In the late 1980's juvenile oysters, Crassostrea virginica, spawned and cultured in New England and New York, began experiencing up to nearly 100% mortalities in some batches of juveniles. The cause of these mortalities was not ascertained immediately, but examination of dead and dying oysters did not reveal a previously recognized disease syndrome. Early studies showed that it was not an environmental or genetic problem, thus we hypothesized that a new, transmissible disease agent caused the observed mortality. This was verified under laboratory conditions where the disease was readily transmissible. Transmission was enhanced by warm water temperatures, 22–26 °C, and salinities of 18–30 ppt. Also, the infectious agent was filterable and sensitive to erythromycin, supporting the hypothesis that the causative agent may be a protistan parasite in the 2–6 μm size range. No evidence to support a viral or bacterial etiology was found.

We report the isolation, development and multiplex optimisation of 12 new microsatelliteloci for the great scallop, Pecten maximus. Diversity was moderate tohigh, with number of alleles ranging from 4 to 20 and observed heterozygosity between 0.28and 0.88. Progeny produced in a commercial hatchery was used to test locus power forparentage assignment. The percentage of offspring that was unambiguously assigned to aunique pair of parents was 97% (software package CERVUS-COLONY). Parentage assignmentrevealed that 22% of the studied progeny resulted from unplanned crosses. Effectivepopulation size of the study progeny was also estimated. Our study illustrates the powerof microsatellites for the genetic monitoring of hatchery-produced great scallops.

Over the past decades, pollution, overfishing, and habitat degradation have driven the population size of Taiwan shoveljaw carp down markedly in Taiwan. Cryopreservation is a useful tool which could be used to maintain genetic resources to protect and preserve this endemic species. Four cryoprotectants [dimethyl sulphoxide (DMSO), dimethylacetamide (DMA), glycerol and methanol] and six freezing rates (0.5, 1, 2, 4, 8, 16 °C min-1) were tested in order to develop an optimal controlled slow-freezing protocol for Taiwan shoveljaw carp spermatozoa. Samples were subsequently examined under the scanning electron microscope to reveal whether cryopreservation had affected their ultrastructural morphology. The highest survival rate (50.1 ± 2.0%) was observed with a freezing rate of 8 °C min-1 in 1M DMSO, using SYBR-14 + PI staining. Fertility and hatching rate results using frozen-thawed spermatozoa (90.2 ± 2.2% and 22.3 ± 2.5%, respectively) were not significantly different from results with fresh spermatozoa. After cryopreservation, 21.0 ± 1.6% of frozen-thawed spermatozoa had mid-piece swelling and rupture of the head. Cryopreservation might, therefore, slightly affect Taiwan shoveljaw carp spermatozoa in terms of morphological change. However, these alterations could be compensated by using large enough numbers of normally functioning frozen-thawed spermatozoa to achieve a standard equal to fresh spermatozoa. This is the first report of successful cryopreservation of Taiwan shoveljaw carp spermatozoa using a controlled slow-cooling method.

Heat shocks effective for the production of triploid brown trout (Salmo trutta) were optimized: 28 °C shocks lasting 10 to 15 minutes and applied 5 minutes after fertilization induce very high rates of triploidy (close to 100%) without causing much mortality; they can therefore be proposed for mass production of triploid brown trout. Female homogamety in that species is also demonstrated from analysis of gynogenetic progenies and progenies of sex-inverted females. Although the efficiency of masculinizing hormonal treatments requires further improvement, production of all-female sterile populations is now possible in this species promising for European sea-farming.

Two rainbow trout strains differing in their growth performance were used to study possible interactions between genotype, dietary composition and feed level on their feed utilisation efficiency and voluntary feed intake. Two diets (35 and 45 % of crude protein) and two feeding levels (to satiation or at a restricted level of 2 % of body weight), were used. The two diets were distributed, in duplicate, for each strain, during a four month growth trial. At the end of the experiment the digestibility of the two diets was determined in each strain, using chromic oxide, as a marker, and an automatic system for the faecal collection. The body composition of both strains was also analysed. The final weight of fish of the fast growing strain, fed to satiation, was significantly higher than that observed for fish of the slow growing strain. No significant differences were found between the strains's body weights, when a dietary restriction was made. Results observed for the feed-gain ratio were also similar between the two strains. The apparent digestibility coefficient (ADC) of dry matter and energy were significantly different between the two diets but similar for both strains. Concerning protein digestibility no significant differences were observed for diets, although one of the strains appeared to show a higher ADC for protein. Body composition as well as nitrogen and energy retention were similar for both diets and strains.

