Paul D. Scheerer

Androgenetic rainbow trout produced from inbred and outbred sperm sources show similar survival

Abstract Androgenesis is a technique that could facilitate the rapid production of completely homozygous isogenic lines of fish. We induced diploid androgenesis in rainbow trout (Salmo gairdneri) by fertilizing 60Co gamma-irradiated eggs with untreated sperm and then blocking the first cleavage division with hydrostatic pressure. Electrophoresis of enzymes encoded by seven loci confirmed the complete homozygosity and all-paternal inheritance of the androgenetic progeny. We used sperm from both inbred and outbred strains to determine if the survival of androgens was greater with sperm from inbred males because of a reduction in the number of deleterious recessive alleles in inbred strains. Survival of androgenetic diploids from inbred and outbred sperm sources was similar and significantly below that of outbred controls. The similar survival of androgens from inbred and outbred sperm sources may be the result of high treatment mortality associated with androgenesis.

Androgenetic rainbow trout produced using sperm from tetraploid males show improved survival

Abstract Androgenesis is a technique which involves the production of individual with all their chromosomes from the male parent. It can be useful in generating homozygous lines of fish and in the recovery of genotypes from cryopreserved sperm. However, the survival of androgenetic diploid fish is typically very low; this may be due to the homozygosity of these individuals or to the treatments (egg irradiation, suppression of first cleavage) used in generating them. In this study, we produced androgenetic diploid rainbow trout using (1) normal (haploid) sperm and suppression of the first cleavage, and (2) sperm from tetraploid males. Survival of the androgenetic diploids generated using sperm from tetraploid males was much better than that of androgenetic diploids produced using haploid sperm, suggesting that egg irradiation is not an overwhelming problem in androgenesis and that cleavage suppression treatments and/or homozygosity may be responsible for their poor viability. We also generated viable androgenetic diploids using cryopreserved sperm from tetraploid males; this technique may be useful for gene banking.

Residual paternal inheritance in gynogenetic rainbow trout: implications for gene transfer.

SummaryPollen irradiation has recently been widely investigated as a method for differential gene transfer in plants. Using an albino color marker in rainbow trout (Salmo gairdneri), we have investigated whether irradiated sperm might be used in an analogous manner for gene transfer in fish. Our results indicate that paternal chromosome fragments are genetically active in gynogenetic offspring, but that these fragments may be lost during mitotic cell division, producing mosaic fish.

Increased resistance of triploid rainbow trout × coho salmon hybrids to infectious hematopoietic necrosis virus

Abstract Diploid and heat-induced triploid treatment groups of rainbow trout ( Salmo gairdneri ), coho salmon ( Oncorhynchus kisutch ), and reciprocal hybrid crosses were produced and monitored for survival and growth through early life stages. Survival to the fry stage showed a significant increase in the triploid rainbow trout female × coho salmon male hybrids relative to the diploid hybrid group. At a mean weight of 0.65 g all groups were administered a standardized static bath challenge with Leong Type 2 virulent IHN virus. The triploid rainbow trout female × coho salmon male hybrids showed a significant increase in IHN resistance when compared to pure-species rainbow trout groups. Early growth results suggest a poorer growth rate for the triploid hybrid. Triploid hybridization improved viability of the hybrid cross, increased relative resistance to IHN virus challenge, and may provide a useful method for the interspecific transfer of desired characters into commercial fish stocks.

Improved Fertilization by Cryopreserved Rainbow Trout Semen Treated with Theophylline

Abstract The fertilizing capacity of cryopreserved semen of rainbow trout (Oncorhynchus mykiss) was improved when eggs were fertilized in a buffered saline activator solution containing 5 mM theophylline, a caffeine relative that prolongs and intensifies sperm motility.

Implications of Floodplain Isolation and Connectivity on the Conservation of an Endangered Minnow, Oregon Chub, in the Willamette River, Oregon

Abstract The objectives of this study were to determine the distribution and abundance of endangered Oregon chub Oregonichthys crameri, a small floodplain minnow endemic to the Willamette Valley of western Oregon; to describe the fish communities in current and historic chub habitats; and to establish new populations through introductions. Various sampling gears were used, including seines, minnow traps, dip nets, and a gill net. Oregon chub distribution was found to be restricted in comparison with their historical range, whereas nonnative fishes were widespread in the off-channel habitats preferred by Oregon chub. Oregon chub were absent, or low in abundance, when nonnative fishes were present, and several populations declined or were extirpated when their habitats were invaded by nonnative fishes. Isolated habitats with low connectivity supported larger populations of Oregon chub and were less likely to contain nonnative fish species than were habitats with high connectivity. In habitats that supported...

