These aquaculture-oriented commentaries are not abstracts written by the original authors.  They reflect the opinions of someone else -- usually Roger Doyle.  Direct quotations from the papers or abstracts are marked with inverted commas.

45. Newly immigrated pathogens cause more trouble than they did back home
Increased virulence in an introduced pathogen: Haplosporidium nelsoni (MSX) in the Eastern Oyster Crassostrea virginica. 2000. Burreson, E.M., N.A. Stokes, and C.S. Friedman. Journal of Aquatic Animal Health 12:1-8.
          The authors used species-specific probes and DNA sequencing to confirm that a haplosporidian parasite in the Pacific oyster Crassostrea gigas in California is identical to a pathogen which has caused extensive moralities to another species of oyster (C. virginica) on the east coast of North America. It is also identical to, and probably originated from, a parasite found in Japanese C. gigas. C. gigas is known to have been transported to and cultivated on the east coast. The authors conclude that their results "document greatly increased virulence in a naive host–parasite association and reinforce potential dangers of intentional, but improper, introductions of exotic marine organisms for aquaculture or resource restoration".

44. Don't bother to hijack a hybrid.
Heterosis and outbreeding depression in interpopulation crosses spanning a wide range of divergence. 1999. Edmands, S. Evolution 53:1757-1768.
          "The intertidal copepod Tigriopus californicus was used as a model organism to look at effects of crossing distance on fitness and to investigate the genetic mechanisms responsible. Crosses were conducted between 12 pairs of populations spanning a broad range of both geographic distance (5 m to 2007 km) and genetic distance (0.2% to 22.3% sequence divergence for a 606-bp segment of the mitochondrial COI gene."
           The author found that the first generation hybrids showed some heterosis which was not related to the geographic or genetic distance separating the parents. However, mean fitness decreased and its variance increased in subsequent generations when the F1 hybrids mated among themselves. This hybrid breakdown problem in the later generations increased with the distance between the original parents. "Genetic interpretation of these patterns suggests that both the beneficial effects of dominance and the detrimental effects of breaking up coadaptation are magnified by increasing evolutionary distance between populations."
          Although there is nothing theoretically surprising about these results it is always nice to see theory proving out. The implications for fisheries conservation and aquaculture (by analogy) are: expect problems in the second generation or later when you start breeding hybrids. Expect bigger problems if the difference between the founding strains is bigger. If you hijack a hybrid from a fingerling supplier and multiply it, expect trouble. sedmands@usc.edu

43. Transgenic growth hormone genes not the only way to make an animal grow faster
Role of growth hormone in the genetic change of mice divergently selected for body weight and fatness. 1999. Bunger, L., and W.G. Hill. Genetical Research 74:351-360.
          This experiment was designed to discover the importance of growth hormone (GH) to the evolution of fast-growing mice. The authors selected lines of mice for high and low body weight for more than 50 generations, after which the high and low lines had diverged approximately 3-fold in their weight at 98 days. The authors then eliminated growth hormone from the metabolism of the mice by genetic "knock out", which they achieved by backcrossing a defective GH releasing factor receptor gene into both lines. Control high and low lines with the normal GH gene were also maintained.
          Both lines of mice carrying the knock-out gene, which were thereby deficient in GH, were much smaller than the normal control mice at 98 days. There is no doubt that growth hormone makes mice grow quickly. What is surprising is that the divergence of the high and low lines was almost as great in the absence of growth hormone (2.4-fold divergence) as in its presence (3.1-fold). The authors conclude that after appropriate scale transformation, "changes in the GH system contribute only a small part of the selection response in growth .... [and] other systems contributed most of the selection response". Fat percentage was also lower in all the GH-deficient lines.
          This experiment should interest the aquaculture community even though it was performed on mice. We know that transgenic fish carrying extra growth hormone genes, or modified genes that express GH continuously, are fast-growing fish -- sometimes very fast-growing. This ingenious knock-out experiment on mice is a hint that the converse may not be true. Selection of fast-growing fish by classical methods may evoke an entirely different kind of genetic change which does not involve growth hormone. Furthermore, it suggests that if crosses between high- and low-selected lines are used in searches for growth QTLs, the growth hormone system will not necessarily provide the best candidate genes. lutz.bunger@ed.ac.uk

42.  Marine breeding populations are bigger than fresh water populations
Microsatellite variation in marine, freshwater and anadromous fishes compared with other animals. 2000. DeWoody, J.A., and J.C. Avise. Journal of Fish Biology 56:461-473.
          The authors reviewed published and unpublished microsatellite data from many thousands of individuals from almost 80 species. "Freshwater fish displayed levels of population genetic variation roughly similar to those of non-piscine animals. In contrast, local population samples of marine fish displayed on average significantly higher heterozygosities and nearly three times the number of alleles per locus. Anadromous fish were intermediate to marine and freshwater fish." [numerical summary data omitted from the quotation].
          The paper notes that these results are consistent with earlier results using allozymes, and suggests that the consistent difference between fresh water and marine within-population genetic diversity is due to characteristic differences in evolutionarily effective population size. email:dewoody@arches.uga.edu

