We used a digital stereo-video camera system for three-dimensional monitoring of cultured Pacific bluefin tuna, Thunnus orientalis, swimming freely in a net cage. We estimated the fork length and length frequency distribution of individual fish using the direct linear transformation (DLT) method. Information obtained from stereo images is useful for managing the growth of tuna during rearing. Our aim was to develop a simple method involving a combination of DLT and commercial image-processing software to enable aquaculturists to obtain three-dimensional measurements of fish. In this study, we used a stereo-video camera system to evaluate the precision and validity of fish size estimates determined from repeated measurements. Of the total assessed individuals swimming within a distance of  <5.5 m from the camera system, estimates for 99% (106/107) were found to be valid, with an error ratio (standard error/mean) of  <5%. Therefore, we believe that our proposed simple method for monitoring free-swimming fish could be very useful for aquaculture management.

A number of feedstuffs was tested to obtain the apparent digestibility coefficients (ADC) of dry matter, protein, energy and phosphorus for seabass juveniles (individual mean weight of 40 g). The effect of the inclusion level (15 and 30 %) of a feedstuff in a reference diet on the ADC was also evaluated. The feedstuffs tested in this trial were two fish meals, a fish protein hydrolysate, blood meal, meat meal, soybean meal and yellow dextrin. The ADC of dry matter were consistently lower than those of energy, but there was a significant positive correlation between them. The ADC of protein were high (range 89−97 %) in all feedstuffs. The ADC of energy of animal feedstuffs (range 86−96 %) and dextrin (93 %) were also high, while that of soybean was lower (70 %). The ADC of phosphorus of animal feedstuffs averaged 81 % whereas that of soybean was only 38 %. There were no significant differences in the ADC of protein and energy of each feedstuff at the two inclusion levels tested.

The histological development of the digestive tract in hatchery-reared green sturgeon (Acipenser medirostris) larvae and the effects of food deprivation on the digestive system organization were studied from hatching until 31 days post-hatching (dph). At hatching, the larval digestive system consisted of two rudiments: a large endodermal yolk sac and a primordial hind-gut. During the endogenous feeding phase, the wall of the yolk sac differentiated into the stomach (glandular and non-glandular regions) and the anterior and intermediate intestine, while the hind-gut primordium differentiated into the spiral valve and rectum. At the onset of exogenous feeding (15 dph at 16 °C), the organization and cytoarchitecture of the digestive system in green sturgeon larvae was generally similar to those of juveniles and adults. Larvae deprived of food exhibited a progressive deterioration, with subtle pathological changes observed after 5-d starvation: shrinkage of digestive epithelia, tissue degeneration, and necrosis were observed at 10–15 d of starvation (30 dph). No changes were observed in the mucous secretion of different regions of the digestive tract of food-deprived larvae. The histological analysis of the larval digestive system may be used to evaluate the nutritional condition of larval green sturgeon in their nursery habitats in spawning rivers, which are affected by dams and flow diversions.

A 3-year survey was made of several biological markers in mussels (Mytilus edulis) exposed in situ to the oil that came ashore after the wreck of the “Erika” tanker on the Brittany (France) coast in December 1999. The mussel response was assessed using a set of 7 biomarkers, most of them related to the metabolism of organic contaminants. After a series of validation tests, data was evaluated for only 5 biomarkers: acetylcholinesterase (AChE), glutathione S-transferase (GST), catalase (CAT), malondialdehyde (MDA) and deoxyribonucleic acid (DNA) adducts. No significant reductions in GST or CAT levels were observed, levels of DNA adducts and MDA were high during the 6 months immediately following the accident and levels of AChE were significantly lower during the first year of the survey suggesting a general stress. A simple multivariate graphic method, the integrated biomarker response index, was used to combine 4 of the 5 validated biomarkers and quantify the degree of impact on mussels at different sites. The results show that mussel populations were affected by the oil spill only during the first year after the event.

