If recovery programmes are to be initiated in England and Wales, it is very important to obtain information on how genetic variation is partitioned between the remaining populations for the endangered species Austropotamobius pallipes pallipes. A survey of the mtDNA genome, using 12 restriction enzymes revealed 3 haplotypes in 4 British populations. The study reveals a low level of genetic variation amongst four geographically distant populations. Moreover, the most widespread haplotype found in the British populations is also similar to those found in French populations; one of the rare haplotypes found in one English population is also widespread in French populations. Management of crayfish stocks may be possible at a national level however, a more extended study of mtDNA variation is needed to prove this conclusively.

The relationship between serum protein, immunoglobulin concentrations and protein molecular weight profile (PMWP) alterations of sea bass (131.3 ± 4.3 g) reared in sea water with sublethal concentrations of ammonia was studied over two periods totalling 116 days. During the exposure period (62 days) the first group (group 1) lived in sea water with 0.204 mg·L−1 unionized ammonia nitrogen equivalent to 12 % of the lethal concentration for 50 % of a population exposed for 96 h to ammonia (96-h LC50), whilst the second group (group 2) lived in sea water with 0.340 mg·L−1 UIA-N equivalent to 20 % of the 96-h LC50 of ammonia. Then, the two groups were left for a recovery period (54 days) in the same water as the control group (group 0). The determination of the total immunoglobulin (Ig) concentration was carried out by enzyme-linked immunosorbant assay (ELISA). Gel filtration columns were used for the serum PMWP. Serum Ig concentration of the exposed fish (group 2: 1.76 ± 0.43 mg·mL−1; group 1: 1.19 ± 0.33 mg·mL−1) was lower than the control group 13.39 ± 1.01 mg·mL−1) after 21 days of exposure period but this difference was reduced at the end of this period (day 62) and treated group Ig concentrations switched to higher than the control group after the recovery period (day 116, group 2: 9.75 ± 1.84 mg·mL−1; group 1: 7.50 ± 1.22 mg·mL−1 group 0: 6.38 ± 1.13 mg·mL−1). In fact, at the end of the experiment, the cumulative Ig production difference between fish exposed to ammonia and the control was less than 10%. Although a similar evolution of the Ig serum occurred with protein concentration, the serum protein concentration deficit of group 1 was restored at the end of the exposure period (group 2: 46.49 ± 2.34 mg·mL-1; group 0: 46.74 ± 1.97 mg·mL−1) and the cumulative production during the experiment was not significantly different between group 1 and group 0. However, this remained lower for group 2. During the exposure period, the PMWP of treated fish moved towards smaller molecular weight proteins. This alteration of the PMWP showed that the 0.2-kDa fraction increased, and another fraction appeared at the end of the exposure period. However, at the end of the recovery period, no difference was found between the PMWPs of control and treated fish. The alterations of the serum protein and Ig of fish reared, for a limited period (2 months), in water with sublethal concentrations of ammonia (20 % 96-h LC50 or less) should disappear completely after a few months in normal rearing conditions.

Management techniques in two sea scallop Placopecten magellanicus fisheries in Nova Scotia are compared and contrasted. In one, traditional management methods are used to protect the stock from overexploitation. In the other fishery, enterprise allocations in the form of quota shares are used to mimic property rights. Over the past decade, the fleets' reactions to stock conditions have been dramatically different. It is argued that the evidence supports a quasi-property management regime, though other factors are at play as well.

17α-ethynylestradiol sex-reversed males of Oreochromis aureus (pseudofemales, ΔF, genotype ZZ) are used in aquaculture to produce a male monosex population by crossing with ZZ homogametic normal males. When placed with males (M) and females (F) in the same spawning tank, the spawning rate of F is higher than for ΔF. In order to understand this phenomenon, comparisons were made between the behaviour of 18 F (446 ± 96 mm) and 18 ΔF (401 ± 59 mm). ΔF showed a more aggressive behaviour and were significantly more dominant than normal F in fighting pair experiments (F × ΔF) or in fighting group experiments in four different stocking densities (8, 12, 16 and 83 fish 10–3 l with F/ΔF RATIO = 1). ΔF were also more aggressive towards males than F were. The results support the idea that behavioural differences exist between F and ΔF. These differences are probably due to the effect of the sexual genotype on behaviour.