41. Frankenfish, information & money
Differentiating genomics companies. 2000. James, R. Nature Biotechnology 18:153-155.
          The author writes about companies that are applying genetics to human health, but his analysis applies equally well to genetics in aquaculture.
          In this paper by R. James three types of genomics companies are distinguished: product providers, information providers and technology providers. Companies in these three areas are now racing for primacy and moving into each other's commercial strategy space. The business development strategies of many of the best known companies are evaluated here, including the Perkin-Elmer subsidiary Celera Genomics which is much in the news for claiming patent protection for its human genome data. The question which interests Mr. James is how to invest money. The question which interests us is how to bet the future of the fish farm.
           If we apply Mr. James's analysis to aquaculture genetics we conclude that companies which provide proprietary products like vaccines or genetically improved broodstock and fingerlings can potentially make the highest profit but also experience the highest risk, in particular the risk that someone else will develop a product which is cheaper or more effective.
          Purveyors of aquaculture genetic information about genomic sequences, markers and maps are mostly but not entirely in the public sector. The opportunity to generate value from proprietary information about QTLs, pathogens and broodstock genotype-environment interaction in aquaculture is not being ignored, however. The commercial risk to information-suppliers is that their proprietary information will become "commodified" and freely available. Some people are even making a moral crusade out of the public right to raw genetic data. Spider Robinson neatly summed it up in the Toronto Globe & Mail on 18 March: "It's as though an explorer took the first photo of a zebra -- then claimed ownership of zebras, the concept of stripedness, and anything else substantially zebraic in nature".
          Both in human genomics and in aquaculture genetics there are companies that develop technology for use by other companies e.g. for on-farm broodstock improvement. This consulting company, Genetic Computation Ltd., falls into this category. James notes that such companies " though in some ways offering the lowest risk for investors, are always in danger of becoming generic or outdated as new ways for tackling a problem are developed."

40. Genetic rehabilitation of a tiny fish population
Establishing a captive broodstock for the endangered Bonytail chub (Gila elegans). 2000. Hedrick, P.W., T.E. Dowling, W.L. Minckley, C.A. Tibbets, B.D. Demarais, and P.C. Marsh. The Journal of Heredity 91:35-39.
          This is a fine example of a genetic management plan for an endangered fish. "Bonytail chub (Gila elegans) is one of the most imperiled freshwater fish species, persisting as a declining population of large and old individuals primarily in Lake Mohave on the lower Colorado River." A captive broodstock population was established in 1981 using very few fish. The authors make various calculations on the effective number of founders and the probable loss of diversity since 1981, and conclude that "including wild fish in the broodstock is essential to increase the amount of genetic variation. The approach given here could be applied to retain genetic variation in other endangered species in a captive broodstock until they have stable natural populations of adequate size."   philip.hedrick@asu.edu

39. Special strains for special places
Genotype x environment interaction of crossover type: detecting its presence and estimating the crossover point. 1999. Singh, M., S. Ceccarelli, and S. Grando. Theoretical and Applied Genetics 99:988-995.
          This paper presents a useful statistical framework for experiments to detect genotype-environment (GE) interaction, a term which refers to variability in the relative performance of strains in different environments. Information on this topic in aquaculture is often inconclusive or contradicts other information which, so far as we know or are willing to say, is equally believable.
          It should be noted that the root of the difficulty for the aquaculture community is, in fact, statistical. It takes a big experiment to reject the null hypothesis that the true value of the GE interaction is zero. It also takes a big experiment to reject the hypothesis that GE interaction is actually some number much greater than zero. In aquaculture, the mistake of believing that GE interaction is zero when it is really much larger can be costly -- like choosing the wrong strain or genetic improvement strategy for your grow-out system. Unfortunately, the statistical power of experiments to distinguish two alternative hypotheses is rarely reported. It is sad but true that experiments are usually designed to minimise the type of mistake which, in aquaculture, is the least costly.    m.singh@cgiar.org

38. Salmon kin don't stay together
An analysis of the distribution of juvenile Atlantic salmon (Salmo salar) in nature as a function of relatedness using microsatellites. 1999. Fontaine, P.M., and J.J. Dodson. Molecular Ecology 8:189-198.
          "Microsatellites were used to establish the relatedness of salmon fry (in their first summer of life) and parr (in their second and third summer of life) captured in adjacent territories. " The authors did not find that fish collected near each other were full sibs. This observation was contrary to their starting hypothesis, derived from theories of inclusive fitness and salmon rearing experiments at high densities, that close kin should associate with each other. The significance for genetic conservation would lie in the choice of sampling strategies for selecting broodstock, and also for choosing models for defining the evolutionarily significant units.