The capability of turbots to use self-feeders was studied using 3 groups of 100 juveniles. Feeding activity reached a plateau after 20 days. Almost all feeding activity was observed during the photophase, and the acrophase was associated with dawn. The proportion of nocturnal demands was the highest in the replicate with the lowest feed efficiency, suggesting that feed waste was mainly occurring during nocturnal feeding activity. During the last 30 days of the experiment, demands were only rewarded during two periods of 2.5 h.day−1. Feed efficiency was improved and was homogeneous between the three tanks, but the voluntary feed intake was reduced. It is concluded that turbots are able to use self-feeders but they do not adapt quickly, and they are not able to compensate a reduction of feed access by increasing demand activity during the access period.

The characteristics of the phytoplankton of Takapoto Atoll are reviewed from the studies conducted between 1974 and 1998. These studies mainly concerned the biomass and primary production of phytoplankton while the taxonomic composition received far less attention. The mean biomass is 0.2–0.3 μg chl a·L–1. The phytoplankton is homogeneously distributed on a year scale although an higher biomass (0.8 μg chl a·L–1) may temporarily exist in the south part of the atoll under moderate tradewinds or calm weather. The gross primary production reached 0.8 g C·m–2·day–1 whereas the net primary production is estimated to be 0.7 g C·m–2·day–1. No significant long-term changes of the biomass or primary production can be observed. The implications of this stability are discussed in the context of the mother-of-pearl mariculture. Size fractionated samples revealed the predominance of picophytoplankton which represented more than 60% of the phytoplankton biomass and achieved > 50% of the primary production. The taxonomic composition observed in 1974 showed the predominance of three algal groups: diatoms, dinoflagellates and coccolithophorids. The diatoms were the most diversified group, while the dinoflagellates were the most abundant. No further examination of the phytoplankton was undertaken until 1996. At that time, the microplankton was quite absent, and the phytoplankton communities were dominated by the pico- and nanophytoplankton, mainly chlorophytes, prymnesiophytes and dinoflagellates. This drastic shift of the phytoplankton communities towards smaller size is not clearly understood. It emphasises the need of taxonomic studies for a better understanding of the lagoon ecology.

Batch fecundity and relative fecundity of swordfish (Xiphias gladius) in the southwestern Indian Ocean were estimated from seven gravid swordfish females (size range 127–225 cm lower jaw-to-fork length, LJFL) with unovulated, hydrated oocytes collected onboard Reunion-based (France) longline swordfish fishing vessels between December 1999 to January 2001. To investigate the spawning pattern of swordfish, we used data collected through a combination of two at sea sampling regimes. A total of 17 007 geo-located size data of swordfish were recorded during 8 years (1993-2001) and a total of 1727 (size range 75–289 cm, LJFL) swordfish gonads (1107 females and 620 males) were sampled from May 1998 to January 2001. The estimated batch fecundity ranged from 995 000 hydrated oocytes for the smallest ripe female to 4.3 millions for the largest female sampled measuring respectively 127 to 225 cm in curved length (LJFL). The relative fecundity ranged from 25 to 72 hydrated oocytes per gram of body weight. We found that batch fecundity was positively correlated with fish length and that the older/larger females have earlier and longer spawning seasons than younger/ smaller females. These findings suggested that older/larger females which are seasonally migrating in this spawning ground seem to play a major role in reproductive success of the species in producing significantly more offspring than younger females during an extended spawning season. Examination of the length-frequency date from the fishery indicated that the young fish are resident around Reunion and around the seamounts off Reunion Island. Our results highlight the important role of the older/larger females in the reproductive capacity of southwestern Indian Ocean stock. We discuss the potential implications of fishing the older/larger females for this stock in terms of reproduction and recruitment.

Murine monoclonal and polyclonal antibodies to antigens of Bonamia ostreae were assessed for serological comparison of parasites associated with different geographical origins of flat oysters, Ostrea edulis, and with Tiostrea lutaria. All Bonamia isolates from O. edulis reacted similary with polyclonal and monoclonal antibodies. The parasite associated with Tiostrea lutaria which lacks reactivity with 20 B2 MAB must be considered as a serologically distinct form of B. ostreae.

Gonadal neoplasms (germinomas) in softshell clams, Mya arenaria, have only been reported from locations in Maine, USA despite the fact that the geographic range of M. arenaria extends from Labrador to North Carolina on the east coast of North America. To more accurately determine the geographic distribution of this disease, adult clams (n = 18–60 per sample) obtained between 1989 and 1997 from sites along the entire coast of Maine and from Atlantic Canada (New Brunswick, Nova Scotia, and Prince Edward Island) were examined histologically for the presence of neoplasia. Gonadal neoplasms were present at 10 of the 28 locations sampled, including sites in Maine, New Brunswick, Nova Scotia, and Prince Edward Island, at prevalences ranging from 3.3 to 50% and at all stages of development. Prevalence and stage of development, however, were consistently greater at sites located between Penobscot Bay, Maine and Passamaquoddy Bay, New Brunswick. There was no correlation between mean clam size (shell length) and prevalence. Clams with neoplasia were predominantly female. To assess possible disease transmissibility and subsequent mortality rates, naïve clams were transplanted to a site where neoplasia is enzootic and placed in close proximity to clams having the disease. After 6 months, no evidence of neoplasia was found in the transplanted clams even though cumulative mortality (14.7%) was greater than that in local clams (3.4%). These results suggest that gonadal neoplasms in M. arenaria progress slowly and cause little mortality once present in an individual and may not have an infectious etiology. Loss of reproductive output is a potential long-term effect of the disease.