For centuries, several species of prawns and crabs have been raised from wild-caught juveniles in coastal brackish-water fish ponds in various countries of south east Asia. The Indonesian "tambaks" are well known examples of such traditional practices. In western countries, since the turn of the century, advances of marine biology and fast increase of marine fisheries enabled the development of large-scale production and release of larval stages of American and European lobsters in a fruitless attempt to restock natural populations. After the Second World War, the increasing demand for crustaceans in United States and Japan was satisfied by opening new prawn fisheries all over the world. A major breakthrough was achieved with the development of hatchery technologies for the penaeid prawn Penaeus japonicus (Hudinaga, 1942 in Japan) and the caridean prawn Macrobrachium rosenbergii (Ling, 1969 in Malaysia), which occurred during the first decades of the second half of this century. Together with the increasing market demand in developed countries for sea food, this led to a considerable interest of both public agencies and private investors in marine shrimp and prawn culture. In western countries, a large number of pioneering commercial ventures, often based on assumptions not scientifically founded, failed. Nevertheless, the aquaculture production of prawns mainly based on wild-caught juveniles increased in South-East Asia and Central America during the 1980s. This overall positive trend should not hide important failures which occurred at a local scale, such as the Taiwanese crisis of 1988 due principally to environmental degradation, resulting in severe disease problems and a near collapse of the farming activity. Following the early period of hatchery technology development, the major scientific achievements were related to food requirements and formulation of compound diets for larvae, juveniles and adults and to a better knowledge of diseases caused by bacteria and several viruses which have been identified from hatcheries and intensive farming ponds. Additional new technological advances have emerged from recent research in the fields of physiology (endocrinology) and genetics. By far, the major part of the world production of marine crustaceans relies on penaeid prawns and, to a lesser extent, on Macrobrachium species. However, some other species of marine crustaceans have potential for aquaculture.

The economic aspects of marine crustacean aquaculture should be considered together with those of the fishing industry: market prices are rather similar, depending on the quality of the product. The balance between market demand and production is an important constraint which, in turn, establishes the success of prawn farming. Since the early 1980s, crustacean aquaculture has increased tremendously in both Asiaand America: the world production for 1991 approximated 700,000 tons, with more than 600,000 tonsfrom penaeid prawn culture.

A simple system was used to simulate the effect of alternating toxic (paralytic shellfish poisoning toxins) and non-toxic microalgal diets on oyster feeding behaviors and rates of toxin accumulation. These experimental conditions were meant to reflect, to some extent, the incoming and outgoing fluxes of toxic algae observed at the mouth of the Penzé estuary (Northern Brittany, France). Physiological and toxicological parameters were estimated based on fluorescence measurements recorded continuously at the outlet of each experimental tank, which contained a single oyster. Q tox, this variable describes toxin uptake in oysters, it was used (instead of the toxin ingestion rate): i) in simple graphical analyses, ii) as well as in one- and two-compartment models. Results show that toxin uptake varies widely from one individual to another and is not proportional to the concentration of toxic algae in sea water. A one-compartment model with individual fluorescence recordings as “input” data gave questionable results, however, a two-compartment model was found to effectively describe contamination kinetics in oysters. Limitations of this model as well as possible improvements are discussed.

The Pacific oyster (Crassostrea gigas) is an important commercial species in the US Pacific Northwest with a history of production initially based on wild-caught seed imported directly from the Miyagi region of northern Japan (1920s–1970s) followed by an extended period of seed collection from a small number of naturalized, self-recruiting populations in US estuaries (early 1970s-present) and more recently through large-scale hatchery production of seed oysters (mid 1970s-present). I studied the genetic level consequences of each of these major transformations of the oyster industry by examining the patterns of private alleles (bands unique to one sample), the number of polymorphic loci, expected heterozygosity, genetic distance between populations and genetic divergence between individuals within and among three native Pacific oyster populations in Japan (Hiroshima, Miyagi, Midori River), five naturalized populations in North America (Pipestem Inlet BC, Nootka Inlet BC, Dabob Bay WA, Willapa Bay, WA, and Tillamook Bay, OR), two in New Zealand (Chance Bay and Kaipara Harbor), and seven domesticated and selectively bred cohorts from an ongoing genetic improvement program on the West Coast of the United States using amplified fragment length polymorphism (AFLP) markers. All but one of the naturalized populations in both the USA and New Zealand are genetically more similar to native populations from the Ariake Sea (Midori River) than to the Miyagi region of their origin, but all domesticated stocks more closely resemble the wild Miyagi population. According to local oyster producers, the one exceptional naturalized population (Tillamook) is a very recent colonization derived from farmed oysters. Such consistency is unexpected under random genetic drift, and I speculate that both natural and artificial selection may have altered AFLP allele frequencies in this species in the course of naturalization and domestication.