At present, European marine fish farming is based on sea bream and sea bass. A trend for diversification is sustained by the diversity of environmental conditions, by the availability of new production techniques such as recirculating systems, by an increase in rearing yields, by new market trends and by the possibilities to reduce risks of disease outbreak. Already reared fish species were chosen considering a limited number of criteria such as a high selling price and the availability of juveniles or breeders in the wild. This paper proposes a new selection method of fish species as candidates for aquaculture development on the French Atlantic, the Channel and the North Sea coasts. Using a three-phase procedure, candidates were selected among 20000 fish species. Final classification was carried out using a panel of 22 criteria, taking into account inquiries conducted in France with aquaculturists but also with the main actors of distribution and transformation channels and with consumers. Cod (Gadus morhua) was selected by the present work as the first candidate for aquaculture development on the western coasts of France. This work also highlights the high interest of Gadoids for aquaculture development in this area.

Selectivity studies usually describe the effects on target species, whereas information on by-catch and discards is scarce. Nevertheless, large quantities of undersized individuals and invertebrates are discarded in the Mediterranean multi-species bottom trawl fishery. The present work analyses the data from two surveys carried out on the shallow and deep continental shelf (50–78 m, and 147–189 m, respectively) off the Balearic Islands (western Mediterranean). In these surveys, the traditionally used 40 mm diamond mesh codend and an experimental square mesh codend were used under commercial conditions. Catch composition, yields, size selectivity of both target and by-catch species, and discards were compared between the two mesh types. The mean selection length (L 50) clearly increased for most species when using square mesh, escaping many more individuals under their minimum landing size. Yield of Spicara smaris was significantly lower by using the square mesh, changing the composition of the retained catch. Escapement ratio and economic loss were significantly higher with square mesh, although economic loss was almost negligible for both meshes on the deep continental shelf. The use of square mesh significantly reduced the discards of algae in the shallow waters and fish on the deep continental shelf. The results confirmed that square mesh codend reduces the fishing pressure on small specimens as well as the impact of trawling on the ecosystem. These benefits would not lead to a reduction of the yields neither of the main target species, the fishes Merluccius merluccius, Mullus surmuletus, Zeus faber, and the cephalopods Loligo vulgaris and Octopus vulgaris, nor of the rest of commercial categories, except for Spicara smaris.

Eighteen spermiating males were randomly selected from a hatchery-reared stock and electronically tagged to record changes in their sperm quality parameters (spermatozoa morphology, ultrastructure and motility, ionic composition and osmolality of the seminal plasma, and sperm volume and density) during the spawning season. Stripping was performed at the beginning of March, April and May. The Barbus barbus spermatozoon has a head without acrosome, a midpiece with 4–6 mitochondria and proximal and distal centrioles, and a flagellum with the typical 9+2 pairs of microtubules. Apart from posterior width of the midpiece, morphological and ultrastructural parameters changed significantly during the reproductive season; generally by decreasing toward the end of reproductive season. Sperm volume also decreased from 0.42 in March to 0.15 ml in May, and density from 18.81 in March to 12.45 × 109 spz ml−1 in May. Osmolality (mOsmol kg−1) was 268 ± 4, 276 ± 2 and 268 ± 2 in March, April and May respectively. Chloride, sodium, calcium and potassium ion concentrations (mM) did not show significant differences between March and April (Cl−: 125.3 vs. 120.5, Na+: 75.7 vs. 69.7, Ca2+: 0.4 vs. 0.3 and K+: 84.7 vs. 84.0). The percentage of motile spermatozoa at 15 s post activation did not show a significant difference between dates, but the highest spermatozoa velocity at 15 s post activation was observed in April (91.4 ± 3.2 µm s−1) and then decreased significantly towards the end of the reproductive season (80.6 µm s−1 in May). However, lowest spermatozoa velocity was measured in March (70.4 ± 1.9 µm s−1). This study supports the hypothesis that longer spermatozoa swim faster. Within one stripping, velocity and percentage motility decreased significantly with time post activation. In conclusion, changes observed in B. barbus sperm parameters during the reproductive season, suggest there is association between such changes and spermatozoa aging processes.