The biochemical composition and biometry of different Artemia salina stages were determined in four ponds of increasing salinity (M1, M2, M3 and B1) in the Sfax solar saltern (Tunisia). Results showed the dominance of saturated fatty acids, which made up 48 to 57% of total fatty acids (FAs). Polyunsaturated fatty acids (PUFAs) 22:6(n-3) docosahexaenoic acid (DHA) and 20:5(n-3) eicosapentaenoic acid (EPA) represented on average only 3.1 and 4.0% of total FAs respectively. A. salina nauplii, cysts and metanauplii, in ponds M1, M2 and B1 respectively, were found to have optimal DHA/EPA ratios (>2) for use as live feed for invertebrate and fish larvae. Significant inter-pond variation in DHA/EPA levels was also recorded. The predominant FAs in Artemia were negatively correlated with both temperature and salinity. FA and protein contents were strongly affected by high temperatures (>30 °C) and probably by food sources (e.g., Dunaliella salina) (r = 0.9, n = 27). The density of Artemiasalina was positively correlated with protein content in pond B1. The high DHA/EPA ratios (1 to 3.3) found in this study indicate that Sfax Artemia could be a valuable food source for larvae in large marine hatcheries and also for some aquarium species.

Scanning electron microscopic observation of embryos and larvae of the carp (Cyprinus carpio) in the course of development was undertaken to further understanding of the relationship between larval behaviour and their chemo- and mechanoreceptors. Free neuromasts and olfactory pits equipped with mechano- and sensory-cilia were found on carp embryos. During larval development, the number of neuromasts and the olfactory mechano- and sensory cilia steadily increases and they become more morphologically differentiated. The olfactory features, presented in early larval stages, indicate that although the olfactory organ at this early life history has not yet attained its final configuration, it can perceive odour stimulation. The neuromasts found on the forehead of the newly hatched larvae seem to assist in the early behavioural selection, approach and attachment to a substratum, before the stage of filling of the gas bladder. The increasing number of neuromasts during development reflects the larvae's capability of capturing food items in the absence of visual stimulation. The rapid maturation of free neuromasts, the lateral-line system and the olfactory organ, is evidence of their post-metamorphosis position in the search for, location and successful capture of food.

Hydroacoustical estimation of fish abundance and distribution is performed in three reservoirs that are characterised by different levels of eutrophication. The Biosonics 101 dual beam echosounder with a frequency of 420 kHz and the ESP software for acoustical data analyses are used. A clear dependence between fish density and the level of eutrophication is observed. In the mesotrophic Solina reservoir, fish abundance is over an order of magnitude lower than that in the eutrophic Dobczyce and Sulejów reservoirs. Fish length distributions have different shapes in the three reservoirs, which indicates the changes in fish size structure due to eutrophication; however, the mean target strength of fish does not differ significantly. These results suggest that hydroacoustically collected data may help to assess the ecological state of inland waters and may be used together with other methods in monitoring the water quality.

Yellowfin and bigeye tunas (Thunnus albacores and Thunnus obesus) were tagged and released between August 1995 and December 1997 at Cross Seamount and NOAA weather buoys about 200 Nmi south of Honolulu. The release and recapture data were stratified into five sites, and a bulk transfer model was used to estimate natural mortality, fishing mortality and transfer rates between the five sites. Bigeye are much more persistent at Cross seamount and less vulnerable to the fishery than yellowfin. Fishing accounts for about 5 % of the total mortality of both bigeye and yellowfin at Cross Seamount. Yellowfin are a major component of catches at inshore FADs in Hawaii. The rate of immigration from Cross Seamount to the inshore FADs is very low for both species. The fishing mortality at Cross seamount is substantial but is not adversely impacting the populations either at Cross or the inshore FADs.

