Bahía Magdalena, located on the southwest coast of Baja California Sur, Mexico (24°20'N, 111°30'W), is an important area for fishing of small pelagic fish. The Pacific sardine (Sardinops caeruleus) comprises more than 75 % of the total catch in the bay. Hydro-acoustic surveys were carried out in this bay using a single-beam echo sounder, Simrad EY-200 (200 kHz), during three oceanographic surveys (March, July and December 1996). Results demonstrate that in July more than 75 % of the positive observations (those echograms with more than 100 echoes in the volume sampled) and most of the echo counts were recorded in the 5–10-m-deep layer. During March and December, positive echograms in the upper stratum were below 50 % and most of the echo counts were detected in the lower layer (10–20 m). These results were related to the availability of Pacific sardine to the commercial fleet, specifically to the capture-per-unit-effort. Results support the hypothesis that sardines migrate during late summer and autumn and that a new recruitment occurs during the winter within the bay.

La dynamique de production du rotifère Brachionus calyciflorus en conditions contrôlées et sa qualité nutritive en tant que source alimentaire pour les larves de poissons d'eau douce sont évaluées après une détermination du taux de développement de cet organisme sur l'algue Dictyosphaerium chlorelloides. Ces aspects sont examinés par le biais d'une série d'études portant sur la dynamique de population (taux de production journalier, durée de développement embryonnaire et temps de génération minimum, fécondité des femelles amictiques) et sur la composition biochimique de ces organismes. La durée de développement embryonnaire, fortement dépendante de la température, varie entre 7 et 13,4 h. Les rotifères atteignent leur meilleur taux de reproduction à 25 °C, soit en moyenne 22,1 œufs par femelle. L'origine des femelles utilisées (jeunes femelles amictiques ou femelles précultivées sur D. chlorelloides) influence les résultats de production en masse, avec des densités atteignant, en fin de production, respectivement 245 et 188 rotifères par ml. En ce qui concerne la qualité nutritionnelle des rotifères, la teneur en protéines brutes varie peu au cours du cycle de production (53,5–54,1 % de la matière sèche). Parmi les acides gras, l'acide linoléiqueC18:2n-6 est le plus abondant dans les rotifères, et représente, en fin de cycle de production, 42 % des acides gras identifiés chez les femelles précultivées sur D. chlorelloides.

Strategies for biomass control are actively sought in response to proliferation of the introduced, suspension-feeding gastropod Crepidula fornicata along European coasts. Among these, dredging, crushing and on-site rejection may only be envisaged if the risk of further dissemination through the release of gametes and of excapsulated embryos/larvae is found to be nil or extremely low. This study evaluates such risk using three approaches: (1) determination of the periods of brood presence/absence, (2) external fertilizations of gametes obtained by gonad stripping, (3) cultures of mechanically-excapsulated embryos and larvae. A period of near- or total brood absence was observed between September 2006 and January 2007. The few zygotes (1.5% to 7.5%) obtained from external fertilizations did not proceed beyond the 4-cell stage. Excapsulated young embryos and mid-stages died in less than 4 days of culture. Despite their ability to swim, grow and feed, excapsulated veligers all died before metamorphosis. No juveniles were obtained from external fertilizations and excapsulated cultures, indicating that the release of crushed catches directly at sea could not present a dissemination risk from the standpoint of gamete or prematurely-excapsulated larval dispersal. Furthermore, by carrying out the crushing operations during the period of brood absence, the dissemination risk becomes nil. Negative ecological impact of such operations could be offset by attraction of motile predators, as yet unaccustomed to this introduced species, and their subsequent generalization to live slipper limpets and invasive feral Crassostrea gigas. At the very least, this biomass reduction approach would concentrate bottom habitat unavailability to restricted zones, freeing up the rest of the subtidal for other, formerly displaced species, as well as reducing the pressure on the trophic carrying capacity of affected habitats.