Throughout much of the UK and in Europe generally the native oyster is in a severely depleted state in the wild. In order to address and potentially to reverse this situation Ostrea edulis was designated as a named species in the UK Biodiversity Action Plan as part of a national commitment to the International Convention on Biodiversity. Amongst other initiatives, some of which are summarised in this paper, a feasibility study was carried out to evaluate all the factors, including an economic assessment, relevant to a programme of stock restoration in the UK. The study showed that there is a considerable body of data on the biology, ecology and distribution of O. edulis to inform restoration projects. Appropriate legislation is in place to allow for restoration. Non-marketable costs and benefits were estimated. They provide an idea of the high value that may be placed on biodiversity aspects. Nevertheless, this study also shows that stock restoration can be commercially viable if fishery prices and yields are sufficiently high. Restoration efforts and associated studies elsewhere have shown the potential for success of native oyster stock regeneration, especially in disease-free areas. For these, there is a very strong element of re-creating and conserving an ecological resource. The relaying of cultch is seen as an essential component of a successful oyster restoration programme and the use of sanctuaries is generally considered beneficial. The loss of the standing stock is a limiting factor and re-stocking is an effective strategy. There is a basic genetic similarity of wild European O. edulis populations such that the source of stocks is not critical. There are some problems with hatchery rearing from these, but using breeding ponds or importing part-grown oysters are viable alternatives.

This paper reports a comparative study of two cupped oysters, Crassostrea gigas and C. angulata, and their hybrids reared in the Marennes-Oléron Sound (France) under usual farming conditions. The relative proficiency of these species was characterized in terms of growth, survival and reproduction, three major concerns for oyster farming. Four populations of each taxon were sampled (C. gigas: Japan and France; C. angulata: Taiwan and Spain) and used as progenitors to produce six different progenies under common hatchery and nursery conditions (transfer of 5 to 6 g of seed oysters at sea and rearing in bags for 2 years). Mortality profiles differed greatly among the progenies. The C. angulata progeny of Taiwanese origin gave the poorest results, with 100% mortality during the second year. For the entire rearing period, the highest yield (+22%) was obtained with the C. gigas progeny of French origin. The sexual maturation index, lipid cycles and dry weight loss after spawning showed that spawning of C. angulata was delayed by about two weeks compared to that of C. gigas. A clear maternal effect was observed for the growth and reproductive characteristics of the hybrids. On the whole, C. gigas of French origin gave the best aquacultural results. However, severe episodes of C. gigas mortality have been observed in France in recent years, indicating that this species might not be entirely suitable for sustained oyster farming in this country.

Differences in Mediterranean fish communities of two rocky coastal areas, one inside an integral marine reserve and the second outside the reserve, near Banyuls-sur-Mer, France, were compared using underwater visual census after a 12-year interval. In 1980, the community structure in and outside the marine reserve was studied at two depths (Bell, 1983). In 1992, We used the same methodology to assess if variations occurred in this fish community between these two samplings. In both 1980 and 1992, water depth affected the relative abundance of fish communities and the number of species was roughly maintained in both sites. However, there were several other important qualitative and quantitative variations in the fish fauna over this period: (1) The abundance of species has decreased in the integral reserve whereas it has been maintained outside the reserve; (2) Nine species are more abundant in the integral reserve and nine others are more abundant outside the reserve. Among the species vulnerable to fishing, such as Labrus merula, Symphodus tinca, Mullus surmuletus, Diplodus sargus, D. vulgaris, Scorpaena porcus, Oblada melanura, 6 of them are more abundant inside the integral reserve and 4 others are more abundant outside; (3) The demographic structure of vulnerable species inside the reserve has changed: only the proportion of large fish (30 to 40 cm length) compared to medium (15 to 30 cm) and small (0 to 15 cm) fishes was higher in the integral reserve. The prohibition of recreational and professional fisheries and scuba diving has the fish community in the integral marine reserve in 1992 enhanced less than in 1980. The impoverishment of the fish density in the integral reserve between these two periods is difficult to understand in regard to the stability of the fish density outside the reserve. These results stress the need for a more regular and more extensive survey of the fish assemblage in and around the marine reserve of Cerbère-Banyuls

In mollusc hatcheries and nurseries, live microalgae are traditionally used as feed for bivalves. Despite recent improvements in efficiency, such intensive culture of microalgae represents major cost factors in the production of bivalve larvae and spat. In an attempt to provide cost-effective alternatives and to simplify hatchery-nursery procedures, non-living algal food has been developed over the past few years. Substitution products such as bacteria, yeast, vitamin or docosahexaenoic acid enriched powders, dry and concentrated microalgae and microcapsules have been tested and evaluated on an experimental scale. The present article reviews major research aimed at developing non living diets in mariculture, which generally resulted in lower growth and higher mortalities than that recorded for controls fed live microalgae. At the present time, concentrated and dried microalgae appear to be the best alternative products for bivalves, for juveniles essentially, while microcapsules provide an excellent research tool to study their nutritional requirements.