Tilapia species are able to hybridize in captivity or in natural conditions following introduction of alien species. Here, we report a case of hybridization between two (and perhaps three) autochthonous species, Tilapia zillii and T. guineensis, resulting from a modification of their environment due to human activities. The man-made dam Ayamé (Côte d'Ivoire) transformed the River Bia into a lake (Lake Ayamé, area: 197 km2). In this new environment, both tilapia species have hybridized. In order to study hybridization along the Bia System, 25 allozyme loci have been screened in 470 specimens from ten locations. Two loci LDH-1 and PGI-2 were diagnostic between the two different species and can be used to identify hybrids in each sampling location of the River Bia basin. The percentage of pure T. zillii individuals in Lake Ayamé varied from 18.1% in Ebikro to 4.2% in Kétesso while percentage of pure T. guineensis varied from 81.3% in Yaou to 50.0% in Ebikro. The proportions of hybrids varied from 8.3% in Yaou to 31.9% in Ebikro. The existence of private alleles observed in tilapia from Lake Ayamé compared to what has been observed in both reference populations, T. zillii and T. guineensis led to the hypothesis that a third species could have been engaged in this hybridization. This third species is likely to be T. busumana, formerly present in the lake but now rarely observed. If this natural hybridization is due to the dam construction and the correlated ecological changes, then other hybridizations could result since many dams have been constructed within the range of these species in Côte d'Ivoire.

The direct amplification of length polymorphism technique (DALP) has been used to distinguish species-specific banding patterns in two marine gastropod oyster drills Ocenebra erinacea (Linnaeus, 1758) and Ocinebrellus inornatus (Récluz, 1851). Ocenebra erinacea is the European oyster drill, common along all European coasts. Ocinebrellus inornatus, the Japanese oyster drill, was recorded in oyster growing areas of the Marennes-Oléron Bay (SW France) for the first time in 1995. This new biological invasion could lead to an increase, which must be evaluated, in the predation risk for cultivated species i.e. oysters and blue mussels, and for littoral fishing resources along the French Atlantic coasts. As a result, since specific identification of early life stages of both species (egg capsules and juveniles) was previously found to be both difficult and unsure using only morphological criteria, four Ocenebra erinacea and two Ocinebrellus inornatus specific molecular markers were identified and sequenced. These markers will facilitate the assessment of respective ecological impacts (reproductive patterns, abundance and spatial distribution of juveniles), resulting from the exotic species versus the native species and will allow us to analyse with certainty demographic profiles of the two oyster drill populations.