Replacing aquaculture feeds based on fisheries-derived resources with plant-based dietscould be a relevant strategy to improve the sustainability of aquaculture. Recent studieson sea bass have shown that the total and early replacement of marine products by plantproducts would have a moderate effect on fish growth and body lipid content. Whether aplant-based diet impacts behavioural and physiological traits possibly linked to fishwelfare, is not known, however. Here, we studied the effect of a totally plant-based dietintroduced at an early stage of sea bass development on self-feeding behaviour, learningability in a T-maze and stress biomarkers. We first compared learning processes inself-feeding conditions, between naive fish fed a plant-based diet (PBF) and fish fed aclassic marine diet (MF). Then, we tested fish individually in a T-maze to compare the twofeed groups for swimming activity, exploration and the ability to learn to discriminatebetween two two-dimensional objects associated with a reward. Blood physiologicalvariables, including stress indicators (cortisol and glucose concentrations), were alsodetermined. We did not find any indications of differences in self-feeding behaviourbetween PBF and MF in the first 30 days. A second experiment showed similar swimmingactivities in both fish categories. The “no-choice” percentage was high in both fishcategories (~60%), but all the fish moved preferentially toward the reward. Theirfirst turns indicated an ability to discriminate between two two-dimensional objects tocomplete a simple task. However, the high percentage of “no-choice” responses in both fishcategories could have rendered the results non significant. The T-maze test procedureinduced the production of high concentrations of cortisol, indicating acute stress in fishof both groups during testing. Plasma cortisol concentration was higher in MF than PBF,suggesting that the plant-based diet may affect the short-term release of cortisol. Thisstudy provides the first insight into the impact of a plant-based diet on sea bassbehavioural traits, and confirms the effect of this diet on cortisol release in responseto stress. Overall, in this first experiment, we did not find any major impact of aplant-based diet on sea bass behavioural traits, which is an interesting point for thedevelopment potential of such a sustainable aquaculture strategy.

Genetic differentiation was studied among Leporinus friderici, L. granti, L. lebaili and L. affinis steyermarki, neotropical fish of the anostomid family found in French Guiana, using starch-gel protein electrophoresis. Fifteen enzymatic proteins representing twenty loci have been screened. This revealed marked genetic differences between these species, which are hardly morphologically discernable and indicates they are reproductively isolated. Diagnostic loci for unequivocal species identification have been found and will allow establishment of pure breeding stocks for planned aquaculture of Leporinus species.

Catch rates (kg hour−1) of horse mackerel (Trachurus trachurus), blue whiting (Micromesistius poutassou) and hake (Merluccius merluccius) from a series of 22 groundfish surveys conducted off Portugal between 1989 and 1999 were analysed using integrated logistic and gamma Generalized Linear Models (GLM). This methodology deals with the large amount of zeros in survey data matrices by modelling the probability of catch and the amount of positive catch separately, and then integrating the two sub-models into a single catch rate model of abundance. Among the explanatory variables included in the models, the geographic areas occupied by fish assemblages, i.e., groups of persistent co-occurring species, explained most of the variability observed for horse mackerel and blue whiting, while depth was the most important factor for hake. Because of hake's ubiquity on the Portuguese margin, models for this species were less parsimonious and explained a lower proportion of total variability compared with the other species. The abundance of horse mackerel is much higher in the winter and reduces with depth. Blue whiting and horse mackerel exhibited opposite trends in abundance from 1991 to 1994, with the latter species presenting a higher abundance throughout this period. No clear temporal trends of abundance were detected for hake. The effect of trawling hour in models suggested that horse mackerel and blue whiting exhibit vertical migrations, staying close to the bottom by day, when abundance is higher. The current approach proved to cope well with sparse catch data matrices and brought out novel information on the ecology of fish species in the Portuguese continental margin by successfully integrating environmental information into the analysis of fish abundance.

An image discrimination technique was developed to improve specific identification of some toxic Dinophysis cells (marine dinoflagellates involved in diarrhoeic shellfish poisoning), especially the "acuminata" and "sacculus" groups, which can be present at different ratios in natural sea-water samples collected during toxic episodes. This work was performed with image analysis software SAMBA (TITN Alcatel) using preserved cells directly observed through an inverted microscope and recorded with a video camera before further processing. All morphometric parameters used for discrimination of 7 different species or morphotypes of Dinophysis were tested with discriminant analysis. This study indicates that Dinophysis sp. and D. pavillardi seem well classified at the species level, whereas D. cf. acuminata and D. sacculus appear to be morphotypes of D. acuminata.