Fish schools are known to take a large number of different shapes and dimensions, in such a way that defining a school from its morphology is still an unanswered question. Nevertheless, some school typology and classification has been done successfully in different areas of the world using vertical echo sounding data. This implies that some morphological patterns may correspond to or reflect behavioural specificities. The objective of this paper is to take advantage of the 3D exhaustive observation capabilities of multibeam sonar to extract the morphological and internal characteristics of tropical clupeid schools. The main parameters measured are geometrical properties (overall dimensions, volume, surface, etc.) and relative distribution of densities inside the school (heterogeneity, existence of nuclei, etc.). The main results show that a school is usually formed of one or several nuclei of high density connected by less dense parts, including empty areas (vacuoles). The dimension of these sub-units is highly variable, but remains inside a diameter of 5-20 m. The reliability of these dimensions is evaluated, and some thoughts on the behavioural mechanisms constituting schools are presented.

The quality of Moroccan Atlantic coastal wasters was monitored from 1993 to 1997 by measuring hydrological parameters (dissolved oxygen, suspended particulate matter, phosphates, and nitrates), and using the mussel Mytilus galloprovincialis as a quantitative bioindicator of cadmium, copper, manganese, and zinc contamination. Mean concentrations of dissolved oxygen and suspended particulate matter were indicative of the effects of urban and industrial discharges of wastewater, particularly at Mohammedia, Casablanca, Mehdiya, Jorf Lasfar and Safi. Stations receiving urban wastewater showed high nitrate concentrations, especially at Mehdiya, Rabat, Mohammedia, Casablanca and El Jadida. Metal concentrations in mussels showed significant variations depending on the station and sampling period. Jorf Lasfar and Safi had the highest mean concentrations for cadmium (8 and 7 μg·g–1 dry weight respectively) and copper (74 and 25 μg·g–1 dry weight). The relation between cadmium concentrations in mussels, and phosphate concentrations in water suggests that the processing of phosphate ores at these two sites is responsible for contamination. Mussels in the Mohammedia–Casablanca sector had the highest zinc concentrations (338–379 μg·g–1 dry weight), followed by those collected at Jorf Lasfar (267 μg·g–1 dry weight), and Sidi Moussa and Safi (290–301 μg·g–1 dry weight). The distribution of manganese concentrations, which were maximal in estuaries (up to 19 μg·g–1 dry weight), was indicative of terrigenous inputs. Seasonal variations in mussel metal concentrations were characterised by winter minima, and apparently related to the physiological cycle of the animal. With the exception of cadmium-contaminated areas, the quality of mussels on the Moroccan Atlantic coast is good with respect to food safety standards.

Changes in nekton community structure in north Brazilian intertidal mangrove creeks were studied by setting block nets at high water in the wet season 1999. From a total of 47 species (27 families), the most abundant were: Cathorops sp. (Ariidae), Colomesus psittacus (Tetraodontidae), Hexanematichthys herzbergii (Ariidae), Pseudauchenipterus nodosus (Auchenipteridae), the shrimp Fenneropenaeus subtilis (Penaeidae), Anchovia clupeoides (Engraulidae), Mugil spp. (Mugilidae), and Anableps anableps (Anablepidae). Diversity H' was low (0.9). Mean values of fish density and biomass (± S.E.) were 0.2 ± 0.1 fish m-3 and 2.6 ± 0.7 g m−3 or 1.4 ± 0.4 g m−2, respectively. The high proportion of juvenile fish (87%) and shrimps point to the importance of intertidal mangrove creeks for fish nurseries. The number of species was highest at spring tide-night and lowest at neap tide-day. Evenness J' was lowest at spring tide-night when more rare species entered and dominant species increased in quantitative proportions. Four different species assemblages were identified as being triggered by factor combinations such as “tide” and “time of day”: spring tide-night, spring tide-day, neap tide-night and neap tide-day. High-water level influenced the species assemblages, but salinity and water temperature did not. Abundance of 14 species correlated positively with the high-water level. Strong spring tides yielded extraordinary high nekton catches, suggesting that high-water level is an important parameter in the tidal migration of fish. Most fish entered the mangrove to feed. Predation pressure was considered to be low because of the presence of only a few, mainly juvenile predators. Beach seining in the subtidal parts at low water revealed a high biomass (30 ± 14 g m−2). Larger fish withdraw to depressions, small fish and juvenile shrimp were abundant near the shallow banks, suggesting inter- and intraspecific splitting of the migration routes when returning from the intertidal zone at ebb tide. To cover the entire short-term range of tidal ichthyofauna responses, a sample design should consider the spring/neap and the day/night cycle.