Incidence of albinos as a monitor for induced triploidy in rainbow trout

Abstract Albinism is a recessive trait in rainbow trout ( Oncorhynchus mykiss ). We tested for complementation at the albino locus among six USA rainbow trout strains and found that albinos from four domesticated strains and one Idaho steelhead strain are mutant at the same locus. These strains apparently are tyrosinase-deficient albinos. An albino steelhead strain from Washington State and an albino brook trout ( Salvelinus fontinalis ) strain are apparently mutant at other loci because they produce pigmented progeny when crossed to the common form of albino rainbow trout. We determined using gynogenesis that the albino locus common in domesticated rainbow trout maps very near the end of a chromosome; virtually all the gynogenetic progeny of heterozygous females were pigmented. In contrast, the Golden locus of rainbow trout appears centromere-linked. Female rainbow trout heterozygous for the albino gene have 50% albino offspring when crossed to albino males but a high proportion of pigmented offspring after a heat shock is applied to induce triploidy. The proportion of pigmented offspring would be expected to correlate directly to the proportion of triploid individuals in such crosses. However, pigmented diploids can sometimes be found in such crosses in higher than predicted frequencies, apparently because heat shock can sometimes induce rejection of the sperm. This indicates that diploids observed among lots treated to induce triploidy may result from sperm rejection as well as from failure of second polar body retention.

Population Dynamics and Stock Differentiation of Lake Whitefish in Northeastern Lake Michigan with Implications for their Management

Abstract Lake whitefish (Coregonus clupeaformis) were tagged and the commercial trap-net catch was sampled in northeastern Lake Michigan to differentiate discrete stocks and determine their vital statistics. Distribution of tag returns and statistical comparisons of certain population parameters suggested the existence of at least three discrete stocks in the study area. The stock inhabiting the North Shore area of eastern Lake Michigan was considerably larger in both numbers and biomass than the stock fished near Leland, Michigan. The Leland catch had a broader age composition and contained larger fish than the North Shore and Beaver Island samples. Exploitation and total mortality rates were similar in the North Shore and in the Leland fisheries. The more abundant North Shore stock showed slower back-calculated and instantaneous growth than the Leland stock. In terms of management, statistics of abundance, growth, and mortality clearly varied between different lake whitefish stocks within Lake Michigan,...

Comparison of three methods for marking a small floodplain minnow

BackgroundEvaluation of the movement patterns of small-bodied fish is often hindered by the lack of a suitable long-term mark. We evaluated several techniques for long-term group and individual identification of adult (40–70 mm total length [TL]) Oregon chub (Oregonichthys crameri). We marked Oregon chub with one of two different sized passive integrated transponder (PIT) tags (a 9 × 2.12 mm, 0.067 g PIT tag [PIT-tag] or a 8.4 × 1.4 mm, 0.033 g PIT tag [PICO-tag]), a red visible implant elastomer (VIE) tag, or a freeze brand. We monitored survival, tag retention, and mark quality over 150 days. In addition, we assessed the minimum length and weight thresholds to achieve 80% and 90% survival of PIT-tagged fish.ResultsMarking with a freeze brand, PICO-tag, or VIE tag had no effect on survival (P >0.05). In contrast, marking with a PIT-tag was associated with significantly lower (P <0.05) survival than in the control group. Survival was significantly higher (P = 0.002) for fish implanted with a PICO-tag than with the larger PIT-tag.The initial minimum TL for 80% and 90% survival was 54 mm and 64 mm TL, respectively, for the PIT-tag treatment. The 90% survival threshold for PICO-tagged fish was 44 mm TL. The 80% survival threshold was outside the range of sizes used in our experiment (<40 mm TL). Similarly, the 80% and 90% survival weight thresholds for the PIT-tag treatment were 1.5 g and 2.4 g, respectively, and the 90% survival threshold for PICO-tagged fish was 0.9 g.Tag retention was 94% and 95% in the PIT-tag and PICO-tag treatments, respectively; 80% of the freeze branded fish had easily recognizable tags after 150 days and 88% of the fish marked with VIE had easily recognizable tags after 150 days.ConclusionsPICO-tags, VIE marks, and freeze brands are all feasible long-term marking techniques for Oregon chub with negligible effects on survival through 150 days. The selection of a particular technique should be based on the study design and objectives (e.g., individual versus group identification), cost, ease, speed of tagging, and survival.

Analyses of Genetic Variation in Populations of Oregon Chub, a Threatened Floodplain Minnow in a Highly Altered Environment

Abstract The Oregon chub Oregonichthys crameri is a small floodplain minnow endemic to the Willamette River basin of western Oregon. Historically the species was widely abundant and probably relied on periodic floods for dispersal and genetic exchange among populations. The species has declined substantially in the past 100 years due to habitat alterations and the introduction of nonnative species and is currently listed as threatened under the U.S. Endangered Species Act. Information on the level of genetic variation within and among populations did not exist when the species was listed or when a recovery plan was being developed. In this study, we used a suite of nine microsatellite loci to characterize genetic variation within and among 16 sampling locations and provide information to help guide future recovery efforts. Even though many locations are presently isolated from one another, we observed relatively high levels of genetic variation within collections. Temporal samples revealed that the levels...