Trois niveaux trophiques ont été expérimentalement étudiés chez le silure africain Heterobranchuslongifilis. Au cours d'un 1er essai, des poissons d'un poids moyen initial de 60 g ont été rationnés (1 % du poids vif) pendant trois semaines puis alimentés pendant 3 semaines soit ad libitum soit à 3 % du poids vif. Leur croissance a été comparée à celle de poissons nourris en permanence soit en excès soit à raison de 3 % du poids vif. Si le poids vif final des lots ayant subi une restriction est inférieur à celui de leurs homologues alimentés à taux constant, les résultats indiquent que la restriction alimentaire induit ultérieurement une croissance spécifique significativement supérieure, et un indice de consommation meilleur. Cette croissance compensatrice est due à la fois à une hyperphagie et à une amélioration du métabolisme. Un effet positif de l'hyperphagie est encore noté pendant les deux semaines suivantes. Lors de la 2e expérience, des silures d'un poids moyen initial de 141 g ont été nourris pendant 10 semaines soit à un taux constant de 4 % du poids vif, soit alternativement à un taux de 2 % du poids vif pendant une semaine, puis alimentés pendant une semaine à raison de 4 ou 5 % du poids vif. Au terme de l'essai, les poids moyens ne sont pas significativement différents. Les indices de consommation les meilleurs (1,79) sont notés pour les poissons ayant subi l'alternance avec un niveau haut analogue au témoin (45 %). Lors d'une 3e expérience, des silures, d'un poids moyen initial de 340 g ont été nourris pendant 5 mois, soit au taux constant de 3 % du poids vif, soit de façon alternée à 2 et 4 % du poids vif sur la base d'un pas de 15 jours en tenant compte des phases lunaires. Au terme de l'expérience, les poids moyens finaux ont varié de 977 à 1 127 g, tandis que les indices de consommation variaient de 2,1 à 2,5. Les meilleures performances, pour l'ensemble des critères utilisés sont notées pour les lots nourris à 2 % du poids vif en lune descendante, puis à 4 % en lune montante. Chez les poissons nourris de façon restreinte, en période de lune montante, la croissance est minimale. Pour valoriser le phénomène de croissance compensatrice ainsi mis en évidence chez le silure on peut recommander une restriction alimentaire, durant des périodes de 1 semaine. En revanche, tirer bénéfice de l'hyperphagie ne semble pas profitable.

Even when fishing effort data are not available in a developing fishery, it is often still possible to develop a simple fishery indicator to obtain information about the status of the stock. Using catch data only, Grainger and Garcia, (FAO Fish. Tech. Pap. 359, 1996) showed that the changes over time in the relative rate of catch increase (RRCI) can be used to detect when a stock reaches its over-fishing level, i.e., the year when RRCI falls to zero. The method presupposes that fishing effort increased steadily over the period concerned. We propose a generalization of this method that consists in obtaining a crude estimate of the maximum sustainable yield (MSY) by plotting the trend in catches against the smoothed RRCI. The yellowfin tuna (Thunnus albacares) fishery in the Eastern Atlantic was used to show the bold relationship between MSY estimates obtained from standard equilibrium production models and from this method. Given that it is very difficult to estimate effective fishing effort for skipjack tuna (Katsuwonus pelamis), we show how this simple fishery indicator can be used to obtain proxies of MSY for skipjack fisheries located in the Eastern Atlantic Ocean and in the Indian Ocean.

A statistical approach to evaluate the temporal trends in the abundance of female Centroscymnus coelolepis in Portuguese waters of ICES division IXa is presented. A state space model is used, which integrates all the available information of the species’ life history as well as knowledge of its biological dynamics. The model involves two processes that run in parallel: a non-observed process (the state process) that describes the annual female population abundance and an observational process of annual fisheries catches in numbers, assumed to be measured with error. Estimation is done within the Bayesian paradigm using sequential importance sampling with resampling. To evaluate the sensitivity of the model to the prior distributions chosen for the parameters, three scenarios with different levels of prior information were considered. Trends in population abundance level and the abundance levels themselves are quite similar in the two scenarios using biological information, but the model that incorporated all the available biological information in the priors provided the best fit to the observed data. The results indicate that taking into account the main biological drivers and the fishing information in the same state space model provides a coherent picture of the population abundance trends, further suggesting that the fishing impact on the population inhabiting Portuguese mainland waters was low.

Based on an extensive literature search, the present overview discusses the economic relevant diseases of Siluroidei, cultured for human consumption. One herpes virus and two irido viruses play a significant role for channel catfish (Ictalurus punctatus), sheatfish (Silurus glanis ) and yellow bullhead (1. melas )culture, respectively. There is only one fish species-specific bacterial disease which has an economic impact in the catfish industry: Edwardsiella ictaluri. Secondary infections with opportunistic bacteria and fungi are of interest in all catfish species cultured both under intensive and extensive circumstances. Etiology, pathology, prevention and treatment are shortly discussed for all diseases. Also some diseases of unknown etiology, which occur in African (Clarias gariepinus ) and Asian (C. batrachus ) catfish, are described.