Catch-per-unit effort (CPUE) has frequently been used as an index of abundance and more specifically to calibrate virtual population analysis (VPA). In multi-species fisheries, CPUE calculated from fishing trips targeting the species seems to be more effective for calibration than the classical ratio total landings/total effort. Target species are determined from an analysis of the composition of catches (landings) of each fishing trip, each trip being categorised as to whether it targets the given species or not. It is obvious that existing but not reported discards would affect these results. Classification of trips can be achieved on a single-species basis, each species being considered successively and each trip possibly being relevant for more than one species. Using a more general approach, classification can be achieved by métiers, each of these being determined by one or a group of target species and each trip being categorised into one and only one métier. This method of categorising trips is based on thresholds of target species contribution to the catch and on an overall explanatory level. For the main species of the French demersal fishery off the west coast of Scotland and in the Celtic Sea, CPUEs are calculated using different methods to define the trips used to calculate fishing effort and associated landings. Besides important differences in actual values, CPUEs may also differ in their trends depending on the definition of directed effort. Tuned VPA, carried out for some species, shows that large variations in population estimates, fishing mortality or short-term predictions could occur when using directed effort, while the catchability model fits the data better.

The West-African neighbouring Gambia and Saloum estuaries function in different ways, the first being normal (saltier waters in the lower river, salinity range 0-38) and the second being inverse (saltier waters in the upper river, salinity range 36-90). The common cichlid species Sarotherodon melanotheron was collected in both systems over 16 months (June 2001 to September 2002) at five locations. We quantified reproductive traits from macroscopic examination of the gonads, oocyte counts and measurements, and growth from interpretation and measurements of an otolith sub-sample. There was a clear seasonal cycle of reproduction in the estuaries with a peak at the beginning of the wet season (May-July). Size at maturation was smaller in the more saline environment, the Saloum, for both females (170 mm in Gambia and 131 mm in Saloum) and males (162 and 113 mm respectively). The relative fecundity was lower and the oocyte size was bigger in the freshwater location of the Gambia river. Growth, estimated by counting the annual opaque zones on whole otoliths, was reduced in the hypersaline environment of the Saloum (L∞ = 198 mm, K = 0.26). Differences are less obvious between the growth in the Gambia (L∞ = 238 mm, K = 0.21) and that in the Saloum with a salinity of less than 60 (L∞ = 244 mm, K = 0.22). All these observations suggest that S. melanotheron is able to withstand saltier environments by limiting its growth, reducing the size-at-maturity, and changing its fecundity, but the most profound changes are only visible in hypersaline conditions.

Activity of digestive enzymes (trypsin, chymotrypsin and amylase) was studied in relation with food in Penaeus vannamei larvae first stages. Microparticles containing casein involved the decrease of soluble protein content and enzyme activities. Specific trypsin activity but not chymotrypsin was correlated (p < 1%) to casein level between 10 and 60% in microparticles. Cellulose fibres in food seemed to have little effect on digestive enzymes. Starch, between 1 and 20% in microparticles, had no influence on specific amylase activity. The effect of different feeding conditions were also tested on growth. No clear relationship between growth and enzyme is established since only trypsin is concerned in the case of a casein dose effect in the food. The protein source (casein, gelatin, squid meal or fish protein soluble concentrate) as well as the carbohydrate quality (soluble starch, standard corn starch, amylopectin corn starch or pregelatinized corn starch) were tested. Squid meal stimulated significantly chymotrypsinactivity (p < 2%) while trypsin activity decreased with fish protein soluble concentrate p < 5%). Source of carbohydrate seemed very important, amylase activity increased significantly ( p < 2%) with corn starch. These adaptations are not correlated to growth performances since squid meal or fish protein soluble concentrate improved larval development until zoe 3 substage. These results suggest a specific induction of digestive enzymes to the food quality in larvae independent of growth performances.

