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Notes: The successful application of genetic stock identification (GSI) in mixed fisheries for Pacific salmon species has demonstrated clearly the potential of the approach as an aid to effective management of salmonid populations. Low levels of genetic variability detectable by protein electrophoresis have limited its utilization in Atlantic salmon Salmo salar management. However, recent developments in the detection of highly variable minisatellite loci, mean that the GSI technique is now applicable in this species. An extensive baseline survey of the River Shannon system in Ireland, involving a total of 1252 juvenile Atlantic salmon collected from nine tributaries, screened for three highly variable minisatellite DNA loci (Ssa-A45/1, Ssa-A45/2/1 and Str-A9), presented a suitable database to assess this type of mixed fisheries approach. Allozyme analysis, carried out on the same fish, allowed the performance of GSI on minisatellite DNA data to be compared directly with conventional data using simulations. Initial tests involved the creation of ‘mixture samples’ of specified compositions from the database, to determine the bias involved and the degree of precision achievable in the estimation of the composition of the mixture sample. Iterations of this procedure, simulated resampling of a mixture stock, thus enabled bias and precision to be estimated. The effect of size of the mixture sample was also assessed in this way. It was then possible to examine the compositions of actual mixture samples (using minisatellite DNA analysis only), which consisted of 200 unmarked grilse (one sea-winter) and 50 unmarked multi-sea-winter salmon, collected as they passed upstream through traps located near the base of the system. Sampling in this case involved the non-destructive collection of adipose fin cores (an important consideration as valuable broodstock were involved). The initial analysis revealed that allozymes require much larger sample sizes than minisatellites to achieve comparable accuracy and precision. It also appeared that GSI analysis, based on just three minisatellite loci, can provide very useful estimates of stock composition, even from a mixture sample comprising of stocks from within a single river system.

Notes: The extent of genetic variation in wild Atlantic salmon parr, Sulmo salur L., from river systems in Ireland, Iceland and eastern Canada, was investigated using starch gel electrophoresis. Within Ireland, seven polymorphic enzyme loci (sAAT-4*, GPI-1*, IDDH-1*, IDDH-2*, IDHP-3*, MDH-3* and mMEP-2*) were screened in nine different rivers and nine tributaries from the River Blackwater. Significant heterogeneity in gene frequencies occurred between riverine samples and between samples from tributaries of the River Blackwater. Variation between tributaries was as great as between rivers elsewhere in the country. Levels of population differentiation were comparable to those found in other regions throughout the range of the species, and temporal stability in gene frequencies was apparent when the results were compared with previously published data. Screening of riverine samples from Iceland and eastern Canada (Newfoundland and New Brunswick) allowed the Irish results to be considered in a broader context. Irish salmon cluster in the western European group, to which may be added Icelandic populations. Salmon from eastern Canada show a high level of genetic distinctiveness from the European group.

Notes: We used electrophoresis to determine the number and characteristics of genetically distinct stocks of odd-year pink salmon in Washington and southern British Columbia. We analysed 5128 fish from 52 collections (taken in 1985, 1987 and 1989). We observed genetic variation at 53 enzyme-coding loci, 19 of which were polymorphic at the Po-95 level in at least one stock. Genotypic proportions conformed to Hardy-Weinberg expectations in nearly all cases. The genetic profiles of individual populations were generally stable over the three cycle years studied. Significant differences in allele frequencies at sAAT-3*, PEP-LT* and PGDH* for several stocks were, however, noted between this study and previously reported data for pink salmon. We used G-tests and cluster analysis of genetic distances to evaluate genetic interrelationships among collections and to define genetically distinct stocks. Differentiation among stocks exhibited a clear geographic pattern with three major clusters of stocks recognizable: (1) Hood Canal and Washington Strait of Juan de Fuca stocks, (2) Puget Sound, Fraser River, and southern Canada South Coast stocks, and (3) northern Canada South Coast stocks and Canada North Coast stocks. Computer simulations using 14 and 28 loci, and sample sizes of 15C600, demonstrated that accurate estimates of stock-group composition could be obtained for pink salmon fisheries having a considerable range of stock compositions. The simulations revealed that approximately 50% fewer fish were required to obtain a given level of precision of stock group composition estimates with 28 loci as with the set of 14 loci used in previous investigations.