37. Tilapia kin do stay together
Kin cohesiveness and possible inbreeding in the mouthbrooding tilapia Sarotherodon melanotheron (Pisces Cichlidae). 1999. Pouyaud, L, E. Desmarais, A. Chenuil, J.F. Agnese, and F. Bonhomme. Molecular Ecology 8:803-812.
          The authors analysed gene frequencies at 4 microsatellite loci in tilapia shoals (natural aggregations) from rivers and from open water. They interpret their data on heterozygosity deficiencies and similarity indices to mean that in the open-water environments, "related individuals tend to aggregate, and that mating occurs preferentially within small groups of kin". This was not true of tilapia taken in the rivers. This finding, if it can be substantiated and if it also occurs in mouthbrooders like Oreochromis niloticus and mossambicus, would profoundly affect the estimation of inbreeding rates in extensive aquaculture systems.

36. Genetic signatures might identify the origin of fish pathogens
Two isolates of sea bass, Dicentrarchus labrax L., nervous necrosis virus with distinct genomes. 1999. Thiéry, R., C. Arnauld, and C. Delsert. Journal of Fish Diseases 22:201-207.
          The capsid protein gene of viral isolates from two sea bass populations (Atlantic and French Mediterranean) was cloned and sequenced. The two isolates of the nervous necrosis (SBNNV) nonadavirus showed numerous sequence differences in the region used for RT-PCR (reverse-transcriptase polymerase chain reaction) assay and diagnosis. This is further evidence (see #35 & #31) that a biogeographic database of aquaculture pathogens could be developed to trace the origins and causes of outbreaks. In some ways this might be more interesting, or at least more immediately useful, than biogeographic analysis of the aquacultural species themselves. Richard.Thiery@brest.cneva.fr

35. Genetic signatures might identify the origin of shrimp pathogens
Differentiation of BP-type baculovirus strains using in situ hybridization. 1998. Durand, S., D.V. Lightner, and J.R. Bonami. Diseases of Aquatic Organisms 32:237-239.
           The authors used several different molecular probes to test shrimp infected with BP-type viruses collected from several geographical areas. Their probes detected only the Pacific strain of BP, not the Atlantic strain, even though one individual shrimp appeared to have a double infection (both strains) . "These results suggest the existence of at least 2 different BP-type viruses and show that specific probes can be used to differentiate between them". (See #36 & #31).

34. Variation in inbreeding depression within a population
Inbreeding effects on resistance and transmission-related traits in the Silene-Microbotryum pathosystem. 1999. Ouborg, N.J., A. Biere, and C.L. Mudde. Ecology 81:520-531.
          Samples from 8 populations of S. alba (white campion, a flowering plant ) were subjected to 5 generations of sib mating to produce 65 inbred lines having theoretical inbreeding coefficients of 0, 0.25, 0.375, 0.5, and 0.59 per line. These lines were tested for two components of susceptibility to fungal infection -- direct resistance at the biochemical level and also indirect resistance conferred by having flowers that are relatively unattractive to the insect vector.
          The authors found that "the percentage of infected individuals differed significantly among populations, lines, and inbreeding levels, and both population-by-inbreeding level and line-by-inbreeding level interactions were significant. The most striking result was the strong variance in inbreeding effects among lines; inbreeding resulted in increased resistance in some lines and decreased resistance in others. " This research has its roots in the ecological genetic research programme of Janis Antonovics at the University of Virginia, winner of this year's Sewall Wright award.
          The importance of this study as a model of biological conservation and aquaculture is the unpredictability of the effect of inbreeding at the local population level. In some lines inbreeding even increased resistance. This is because the formal, calculated inbreeding coefficient of a population is actually the expectation (mean) of a stochastic process that involves sampling at the level of the pedigree (parental genealogy), the zygote, and the chromosome segment. (See #13).  In conservation and aquaculture, where every fish has value, some lineages and some animals within lineages are going to be much worse off than the calculated inbreeding coefficient of the population would indicate. The differential mortality which results from these sampling processes is evident in inbreeding studies on natural populations (such as #9 & #32 ). The resulting inbreeding genetic load (moralities) is not, however, taken into account in broodstock management plans.
          It was also interesting that in the plant-pathogen system the two modes of inbreeding resistance were genetically uncorrelated. In fish and shrimp, one would also expect to find many behavioral and biochemical modes of resistance to pathogens. Only some of these modes of resistance -- never the behavioral ones -- would be simulated by challenge tests.

33.  Local adaptation of fish
Effect of temperature and salinity on growth performance in anadromous (Chesapeake Bay) and nonanadromous (Santee-Cooper) strains of striped bass Morone saxatilis. 2000. Secor, D.H., T.E. Gunderson, and K. Karlsson. Copeia 100:291-296.
          Juvenile growth rates of the two strains of bass differed in their response to temperature and salinity. This is more evidence for the importance of genotype-environment interaction in the choice of broodstock of at least some aquacultural species, and the likelihood that GE interactions would soon develop, if they were not initially present in the broodstock, during selection in different types of aquaculture system (see #28 & #22).