L'étude des carnets de pêche des marins-pêcheurs et l'échantillonnage des captures ont permis de cerner les caractéristiques biologiques des populations de grandes aloses (Alosa alosa L.) prélevées sur l'Adour de 1988 à 1991 et d'étudier l'influence des conditions hydroclimatiques sur le niveau moyen des captures journalières par sortie. Les aloses sont principalement recrutées dans l'estuaire entre le début du mois d'avril et la fin du mois de mai: entre 78 et 89 % selon les années. Les mâles sont en moyenne plus jeunes et à âge égal plus petits et moins lourds que les femelles. Ces résultats confortent les connaissances obtenues sur les principaux stocks français qui remontent les systèmes fluviaux de la Loire et de la Gironde. Les analyses effectuées soit par l'Analyse Factorielle des Correspondances soit par l'utilisation du Modèle Linéaire Généralisé indiquent que les variations conjuguées du débit fluvial et du coefficient de marée ont une influence sur l'abondance des captures journalières exprimées en kg par sortie. Le travail réalisé à l'aide de ces deux méthodes complémentaires d'analyse permet à la fois de décrire et de quantifier les liens entre les captures par sortie (CPUE) et les facteurs hydroclimatiques. En effet, une augmentation de ces CPUE est constatée avec l'accroissement des coefficients de marée, le débit fluvial intervenant comme facteur de modulation secondaire.

During a SCUBA survey on herring spawning beds on and near Fisherman's Bank (NAFO Div.4T) conducted in September 1985, divers observed a spawning bed with heavy egg depositions, whichfrequently reached thicknesses between 20 to 30 layers. Continuous egg carpets of this thicknessextended over an area of approximately 200 × 500 m. Most of the egg mass on this spawning bed wasin a state of deterioration, showing mass mortality and extended fungi coverage.

Egg samples taken from various layers showed that almost all eggs were fertilized. Live egg batches were incubated for further observation. Embryos were found to be in various developmental stages. The rate of development was obviously related to the position within the egg mass. Many embryos from the surface appeared to be normal. All eggs located below the second layer exhibited embryoswith various malformations.

Egg samples did not show any evidence of the presence of Ichtyophonus, a known fungal disease in herring. None of the isolates obtained are known to be pathogenic to fish eggs. The observed mass mortality of herring eggs on the spawning bed was mainly caused by spontaneous intensive mass spawning leading to an unusually dense packing of the deposited eggs and therefore not permitting sufficient separation for water exchange and oxygen supply.

Environmental factors accompanying such spontaneous mass spawning are not well understood.Vertical temperature profiles from nearby locations showed sudden sub-surface temperature changescoinciding with the time of spawning. Meteorological conditions indicated wind-related water displacement near the spawning bed. While no drastic change in temperature was observed near the surface, changes of about 8 °C occurred in one day, at 20 m depth. These events may have triggered the mass spawning in a restricted area, later resulting in heavy mortalities when embryos reached advanced developmental stages requiring substantial oxygen supplies.

Bivalve molluscs survive lack of oxygen and may present cellular characteristics allowingtolerance to oxygen deprivation. The objective of the present work was to determine invitro responses of circulating cells (i.e., hemocytes) of Pacific oyster,Crassostrea gigas, to oxygen deprivation by analysis of mitochondrialmembrane potential (ΔΨm) and reactive oxygen species (ROS) production.Hemocytes submitted to oxygen deprivation showed a reduced ROS production and an increasedΔΨm. Confrontation of present results with recently reported findingsallows us to hypothesize the existence of an alternative mitochondrial reductase, and theinvolvement of mitochondrial potassium channel in maintenance of ΔΨm.Tolerance of bivalve hemocytes to variable oxygen availability appears, at leastpartially, related to mitochondrial specificities.

Outre Clarias gariepinus introduit en pisciculture au début des années 1970, d'autres poissons-chats (Siluroidei) africains ont vu leurs potentialités aquacoles faire l'objet d'une évaluation approfondie depuis une quinzaine d'années. Il s'agit des espèces appartenant aux genres Chrysichthys (Claroteidae) et Heterobranchus (Clariidae) étudiées principalement en Côte d'Ivoire, au Nigeria et au Bénin, et pour l'essentiel dans le cadre d'une aquaculture en milieu lagunaire ou estuarien. C'est en Côte d'Ivoire, au début des années 1980. que la reproduction de Chrysichthys nigrodigitatus, puis celle de Heterobranchus longifilis, a été obtenue pour la première fois en captivité suite aux travaux conduits par le Centre de Recherches Océanographiques d'Abidjan. Depuis, les cycles d'élevage des ces deux espèces ont été maîtrisés et un premier transfert vers le développement effectué. La pisciculture de C. nigrodigitatus est principalement monospécifique, de type intensive ou semi-intensive, en enclos lagunaires (Côte d'Ivoire) ou en étangs saumâtres (Nigeria). En Côte d'Ivoire (lagune Ebrié), le développement de son élevage se concrétise depuis 1991 par une production annuelle de l'ordre de 200 à 300 tonnes. H. longifilis présente une biologie très similaire à celle de C. gariepinus, mais avec l'avantage d'une croissance plus rapide. La production commerciale de cette espèce s'amorce actuellement en Côte d'Ivoire. L'élevage de type intensif en enclos lagunaires semble constituer l'une des voies appropriées pour le développement de l'élevage de ce poisson ; mais sa pisciculture en étangs d'eau douce connaît également des résultats encourageants. A partir de l'expérience ivoirienne, des projets de développement de l'aquaculture de H. longifilis sont en cours de réalisation au Niger et au Cameroun. La littérature récente fait également état d'élevages expérimentaux de H. bidorsalis au Nigeria. Des hybrides entre H. longifilis ou H. bidorsalis et C. gariepinus ont été produits en Afrique du Sud. en Côte d'Ivoire et au Nigeria. Toutefois, l'intérêt réel de l'utilisation de ces hybrides en aquaculture en comparaisn des espèces parentales reste à démontrer. Les résultats obtenus en Côte d'Ivoire indiquent que C. nigrodigitatus et H. longifilis constituent désormais une possibilité de diversification de la production, voire une alternative à l'utilisation de C. gariepinus, pour la pisciculture africaine. Une synthése des données existantes sur la biologie et l'élevage de ces espèces est présentée.