Fish catches around the Great Lake, Tonle Sap river and the transitional zone between the lake and the river were studied by professional ‘fishing lot' (i.e. fishing zone) from 1995 to 1997. One hundred and twenty species of fish, belonging to 26 families and nine different orders were recorded. Compared to previous studies (1936–1976), only 53 % of families, 32 % of genera and 54 % of species were collected by professional fishing lot. This important loss in biodiversity could have several causes: bias of sampling procedures between professional fishing and research sampling, overfishing, modification of the floodplain by deforestation, etc. The professional fishing data showed that Cypriniformes accounted for 41.6 % of the total number of individuals caught, the Cyprinidae family alone represented 40 species. Siluriformes made up 21.6 %, Perciformes 13.3 %, with six other orders represented by smaller numbers. Eighty-seven percent of the recorded species occur in both habitats depending on the season. Migration takes place from the Mekong river to the Great Lake through the Tonle Sap river at the beginning of the rainy season (May–October), and in the reverse direction at the start of the dry season (November–February). The majority of the species reproduce at the start of the rainy season (May–June) in the flooded plain and the forest floodplain of the Great Lake; the period, the place and the means of reproduction have not been closely studied, particularly for the Belontiformes, Clupeiformes, Synbranchiformes, Pleuronectiformes and Tetraodontiformes. Multivariate analysis of fishing data (November–February) shows three distinct communities: that of the lake (Perciformes and Siluriformes), of the river (Pleuronectiformes, Cypriniformes, Clupeiformes and Siluriformes), and of the transitional zone formed from the principal channel, the old river channel and the oxbow lakes (Cypriniformes, Siluriformes and Osteoglossiformes).

In Hawaii, a variety of small- and medium-scale pelagic fisheries target fishing effort on a network of coastal moored FADs, natural inshore tuna aggregation points, offshore seamounts and offshore weather monitoring buoys. Large-scale longline vessels also operate in the Hawaii exclusive economic zone (EEZ) and beyond. These circumstances provide an ideal setting for tag-and-release experiments designed to elucidate the movement patterns, residence times, exchange rates and vulnerability of bigeye tuna (Thunnus obesus) and yellowfin tuna (Thunnus albacares) within the Hawaiian EEZ. Preliminary recapture data indicate that FADs, island reef ledges and seamounts exert an overwhelming influence on the catchability of tuna. Recapture rates from these locations vastly outweigh tag returns from open water areas. As of August 31, 1999, a total of l5387 bigeye and, yellowfin tuna ranging in size from 29 to 133 cm fork length (FL) and from 26 to143 cm FL respectively (mean 59.8 ± 14.1 cm; 58.4 ± 17.3 cm) have been tagged and released throughout the Hawaii EEZ. Recapture rates for both species have been similar with an overall recapture rate of l0.3 %. The location of tag releases reflects the importance of associative behavior and schooling to the vulnerability of tuna; seamounts and FADs accounted for 72.4 % and 23.5 % of all tag releases. Within the main Hawaiian Island group (excluding the offshore seamounts and buoys), 83.1 % of all recaptures have been made on anchored FADs and 11.9 % of recaptures have come from ledges or tuna aggregation areas close to the islands where bigeye and yellowfin tuna become vulnerable to hook and line gear. As these studies continue, additional and longer-term recaptures will provide increasingly detailed information on the movement patterns and vulnerability of bigeye and yellowfin tuna as they grow, move and recruit to different fisheries.

Evaluating the ecological impact of an oil spill is a complex issue requiring coherently articulated examination of the sequence of interactions that link the cell, where contaminants exert their effects, to the ecosystem, where interactions with human activities arise. This sequence of interactions traverses the frontiers between scientific disciplines (chemistry, toxicology, physiology, and fisheries ecology). Using the common sole (Solea solea L.) as a model species for the coastal habitats polluted by the “Erika” oil spill, our research project attempted to define indices of functional integrity that characterised the consequences of fuel exposure at the different biological levels. The coupling of field observations with experimental laboratory work revealed how functional alterations which are readily observable within individuals and their organs are progressively obscured as investigation progresses towards more complex organisational levels. Some of the approaches and indices are proposed as instruments for evaluating the impact of contamination by hydrocarbons.