Notes: Data on geographical variation in allele frequencies at enzyme coding loci in Atlantic salmon from the British Isles were collated from published and unpublished sources. Statistically significant differences in allele frequencies were found among samples both within and among river systems, suggesting that the Atlantic salmon in the British Isles is not a panmictic population and that even within major river systems it cannot be treated as a single genetic stock for fisheries management purposes. Although there was some evidence of regional differences in the frequency of some rare alleles, most single-locus variation did not show strong geographic patterns, with the exception of the AAT-4* locus at which allele frequencies had a significant latitudinal cline. There was some evidence for the existence of genetically-distinct celtic and boreal races of Atlantic salmon in the British Isles as previously has been suggested. Multiple regression analyses revealed associations between genetic variation and local environmental conditions (i.e. between variation at MEP-2* and both temperature and local river gradient), providing additional evidence for adaptive population divergence in the species.

Notes: Genetic analysis of the four Trisopterus (Gadidae) taxa suggests that the interrelationships of the two morphs of poor cod (T. minutus minutus in the Atlantic and T. minutus capelanus in the Mediterranean) should be reconsidered. The Mediterranean poor cod T. m. capelanus is more closely related to bib T. luscus than to the Atlantic poor cod, so the population structure in the Atlantic and Mediterranean poor cod must be considered separately. Among 635 Atlantic individuals there was some evidence of poor cod population differentiation (allele frequency heterogeneity test P 〈0·0005; FST=0·0135, P≤0·0005). Levels of genetic variation were similar to those reported for related gadoid species. Some differentiation was present on the Norwegian coast (samples from Trondheimsfjord) and between the Faeroe Islands (Faeroe Bank) and the adjacent European coastal location. In contrast no statistically significant population differentiation was evident in Mediterranean poor cod, but fewer samples and individuals were screened.

Notes: The genetic composition of consecutive year classes of two farmed rainbow trout, Oncorhynchus mykiss (Walbaum), strains was assessed, using starch gel electrophoresis of 11 enzymes encoded by a minimum of 23 loci, many of which have been shown to be polymorphic in previous studies. Angle frequencies at the majority of polymorphic loci varied significantly between year classes of each strain. Several alleles which were present at low frequency in the 1900 year classes, were absent in the samples from the 1991 cohorts. However, mean heterozygosity per locus (H) did not differ significantly between year classes of either strain, illustrating that allelic diversity is a more sensitive indicator of loss of genetic variability than mean heterozygosity. This heterogeneity between cohorts is probably due either to broodstock maintenance practices such as the use of insufficient numbers of spawners, or, in the case of one strain, to bottlenecking caused by selection for late maturation and increased growth rate. Genetic monitoring of all year classes of reared strains is suggested, if insufficient breeding and distribution records are available from egg producers. Such records are often unavailable in commercial situations.

Notes: The effects of dietary α-tocopheryl acetate supplementation and different slaughtering methods were investigated on the flesh quality of farmed market-size turbot Scophthalmus maximus (L). Turbot were divided into three groups and fed commercial diets, supplemented with different levels of α-tocopheryl acetate at the following dietary inclusion levels: 72 (100), 547 (500), 969 (1000) (mg of α-tocopheryl acetate kg−1 diet, analytical values with diet codes in brackets). After 5 months, fish (mean weight 1056 ± 19.7 g) from each dietary treatment were sampled, applying three different slaughtering methods: (A) bleeding in ice water; (B) thermal shock, no bleeding; (C) percussion followed by bleeding in ice water. The time course of rigor mortis was evaluated, using pH, rigor index and mechanical compression tests. The results showed that the three parameters corresponded very well. Percussive stunning resulted in higher initial post-mortem pH (P 〈 0.01) and a significantly delayed onset of rigor mortis (P 〈 0.05). Diet significantly affected shelf-life, with fillets from fish fed diets 500 and 1000 having lower TBARS (thiobarbituric acid reactive substances) numbers from day 2 (P 〈 0.001) and less colour deterioration from day 7 of storage on ice onwards (P 〈 0.05). These results suggest that an increase in dietary α-tocopheryl acetate before slaughter as well as careful selection of the slaughtering method may greatly enhance the flesh quality of market-size turbot.

