groups were high especially during the first 6 months. In all, 114 androgenetic individuals (0.9%) survived 2 years. Cryopreservation of spermatozoa generally did not affect androgenesis efficiency significantly, however, this effect was significantly dependent on the method of ploidization shock and on the duration of treatment. Significant interactions were revealed between the irradiation dose and the magnitude of pressure applied, and between the treatment of sperm and duration of pressure shock. Individual variability of spermatozoa donors significantly affected androgenesis efficiency regardless of their genetic (outbred or inbred) origin. Genetic source of the oocytes, contrary to spermatozoa, proved to be an important factor. Following findings of other researchers that androgenesis using cryopreserved spermatozoa is possible, we demonstrated that viable stock could be successfully established from cryopreserved nuclear genome information. Complex statistical analysis of previously developed procedures resulted in information-rich data regarding factorial interactions helpful for developing protocols in genome-restoration programs.