Native Rainbow Trout Research Articles

Lower fitness of hatchery and hybrid rainbow trout compared to naturalized populations in Lake Superior tributaries.

We have documented an early life survival advantage by naturalized populations of anadromous rainbow trout Oncorhynchus mykiss over a more recently introduced hatchery population and outbreeding depression resulting from interbreeding between the two strains. We tested the hypothesis that offspring of naturalized and hatchery trout, and reciprocal hybrid crosses, survive equally from fry to age 1+ in isolated reaches of Lake Superior tributary streams in Minnesota. Over the first summer, offspring of naturalized females had significantly greater survival than offspring of hatchery females in three of four comparisons (two streams and 2 years of stocking). Having an entire naturalized genome, not just a naturalized mother, was important for survival over the first winter. Naturalized offspring outperformed all others in survival to age 1+ and hybrids had reduced, but intermediate, survival relative to the two pure crosses. Averaging over years and streams, survival relative to naturalized offspring was 0.59 for hybrids with naturalized females, 0.37 for the reciprocal hybrids, and 0.21 for hatchery offspring. Our results indicate that naturalized rainbow trout are better adapted to the conditions of Minnesota's tributaries to Lake Superior so that they outperform the hatchery-propagated strain in the same manner that many native populations of salmonids outperform hatchery or transplanted fish. Continued stocking of the hatchery fish may conflict with a management goal of sustaining the naturalized populations.

Information from Radio Telemetry on movements and exploitation of naturalized Rainbow trout, Oncorhynchus mykiss (Walbaum), in Kenya cold water streams

Information from Radio Telemetry on movements and exploitation of naturalized Rainbow trout, <i>Oncorhynchus mykiss</i> (Walbaum), in Kenya cold water streams

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).

Mitochondrial and nuclear DNA sequence variability among populations of rainbow trout (Oncorhynchus mykiss)

Mitochondrial and nuclear DNA variability was examined to assess population genetic structure and phylogeographic relationships in rainbow trout. Single-strand conformation polymorphisms and restriction site differences within 1055 bp of the mitochondrial D-loop region and 1566 bp of nuclear DNA in six single-copy nuclear DNA regions identified 31 mitochondrial genotypes and 50 nuclear alleles. Gene trees were constructed by sequencing each variant allele or mitochondrial genotype identified. Examination of 30 populations in 10 native rainbow trout groups using analysis of molecular variance (AMOVA) indicated that 65% of mitochondrial variability and 35% of nuclear variability was explained by differences among the 10 groups. Phylogenetic patterns evident in mitochondrial and nuclear DNA were not always concordant. Differences in the evolutionary patterns detected by mitochondrial and nuclear DNA may reflect the differential impact of past introgression events on variability in the two genomes.

Genetic Variation in Naturalized Rainbow Trout ( Oncorhynchus mykiss) from Minnesota Tributaries to Lake Superior

Genetic variation at 27 polymorphic loci that code allozymes was compared among collections of naturalized, anadromous-form rainbow trout ( Oncorhynchus mykiss) from Lake Superior tributaries in Minnesota and among four hatchery strains. Genetic differences were observed among collections from naturalized populations from tributary streams and among hatchery strains (P < 0.01). In naturalized populations, most genetic variation observed occurred among individuals within samples (95.5%) and was comparable to values reported for other naturalized Lake Superior populations of rainbow trout. Cluster analysis of genetic distance coefficients revealed two main groups. One group included a subgroup of samples from heavily stocked streams (Devil Track, Flute Reed, and Baptism rivers) and the Michigan hatchery strain which had been used to stock these streams. The second group included collections from the Knife River drainage and Knife River hatchery fish. Collections from Indian Camp Creek and of the “kam-loops” hatchery strain were the most differentiated of the samples and showed little genetic affinity to each other or the two main groups. The “kamloops” strain did not exhibit allelic frequencies expected for rainbow trout derived from the Kamloops region of the upper Fraser River of British Columbia. No evidence was found to support the contention that the “kamloops” hatchery strain had interbred with wild populations. Widespread stocking of Michigan strain fish may have reduced genetic differences among naturalized, wild populations along Minnesota's Lake Superior shoreline. Population-specific management of rainbow trout by tributary is a justifiable approach to consider. If maintenance of the genetic differences among the wild, naturalized populations is desired, “kamloops” and the Michigan hatchery strains should not be stocked. Stocking programs instead should use gametes from returning adults of a river for subsequent juvenile propagation and stocking back into the same river.

A C-Terminal Fragment of the Hormone Stanniocalcin Is Bioactive in Eels

An in vivo eel bioassay based on 45Ca uptake from the ambient medium was used to compare the activity of native trout and American eel stanniocalcin (STC) with that of a synthetic C-terminal fragment (AA 202-231; peptide W) of Australian eel STC. Qualitatively, the action of peptide W resembled that of purified native rainbow trout ( Oncorhynchus mykiss) STC as well as fresh extracts of American eel Stannius corpuscles in that they all inhibited whole animal Ca 2+ influx. This inhibition was observed in both intact and stanniectomized eels regardless of whether the eels were exhibiting high or low initial calcium uptake rates. These observations suggest that peptide W activates eel gill STC receptors. Further, as peptide W was previously reported to stimulate Ca 2+ influx in intact rainbow trout fry, the present data provides evidence for a difference in the way this fragment functions in various species.

Genetic Comparison of Naturalized Rainbow Trout Populations among Lake Superior Tributaries: Differentiation Based on Allozyme Data

Allelic frequencies at 27 polymorphic allozyme loci were compared among 15 col- lections of naturalized migratory rainbow trout Salmo gairdneri sampled from 10 stream drainages leading to Lake Superior. Multiple collections were made within the Brule River drainage in Wisconsin: one of spring-run spawning adults, one of fall-run adults, and four from Brule River tributaries. Significant allele frequency differences were observed among the 15 collections for 13 out of 21 loci examined (P < 0.05). Statistically significant differences occurred among rainbow trout from different drainages and among the four site-specific samples from Brule River tributaries. No significant differences in allelic frequencies occurred between fall-run and spring-run adult fish. Genetic fixation values Ft indicated that about 2.6% of the total genetic variation occurred among the 10 drainages and that about 2.1% occurred among the six Brule River samples. Groups of collections identified by cluster analysis of genetic distances usually contained samples that were geographically proximate, except where the number of adult spawners was believed to be less than 50. The level of population differentiation reported here for Lake Superior was less than that previously reported for native rainbow trout populations from Pacific coastal drainages or that observed for introduced brown trout resident along the south shore of Lake Superior. The spatial units of focus for management of rainbow trout in Lake Superior should be groups of geographically proximate small streams, and possibly individual large drainage systems.

Persistence of the Native Rainbow Trout Type following Introduction of Hatchery Trout

The Santa Ana River, California, originally contained native coast rainbow trout, but repeated introductions of hatchery-reared rainbow trout and Lahontan cutthroat trout have subsequently been made. Twenty-four morphological characters of samples of native coast rainbow trout, hatchery-reared rainbow trout, and cutthroat trout, and recent Santa Ana River rainbow trout were compared using the D2 statistic to determine the extent that the native type was modified by introductions. The character mean of the recent Santa Ana sample was 10.8 D2 units away from that of the cutthroat trout sample, 7.3 units from the hatchery-reared rainbow trout sample mean, but only 3.0 units from the native rainbow trout sample mean. Pure Lahontan cutthroat trout have disappeared from the Santa Ana River and trout recently occupying this river closely resemble the native coast rainbow trout.