Tendency For Fish Research Articles

Natural selection on MHC IIβ in parapatric lake and stream stickleback: Balancing, divergent, both or neither?

Major histocompatibility complex (MHC) genes encode proteins that play a central role in vertebrates' adaptive immunity to parasites. MHC loci are among the most polymorphic in vertebrates' genomes, inspiring many studies to identify evolutionary processes driving MHC polymorphism within populations and divergence between populations. Leading hypotheses include balancing selection favouring rare alleles within populations, and spatially divergent selection. These hypotheses do not always produce diagnosably distinct predictions, causing many studies of MHC to yield inconsistent or ambiguous results. We suggest a novel strategy to distinguish balancing vs. divergent selection on MHC, taking advantage of natural admixture between parapatric populations. With divergent selection, individuals with immigrant alleles will be more infected and less fit because they are susceptible to novel parasites in their new habitat. With balancing selection, individuals with locally rare immigrant alleles will be more fit (less infected). We tested these contrasting predictions using three-spine stickleback from three replicate pairs of parapatric lake and stream habitats. We found numerous positive and negative associations between particular MHC IIβ alleles and particular parasite taxa. A few allele-parasite comparisons supported balancing selection, and others supported divergent selection between habitats. But, there was no overall tendency for fish with immigrant MHC alleles to be more or less heavily infected. Instead, locally rare MHC alleles (not necessarily immigrants) were associated with heavier infections. Our results illustrate the complex relationship between MHC IIβ allelic variation and spatially varying multispecies parasite communities: different hypotheses may be concurrently true for different allele-parasite combinations.

Heritability and genetic correlation of abdominal versus caudal vertebral number in the medaka (Actinopterygii: Adrianichthyidae): genetic constraints on evolution of axial patterning?

Variation in the number of abdominal vs. caudal vertebrae is an important source of morphological diversification of fish. It is not clear, however, whether abdominal and caudal regions evolve independently. Regressions of offspring on parents demonstrated substantial additive genetic variation within populations, i.e. heritability, in both abdominal and caudal vertebral numbers of the medaka (Oryzias latipes). However, the heritability of caudal vertebrae tended to be smaller than that of abdominal vertebrae in some estimations, suggesting that abdominal and caudal regions are controlled by separate developmental modules. Furthermore, genetic correlation between abdominal and caudal vertebral numbers, estimated using full-sib family means, was negative but weak, supporting independent evolution. In addition, substantial genetic differentiation among populations was demonstrated in abdominal vertebral numbers, but not in caudal numbers. These results support our view that Jordan's rule, a geographical tendency for fish from higher latitudes to have more vertebrae, in this fish reflects local adaptations of abdominal vertebral numbers. In contrast, the low heritability of caudal vertebrae may reflect the intrinsic invariability of genes associated with a change in caudal vertebral numbers. This genetic constraint may have restricted morphological diversification of not only the medaka, but also the Order Beloniformes as a whole. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 96, 867–874.

Regional variation in maturation of sandeels in the North Sea

Abstract Boulcott, P., Wright, P. J., Gibb, F. M., Jensen, H., and Gibb, I. M. 2007. Regional variation in maturation of sandeels in the North Sea. – ICES Journal of Marine Science, 64: 369–376. The current assessment of lesser sandeel (Ammodytes marinus) in the North Sea assumes a single stock and a knife-edge maturity ogive. However, there is evidence that the North Sea stock consists of several reproductively isolated components, raising the possibility of demographic differences among regional aggregations. We examine regional variation in size- and age-at-maturity in four components of the North Sea stock. Surveys in 1999 indicated pronounced regional differences in length- and weight-at-age, implying a disparity in growth rate across the North Sea. Logistic regression revealed that the onset of maturity was significantly related to regional distribution, in addition to length and age, with a tendency for fish off the UK's northeast coast to mature later and smaller than elsewhere. No significant effect of year on either growth or length-at-maturity was revealed from a comparison with other data collected in 2004. The results show that important regional phenotypic variation not currently represented in stock assessments could have implications for the local sustainability of sandeel aggregations.

Effect of variable food levels on reproductive performance of breeding female three‐spined sticklebacks

The study examined the response to variation in food ration within a breeding season on components of the reproductive performance of mature female three‐spined sticklebacks Gasterosteus aculeatus, a batch spawner. The main effect of food availability was on the duration of the inter‐spawning interval (ISI). Low ration resulted in an increase in the number of days until the next spawning. A low ration during one inter‐spawning interval increased the length of the next ISI, even if there was a high ration in the latter. Females that experienced high rations for two successive ISIs showed an increase in batch fecundity over the successive spawnings. There was no tendency for fish on low rations to produce bigger eggs or eggs with higher lipid concentration. Females on low ration had a lower carcass dry matter concentration and a lower liver dry weight immediately after their third spawning. Female sticklebacks responded to a low ration with little change in egg number or size, but a slight reduction in physiological condition. Egg characteristics and, to a lesser extent, batch fecundity are insensitive to current rate of food consumption, but the interval between spawnings is sensitive to both current and previous rates of consumption.

