BackgroundQuantitative trait locus (QTL) studies show that variation in salinity tolerance in Arctic charr and rainbow trout has a genetic basis, even though both these species have low to moderate salinity tolerance capacities. QTL were observed to localize to homologous linkage group segments within putative chromosomal regions possessing multiple candidate genes. We compared salinity tolerance QTL in rainbow trout and Arctic charr to those detected in a higher salinity tolerant species, Atlantic salmon. The highly derived karyotype of Atlantic salmon allows for the assessment of whether disparity in salinity tolerance in salmonids is associated with differences in genetic architecture. To facilitate these comparisons, we examined the genomic synteny patterns of key candidate genes in the other model teleost fishes that have experienced three whole-genome duplication (3R) events which preceded a fourth (4R) whole genome duplication event common to all salmonid species.ResultsNine linkage groups contained chromosome-wide significant QTL (AS-2, -4p, -4q, -5, -9, -12p, -12q, -14q -17q, -22, and −23), while a single genome-wide significant QTL was located on AS-4q. Salmonid genomes shared the greatest marker homology with the genome of three-spined stickleback. All linkage group arms in Atlantic salmon were syntenic with at least one stickleback chromosome, while 18 arms had multiple affinities. Arm fusions in Atlantic salmon were often between multiple regions bearing salinity tolerance QTL. Nine linkage groups in Arctic charr and six linkage group arms in rainbow trout currently have no synteny alignments with stickleback chromosomes, while eight rainbow trout linkage group arms were syntenic with multiple stickleback chromosomes. Rearrangements in the stickleback lineage involving fusions of ancestral arm segments could account for the 21 chromosome pairs observed in the stickleback karyotype.ConclusionsSalinity tolerance in salmonids from three genera is to some extent controlled by the same loci. Synteny between QTL in salmonids and candidate genes in stickleback suggests genetic variation at candidate gene loci could affect salinity tolerance in all three salmonids investigated. Candidate genes often occur in pairs on chromosomes, and synteny patterns indicate these pairs are generally conserved in 2R, 3R, and 4R genomes. Synteny maps also suggest that the Atlantic salmon genome contains three larger syntenic combinations of candidate genes that are not evident in any of the other 2R, 3R, or 4R genomes examined. These larger synteny tracts appear to have resulted from ancestral arm fusions that occurred in the Atlantic salmon ancestor. We hypothesize that the superior hypo-osmoregulatory efficiency that is characteristic of Atlantic salmon may be related to these clusters.

Young‐of‐the‐year (age‐0) striped bass Morone saxatilis have been observed during late summer and fall in southern Gulf of St. Lawrence estuaries that may not support striped bass spawning. In this study, we tested the hypothesis that age‐0 striped bass in the Richibucto and Kouchibouguac rivers disperse there from the Miramichi River, which is located approximately 35 km north of the Kouchibouguac River and 55 km north of the Richibucto River. Beach seining of the coastline between these three rivers during summer in 1997 and 1998 confirmed the presence of age‐0 striped bass in the latter half of August but not before. Age‐0 fish distributions over time were consistent with movement from the Miramichi River to the Kouchibouguac and Richibucto estuaries. Microsatellite nuclear DNA and mitochondrial DNA analyses were performed to determine the genetic relatedness among striped bass from these estuaries. Age‐0 striped bass from the Shubenacadie River population in the Bay of Fundy, which is known to be genetically distinct from Gulf of St. Lawrence populations, and the Hudson River, New York, were used as out‐groups in the analyses. In all comparisons, significant haplotype and allelic differences were found between Gulf of St. Lawrence samples and the Shubenacadie River and Hudson River populations. However, significant haplotype or allelic differentiation was rarely observed in comparisons among samples from rivers within the Gulf of St. Lawrence. These results suggest that some of the age‐0 striped bass spawned in the Miramichi River leave their natal estuary in late summer and disperse through shallow coastal waters to other estuaries in the southern Gulf of St. Lawrence.

The retinoid concentration (determined colorimetrically) did not change significantly in retinyl acetate-supplemented (6 micrograms/ml) Eagle's Minimal Essential Medium containing 10% fetal calf serum when stored at -20 or 4 degrees C over 7 days. After the medium was incubated at 37 degrees C for 48 h, 37-49% of the retinoid remained, whether or not tissue (neonatal Syrian hamster cheek pouch) was present, and irrespective of explant age. The normal retinoid level in the tissue was approximately 0.25 micrograms per gram. Therefore, neonatal hamster cheek pouches, incubated in medium with the addition of 6 micrograms of retinyl acetate per ml of medium and undergoing mucous metaplasia and some mucous gland morphogenesis, were continually being exposed to retinoid levels which, though gradually decreasing, remained well above their normal physiological level.

Vitamin A levels in tissues of 20 normal adult hamsters on a standard diet were measured colorimetrically. No significant difference between male and female animals was found for any of the tissues sampled. The mean vitamin A value for blood plasma in 20 animals was 53.4 micrograms/dl. Mean values for liver, kidneys, flank skin and cheek pouch were 813, 1.29, 1.84 and 1.31 mg/g wet weight, respectively. The vitamin assay was less suitable for small organs such as trachea.