Milling behaviour is problematic when using hydroacoustics to estimate the number of migrating fish in rivers. Milling behaviour was observed for adult sockeye salmon migrating upstream in the Wannock River, to their spawning grounds in the tributaries of Owikeno Lake in the central coast area of British Columbia, Canada. We classified the acoustic salmon tracks to separate the milling fish from the actively migrating fish in an attempt to obtain an estimate of sockeye salmon flux as they migrate to their spawning grounds. We used discriminant function analysis and found that three variables measured on each track were sufficient for the classification of the acoustic tracks into milling and non-milling categories with an approximate classification accuracy of 98%. The method we present can also be used to separate tracks of targets of interest from noise or debris tracks that occur in the acoustic data, if discrete track characteristics are ascertained.

There is growing interest in bio-economic models as tools for understanding pathways of fishery behaviour, in order to assess the impact on natural resources. Based on ‘FishRent’, a modelling approach is presented that integrates economics of the fleet, the impact of fishing on stock development and their spatio-temporal interplay. The simulation of species seasonal movements in combination with both observed values and stochastic recruitment allowed analysing the economic response of fleet segments to changes in stock distribution and development. Optimisation of net profits determines the effort adjustment and spatial allocation of fleet segments, which in turn affects the level of catch rates. Effort tended to concentrate where fish abundance was high, but also where fishing costs were low. In simulations with the current management plan spawning stock of North Sea saithe (Pollachius virens) declined below its precautionary reference point. In response fishing far from home ports became expensive and 40% of the initial effort was shifted to areas closer to home ports, but as areas of high fish concentrations were located by the modelled fleet segments catch rates remained high. Changes in seasonal/annual stock distribution, the stock decline and costs influenced the change in fishing effort distributions leading to overestimated catch per unit of effort values that masked the decline of stock abundance.

This study relied on the day-by-day analysis of bioenergetics and prey size preference inisolated cannibals of the African catfish Heterobranchus longifilis(13–57 mm standard length, 3–500 mg dry body mass, n = 153) that were offeredad libitum conspecific prey of adequate sizes in small-sized (2-L)environments under controlled conditions (12L:12D, 30 °C). In these conditions, cannibals ofincreasing body size selected preferentially prey of decreasing size relative to theirown, and increasingly closer to the optimal prey size (producing the highest grossconversion efficiency). The role of experience in cannibalism was found of secondaryimportance relative to body size, both as regards food intake and prey size selectivity.These results indicate that in environments that minimize the escape capacities of theirpotential victims, as applies to most aquacultural contexts, fish exercising cannibalismtend to forage optimally, which has rarely been evidenced for piscivorous behaviour. Thepresent study further highlights that H. longifilis possesses a very highcapacity for growth, which originates from the combination of high food intake and veryhigh conversion efficiency, and makes this species of utmost interest for aquaculturistswherever fast growth is desirable, but also extremely prone to cannibalism whereverfeeding schedules are inadequate.

The pathology of farmed tilapias is reviewed from presently available published data. The effects of intensive production systems on the aspects and importance of pathology are outlined. The main pathogenic organisms are recorded. For the moment, these pathogens seem to represent a potential threat, rather than being primary causes of losses. Conversely, environmental factors together with practical errors resulting from a lack of biological and zootechnical data on tilapias, seem to be responsible for most of the difficulties which are encountered. In the short term, intensive research in genetics, nutrition and zootechny should result in significant health improvements for tilapias.