Evidence for density‐dependent growth in North Sea gadoids

The classical view on density‐dependent growth is that an increase in population density heightens intraspecific competition for food, leading to reduced food intake and depressed growth. This paper summarizes the analysis of English Groundfish Survey, International Young Fish Survey and ICES Roundfish Working Group data for evidence of density‐dependent growth of I‐ and II‐group cod, haddock and whiting in the North Sea.Within Roundfish areas there was a negative relationship between growth and density in some instances, but it was small. However, there were persistent differences in both growth rate and density between Roundfish areas. In all cases, except for I‐group cod, there appeared to be a tendency for fish in low‐density areas to be larger than fish in high‐density areas; this might be due to feeding competition but other explanations are possible. The results urge caution in interpreting commercial catch data for evidence of density‐dependent growth, since changes in fishing effort in particular areas could significantly bias the conclusions.There was evidence of enhanced survival of small fish in good year‐classes; this would depress the mean size at age, thereby mimicking the effects of density‐dependent growth.

Movements of Atlantic Halibut (Hippoglossus hippoglossus) in the Canadian North Atlantic

The results of Atlantic halibut (Hippoglossus hippoglossus) tagging experiments conducted in Northwest Atlantic Fisheries Organization (NAFO) Subareas 3 and 4 between 1958 and 1973 were reexamined. Data from the 230 recaptures indicated a tendency for fish released on the Scotian Shelf to move to the northeast, while fish released on the Newfoundland Grand Bank showed no preferred direction of movement. The Laurentian Channel does not appear to be a barrier to migration for this species. Small (<75 cm) fish moved further than larger fish. The seemingly limited movement by larger fish may be due to acyclic annual migration between feeding and spawning grounds, similar to that suggested for Pacific halibut (Hippoglossus stenolepis). The extensive movement of Atlantic halibut throughout most of the Canadian Northwest Atlantic suggests that a single area would be the most feasible management unit, encompassing the Scotian Shelf and southern Grand Bank regions.

A Study of Condition (Weight for Length) of Australian Barracouta, Thyrsites atun (Euphrasen)

Regression of weight in the round (w) on length to caudal fork (I) was calculated for 6571 barracouta from southern Victoria and 2711 from south-eastern Tasmania. The equations for the regressions, which differ significantly in position but not in slope, are respectively w = 0.0572 l2.360588 w = 0.1064 l2.239524 The values of the exponents are unusually low. A condition factor Kn was obtained for each fish by dividing the observed weight by the weight estimated from the regression, and geometric mean Kn was calculated for each month for each of the two regions. The mean for southern Victorian fish varied within the year in much the same way in each of three successive years, with three highs and three lows from early spring through early winter, but was consistently higher in 1950-51 than at the corresponding period of the year in 1949-50 or 1951-52. A similar pattern of within-year variation is suggested by the scantier data for other years, and likewise for south-eastern Tasmanian fish. All changes in mean Kn are closely paralleled by those in mean Kn,c the corresponding factor for beheaded eviscerated fish. It is also shown that changes in density of the fish are negligible. Thus the rises and falls in mean Kn represent true increments and decrements of growth in weight and volume of trunk muscle (edible flesh), unassociated with growth in length. There is a tendency for fish with filling gonads to have better condition than ripe, spent, recovering, or immature individuals, but it does not explain the major part of the variation in condition observed. Neither is there any apparent relationship between mean Kn and percentage of the monthly sample affected by the sporozoan Chloromyxum or the cestode Tetrarhynchus, which cause the conditions known as "milky" and "wormy" and are the only parasites of barracouta that occur in the trunk musculature. It seems most likely that the changes in mean Kn signify a complex interplay between assimilation on the one hand and the energy demands of migratory and food-seeking activity on the other. Oil content as a percentage of original (wet) weight was determined separately for fillet (edible flesh), viscera, and head of each of 66 south-eastern Tasmanian barracouta. There is a highly significant correlation between the oil content of each portion and the Kn of the fish. Regressions are given, and indicate that oil contents for fish of average condition (Kn = 1.000) are 4.39, 8-08, and 7.98 per cent. for fillet, viscera, and head respectively.

Tunny Investigations made in the North Sea on Col. E. T. Peel's Yacht, “St. George,” Summer, 1933. Part I. Biometric Data

1. Details are given of the types of hooks lost in tunny in the North Sea in the summer of 1933.2. Data are given on the measurements made on thirty-two large migrating fish caught in the North Sea in August and September, 1933.3. In certain body proportions the tunny measured differ from those in the G4 Group (200 to 260 cm. in length) given by Heldt for fish from Tunis and by Frade for fish from Algarve on the south coast of Portugal, while in some characters they resemble the Tunis fish and in others the Algarve fish, but all the North Sea fish were between 232 and 271 cm. in length.4. It was found that there was a tendency for fish with short second dorsal fins to have short first dorsal, anal, and caudal fins, and for those with long second dorsals to have these other three fins long.5. Measurements were made to supply data on the condition of the fish.