When measuring the flux of migrating salmon in rivers there are often multiple fish in the beam simultaneously. To obtain accurate measurements of flux, an understanding of the effects of multiple targets is required. Multiple targets in various configurations were passed through a horizontally-oriented 4° × 10° beam from a split-beam echo sounder. The effects on target strength, detection probability, spatial and temporal patterns of echoes, and measurement of target position are presented. When multiple targets were in the beam at the same range, the target strength was positively biased, whereas, when they were in-line at different ranges, the target strength and detection probability were negatively biased for the shadowed targets. Targets at the same range, but separated in the vertical or horizontal direction, produced characteristic patterns in the X vs. ping and Y vs. X plots. Similar patterns were found in routine observations of migrating salmon, allowing the identification of some multiple-target events. Identification of these events can aid in the correct interpretation of migrating fish data for flux measurement.

Five polymorphic microsatellite DNA loci were identified in Labeo dero (Hamilton Buchanan), through cross-species amplification. Thirty-one primers developed for three cyprinids were tested in the study. The genetic variation detected at each polymorphic microsatellite locus was analysed. Significant genotype heterogeneity indicated that the samples are not drawn from same genepool. The identified microsatellite loci exhibited promise for use in fine scale population structure analysis of L. dero.

A hydroacoustic monitoring program for migratory herring was conducted in Drogden Channel, near Copenhagen, Denmark, beginning in June, 1996. Using installations of 100-kHz sidescan sonar oriented across the channel, herring schools were observed at ranges up to 500 m in water depths of 10–14 m. In October 1997, this effort was supplemented with a 12-kHz sidescan mounted on a motorized tripod allowing azimuthal sector scanning. This 12-kHz sidescan was able to detect herring schools up to a 1200-m range. Two examples are examined to assess the limits of herring school detectability and the feasibility of abundance estimation. In both cases, herring schools are detectable by their transience and up to 20 dB signal excess relative to the nominally stationary background reverberation, dominated by seabed backscattering. Attempts are made to extract quantitative abundance estimates using methods based on school size and density, and through quantitative echo-integration. Acoustic ray tracing was found to be useful in interpreting the results, and in particular modeling boundary-reflection focusing as a potential source of positive bias in herring abundance estimates.

In order to protect and sustainably manage fishery resource species, it is essential to understand their movements and habitat use. To detect the hypothesised migration of maturing veined squid Loligo forbesi from the west coast of Scotland (UK) to the North Sea and identify possible inshore-offshore movements, we analysed seasonal, spatial and environmental patterns in abundance and size distribution, based on commercial fishery landings data and trawl survey data from Scottish coastal waters (International Council for the Exploration of the Sea, ICES areas IVa, IVb and VIa). A geographic information system (GIS) was used to build monthly contour maps of abundance. Generalised additive mixed models (GAMM) were used to quantify patterns in size distribution and abundance. In most years, there was no evidence of movement from the West to the East coast of Scotland. Evidence of inshore-offshore movements during the life-cycle of the cohort that recruits in autumn (winter breeders) was found instead. The winter breeding cohort appears to spawn in inshore waters and some evidence suggests that the spawning grounds of the summer breeders are also inshore. Across seasons, higher abundance of L. forbesi can generally be found in the north of Scotland at intermediate water depths and in warmer waters.

Cette étude a pour objet le développement de la pêche artisanale dans un petit pays insulaire de Polynésie occidentale. La modernisation de la petite pêche et l'accès à la pêche au large contraignent les pêcheurs à une nouvelle gestion des moyens de production, de l'espace, du temps et de l'argent fondée sur des valeurs occidentales qui sont en contradiction avec l'environnement socio-culturel traditionnel. Des contraintes dues à un héritage ethno-historique ancestral constituent un frein au développement et à l'assimilation de nouveaux moyens de production. L'enquête a été menée au coursd'un séjour de deux mois aux îles Tonga en 1987, précédé de deux missions de chacune six mois en 1974 et 1983 consacrées à l'étude des techniques rituelles de pêche en les insérant dans une analyse globale de la société.