Genotypes at 91 microsatellite loci in three full-sib families were used to search for QTL affecting body weight (BW) and condition factor in North American Atlantic salmon (Salmo salar). More than one informative marker was identified on 16-18 linkage groups in each family, allowing at least one chromosomal interval to be analyzed per linkage group. Two significant QTL for BW on linkage groups AS-8 and AS-11, and four significant QTL for condition factor on linkage groups AS-2, AS-5, AS-11, and AS-14 were identified. QTL for both BW and condition factor were located on linkage groups AS-1, 6, 8, 11, and 14 when considering both significant and suggestive QTL effects. The largest QTL effects for BW (AS-8) and for condition factor (AS-14) accounted for 20.1 and 24.9% of the trait variation, respectively. Three of the QTL for BW occur on linkage groups where similar effects have been detected on the homologous regions in either rainbow trout (Oncorhynchus mykiss) or Arctic charr (Salvelinus alpinus). Heredity (2005) 94, 166-172.

SUMMARYIn fishes, performance failure at high temperature is thought to be due to a limitation on oxygen delivery (the theory of oxygen and capacity limited thermal tolerance, OCLTT), which suggests that thermal tolerance and hypoxia tolerance might be functionally associated. Here we examined variation in temperature and hypoxia tolerance among 41 families of Atlantic salmon (Salmo salar), which allowed us to evaluate the association between these two traits. Both temperature and hypoxia tolerance varied significantly among families and there was a significant positive correlation between critical maximum temperature (CT max ) and hypoxia tolerance, supporting the OCLTT concept. At the organ and cellular levels, we also discovered support for the OCLTT concept as relative ventricle mass (RVM) and cardiac myoglobin (Mb) levels both correlated positively with CT max (R 2 =0.21, P<0.001 and R 2 =0.17, P=0.003, respectively). A large RVM has previously been shown to be associated with high cardiac output, which might facilitate tissue oxygen supply during elevated oxygen demand at high temperatures, while Mb facilitates the oxygen transfer from the blood to tissues, especially during hypoxia. The data presented here demonstrate for the first time that RVM and Mb are correlated with increased upper temperature tolerance in fish. High phenotypic variation between families and greater similarity among full-and half-siblings suggests that there is substantial standing genetic variation in thermal and hypoxia tolerance, which could respond to selection either in aquaculture or in response to anthropogenic stressors such as global climate change.

European Atlantic salmon (Salmo salar) differ in skin pigmentation and shape from the North American lineage of Atlantic salmon but the genetic basis of these differences are poorly understood. We created four large (N ¼ 300) backcross families by crossing F1 hybrid male siblings to two females from the European and two from the North American aquacultural strains. We recorded 15 morphological landmarks and two skin pigmentation, three growth and three condition traits on parr. The backcross families were genotyped for at least 129 SNPs (single nucleotide polymorphisms) within expressed sequence tags (ESTs) spaced throughout the Atlantic salmon linkage map. The high polymorphism and low rates of crossover in our hybrid sires provided enough statistical power to detect 79 significant associations between SNP markers and quantitative traits after experiment-wide permutation analysis for all families within traits. Linkage group AS22 contained a quantitative trait loci (QTL) for parr mark number; its homolog AS24 contained a large QTL, which explained 26% of the phenotypic variance in parr mark contrast. We found 25 highly significant QTLs for body shape and fin position on seven different linkage groups, and 16 for growth and condition on six different linkage groups. QTL(s) for pectoral fin position, caudal peduncle position, late parr growth and condition index were associated with an SNP on linkage group AS1, which was linked to the sex-determining locus. Our work adds to the evidence that much of the variation in growth rate, shape and skin pigmentation observed among Atlantic salmon parr from different natal streams is genetic.

We studied the relationships between tissue dynamics and bioenergetics of the anadromous American shad (Alosa sapidissima) homing to the St. Johns (Fla.), York (Va.), and Connecticut (Conn.) Rivers and the life history characteristics of these populations. Shad in the three populations studied differed in the degree of development of the gonads at river entry, in the absolute and relative energy allocation to reproductive products vs. migration, and in the extent of total energy depletion during the migration. St. Johns River fish consumed 70–80% of their total energy reserves to reach the spawning grounds and spawn. In this population all shad die following spawning. York River shad consumed ~30% and Connecticut River shad 40–60% of their energy reserves to migrate to the spawning grounds, spawn, and return to the sea. In these populations 25 and 35%, respectively, of the spawning adults survive to spawn again. The principal determinants of energy use were migration distance and river gradient. We rejected the hypothesis that the latitudinal cline in adult survival results from differences in energy use during migration. We concluded that interpopulation differences in energy allocation to migration vs. reproduction are a consequence, rather than a cause, of the different life history strategies exhibited by populations of shad over its Atlantic Coast range. A similar pattern is apparent in other anadromous species: obligate semelparous species use > 70% of their energy reserves to reach the spawning areas and spawn; iteroparous species allocate more energy to postreproductive reserves at the expense of reproductive products thereby ensuring a successful return migration to the sea. Freshwater swimming speeds also appear to differ in a consistent way between semelparous and iteroparous species. Semelparous species swim at close to maximum sustained speed thereby minimizing the duration of the migration. Iteroparous species swim at speeds yielding near optimum energy efficiency (J∙kg−1∙km−1) thereby minimizing the energy cost of migraiton.Key words: American shad, (Alosa sapidissima); migration, bioenergetics, life history tactics, latitudinal clines, swimming speeds, energy allocation, anadromy

No abstract