Notes: Juvenile turbot (45 g, SE = 1.3) were reared under three photoperiods, 08L:16D, 12L:12D and 20L:04D at slightly elevated ambient temperature for Ireland. Over the 297-day experimental period, the overall growth rate of the 12L:12D (0.82% d−1) treatment was higher than for both 08L:16D (0.80% d−1) and 20L:04D (0.77% d−1). Overall relative feed intake (FI = % consumption*day−1) was higher for the 20L:04D (FI = 0.81% d−1, SE = 0.06) treatment than for the 08L:16D (0.63% d−1, 0.04) and 12L:12D (0.64% d−1 0.04) treatments, whereas feed conversion efficiency (FCE = weight gain* consumption−1) was lower in the 20L:04D (FCE = 0.67, SE = 0.08) group when compared with the 08L:16D (0.88, 0.06) and 12L:12D (0.88, 0.06) treatments. Present results show that the long-term extended fixed photoperiod may act as an irritant, inducing stress, suppressing growth and reducing feed utilization. It is hypothesized that the progression of size-dependent hierarchies over time can be divided into two distinct phases herein referred to as ‘hierarchy resolution’ and ‘hierarchy stabilization’ phases (or phases 1 and 2) characterized by increasing and decreasing growth heterogeneity respectively. Growth heterogeneity is measured as coefficient of variation of weight and rank correlation of initial weight of a phase and corresponding growth rate.

Notes: Species or strains of fish may be translocated for farming, where the only access to the wild is via inadvertent escapes, or for stocking, where deliberate releases are undertaken. In either case, it is important that the translocated animals are representative of the donor population(s) in terms of genetic composition and level of variability. Many studies have shown that this ideal is difficult to achieve, the major reason being the use of inadequate numbers or composition of broodstock as founders of a strain. Also, where more than one conspecific population is involved, there may be outbreeding depression problems. In the case of farming, measures to improve the introduced strain genetically are likely to be undertaken, e.g. breeding programmes, manipulation of sex and ploidy, transgenic techniques. Such approaches are necessary economically, but can alter genetic make-up. Thus, stringent attempts must be made to minimize escapes or reduce their impact should they occur. With stocking, genetic change during captive rearing should be avoided. No strain manipulation should be undertaken, and other agents of change should be minimized. Stocking may result in hybridization with related species or with endemic populations of the same species. In either case, there can be detrimental genetic effects on the native forms. To be able to identify subsequently any genetic changes in reared strains, whether intended for farming or stocking, wild population composition should be determined, using appropriate molecular techniques. Such molecular methods will demonstrate the degree of interpopulation differentiation and, thus, reproductive isolation. The same markers should then be used in each subsequent generation (in the hatchery and after escape or reintroduction to the wild) to monitor any changes in genetic composition or variability. Markers should include microsatellite DNA loci, but the inclusion of more than one type of marker is recommended. However, as the aforementioned markers are not considered to be influenced by natural selection, they give no information on the adaptive nature of such differences. For this reason, it is suggested that markers influenced by selection should be investigated. Monitoring a strain subsequent to deliberate or inadvertent release can be undertaken using genetic markers, either deliberately enhanced by breeding or occurring naturally. Highly variable minisatellite DNA loci have been used as family markers in farmed escape studies with Atlantic salmon. These investigations have demonstrated significantly superior survival of native strains compared with farmed salmon in natural stream conditions. These latter results, demonstrating fitness differences, were strongly indicative of local adaptation. Thus, methods exist to monitor the genetic effects of translocation and stocking. However, a holistic approach should be taken to such exercises, where genetics forms part of a wider suite of considerations.

Notes: Fish fillet quality has been shown to be influenced by the level of antioxidants in preslaughter diet. Thus, an experiment was conducted to study the effect of different levels of vitamin E and C on the fillet quality of market-size reared turbot (Scophthalmus maximus). Turbot of a mean initial weight of 347 ± 20 g were divided into four groups and fed commercial turbot diets (60% protein, 12% fat), supplemented with α-tocopheryl acetate (mg kg−1) and ascorbyl-2 monophosphate (mg kg−1) at the following dietary levels: 500/100, 1000/100, 100/1000, 100/100 respectively. Over a dietary supplementation period of 15 weeks, fish were fed to satiation and reached a final mean weight of 916 ± 29 g. α-Tocopherol levels increased significantly (P 〈 0.001) in tissue (i.e. muscle, liver, heart and kidney) of fish fed diets containing elevated levels of α-tocopheryl acetate. In ice storage, fillets of these fish exhibited significantly lower (P 〈 0.001) levels of lipid oxidation, and showed significantly less (P 〈 0.001) colour deterioration (higher hue angle and lower chroma). Elevated dietary α-tocopheryl acetate levels had a negative effect (P ≤ 0.001) on the concentration of ascorbic acid in muscle tissue. An increase in dietary vitamin C did not have any detectable effect on fillet quality. Prolonged feeding times had a negative effect on lipid oxidation (P 〈 0.001) and colour deterioration (P 〈 0.01). These results suggest that increased dietary α-tocopheryl acetate could prevent colour deterioration and lipid oxidation of turbot fillets in retail storage on ice.