En julio de 1989 y 1990 se hicieron dos cosechas comerciales de Gelidium sesquipedale mediante arranque y corte, con objeto de observar la recuperación, obteniendo datos que sienten las bases biológicas para establecer un plan de gestión del recurso.

Se observa una reducción de la biomasa del 80 % tras la cosecha, no variando la densidad de frondes y reduciéndose la talla media de la poblacion un 48 % por corte y un 31 % por arranque. Los 3 ó 4 meses que siguen a la cosecha son muy importantes en la recuperación de la biomasa, de manera que en octubre ya no existen diferencias significativas entre las medias de las zonas cosechadas y control. En este período, frente a tasas de crecimiento nulas en la zona control, se obtienen valores alrededor de 1.3 %.día−1 en las cosechadas, mientras que entre marzo y julio oscilan alrededor de 0.9 %.día.−1.

La producción es 1.4 veces mayor en las áreas cosechadas (valores alrededor de 1 100 g.m−2.año−1), mientras que las tasas de renovación son 2.5 veces mayores en ellas (6.8 año−1).

Los epífitos prácticamente desaparecen tras la cosecha, pero se recuperan al mes siguiente, no aumentando su biomasa en relación a la de la control.

Depuis 1987, la maladie de l'"anneau brun" provoquée par une bactérie pathogène du genre Vibrio, dite Pl, atteint les élevages de palourdes japonaises Ruditapes philippinarum des côtes atlantiques françaises. Les expériences réalisées en laboratoire montrent que chez des palourdes contaminées expérimentalement avec Pl, 92 % des individus laissés à jeun sont atteints tandis que seuls 60 % des individus nourris développent la maladie. La mortalité imputable à la bactérie est diminuée de 40 % chez des individus nourris. La nutrition semble constituer un moyen de lutte contre l'action de la bactérie. Une étude comparative de la glande digestive d'animaux sains et contaminés apporte des éléments sur les stades digestifs des tubules. L'étude des rapports de la lumière tubulaire sur la section entière des tubules permet de déterminer une échelle standard des stades digestifs. Les proportions des stades varient suivant l'état de l'animal. Chez un individu atteint, le taux des tubules au stade de dégénérescence triple au détriment des stades d'absorption qui n'apparaissent plus. Les palourdes infectées ne montrent aucune différence significative qu'elles soient nourries ou à jeun contrairement aux individus témoins où le stade d'absorption voit sa proportion augmentée et les stades 3 et 4 diminués en présence de nourriture. Le cycle de digestion est perturbé et la glande digestive entredans un état général de dégénérescence. La mise au point de cette technique devrait permettre de visualiser automatiquement l'état de la glande digestive d'individus du milieu naturel ou d'élevage.

Socio-economic characteristics such as age, gender, educational attainment, employment status, and income contain vital information about how an industry may respond to changing circumstances, and hence are of importance to decision makers. While some socio-economic studies exist, relatively little attention has been given to fishery and aquaculture industries in regards to their socio-economic profiles and their role in the development prospects of these industries. In this study, by way of example, we focus on Australia’s Sydney rock oyster (Saccostrea glomerata) (SRO) industry. The aim of this study was identify the socio-economic profile of the SRO industry and to illustrate the value of such information for an industry management assessment. The SRO industry has experienced a major decrease in production volume since the late 1970 and continues to be affected by prevailing diseases and increasing market competition from Australia’s Pacific oyster (Crassostrea gigas) industry. It is likely that socio-economic aspects have influenced this development within the SRO industry. The socio-economic profile was developed using data from a SRO industry farm survey which was undertaken in 2012. Findings suggested that this industry is characterised by a mature aged oyster farmer population and a part-time oyster farming approach. These characteristics may affect the farmers’ ability to drive innovation and growth. The results also suggested that there may be potential industry entry barriers present in the SRO industry which may prevent younger people taking up oyster farming. Given the results, the study concluded that the current socio-economic profile of the industry has likely contributed to the present economic status quo of the industry.

In order to highlight the main factors accounting for the growth of clams in Marennes-Oléron Bay, three locations were investigated in 1984-85. First, factor analysis provided information on fluctuations of the environment. Second, principal components analysis was used to study ecological phenomena. The main axes explained the growth rate, which was included in an allometric model. Its properties were then studied by means of sensitivity analysis.