A hydroacoustic monitoring technique to quantify and assess the ecological requirements for migration of the anadromous clupeid, Alosa fallax fallax (twaite shad) was developed, and its effectiveness studied, on the River Wye in Wales. The acoustic monitoring technique was a side aspect application, with two transducers fixed permanently to the riverbank and the acoustic beam from each aimed horizontally across the river towards the opposite bank, perpendicular to flow. Two split-beam echo sounders and transducers were deployed, each operating at different frequencies (200 and 420 kHz). Using a combination of these two frequencies it was possible to demonstrate that shad show bold avoidance behaviour to sound transmitted at 200 kHz and would not pass the monitoring site when sound was transmitted at this frequency. They remained unaffected by sound transmitted at 420 kHz and were observed migrating upstream in large, loosely aggregated shoals. From visual observations above and below the water, shoals were estimated to comprise of many hundreds of individuals, covering a size range of between 30 and 45 cm. Only a few individuals could be resolved by the acoustic system operating at 420 kHz, and it was therefore, not possible to obtain a count of fish by "target tracking" single shad. However, by transmitting 200 kHz sound pulses on a 50% duty cycle the seasonal and daily patterns of shad migration were derived from the analysis of data gathered by the acoustic system operating at 420 kHz.

Farfantepenaeus notialis (Crustacea, Decapoda) constitutes about 70% of the total shrimp catch in the Colombian Caribbean. In this study, we examined morphological characteristics of F. notialis to investigate stock differentiation, provided biological data such as size at 50% sexual maturity and discussed the importance of this information to fisheries management. The study was conducted in the Colombian Caribbean Sea from June to December of 2004 in four locations: Uraba gulf, Morrosquillo gulf, Amansaguapos, and La Vela cape. Individual shrimp were measured according to ten body segments and sex determined. We used discriminant function analysis (DFA) of size-adjusted data to generate two-dimensional plots of the morphometric indices to test for geographic variation in morphometry by mean of canonical dimensions. The length-frequency distributions showed statistically significant differences between the measurements of both sexes, males were smaller than female in all measures. In females, size range was 16 to 46 mm cephalothorax length (CL) and size at sexual maturity (CL50%) was 30.6 mm. Size range was 19 to 32 mm (CL) for males. The DFA of morphological differences between individuals (female/male) showed strong overlapping and no clear separation between regions. We did not find morphometric variability between regions, which indicates a single population of F. notialis from the morphometric point of view.

Fish stocks found on lagoon bottoms and near reefs are characterized by a high diversity and heterogeneous habitat which make stock estimation difficult. In particular, it is necessary to combine several methods in order to evaluate the major components of these stocks. The present study aimed at estimating reef fish stocks in the Northern Province of New Caledonia, a region where they represent a major target for the local fishermen. These estimates were based on experimental fishing with handlines and bottom longlines. Handlines were used to assess the stocks near reefs, and longlines for those in areas away from reefs and on lagoon soft bottoms. Handline stations (363) were sampled in three different regions (west, north and east lagoons) and three biotopes (nearshore, middle lagoon and barrier reef). A total of 104 species were caught, the major families being Lethrinidae, Lutjanidae and Serranidae. Species composition and catch per unit of effort (CPUE) varied among regions and biotopes. In particular, the north zone showed characteristics of an unexploited area with very high yields. An increase in CPUE and fish size from the coast towards the barrier reef and with increasing depth was observed in all regions. Correlations between CPUE from handlines and the numerical density and biomass estimates from underwater visual censuses (UVC) performed on nearby reefs were significant. A total of 206 longline stations were sampled in the west and east regions. A total of 80 species were caught, the major families being the same as those caught in stations with handlines with the addition of Carangidae. The CPUE of longlines was significantly correlated with numerical density and biomass estimates made by UVC along the longlines. Stock estimates based on the correlations between CPUE from handlines or longlines and UVC estimates indicate that 90 % of the lagoon stock were found on soft bottoms and near reefs. Reefs, despite biomasses that were five times larger than soft-bottom and near-reef areas, made only a small contribution to total stock. The ratio between density and CPUE was highest for the lowest densities, thus indicating that fishing efficiency increased with density. Comparison of handline catch performed around reefs and UVC data from nearby reefs suggests that there were bold relationships between the fish assemblages of these two biotopes.

Monthly variations in spatial and depth distributions, sex ratios, and maturity status in two species of hakes, Merluccius hubbsi and M. australis, were analysed in an area where their ranges overlap spatially on the shelf and slope around the Falkland Islands, and in international waters at 45–47° S (High Seas), using data collected by scientific observers on commercial fishing vessels. A variety of exploratory analyses were carried out on the raw data before patterns were quantified using generalised additive models. Both species use the areas studied as their feeding grounds. M. australis occur mainly on the Falkland shelf south of 51° S, whereas M. hubbsi is widely distributed throughout both the Falkland and High Seas shelf areas. Preliminary schemes of the seasonal migrations of both hakes in Falkland waters and on the High Seas are suggested and discussed. M. hubbsi and M. australis are found to be boldly segregated, both spatially and temporally, on their common feeding grounds, thus avoiding potential inter-specific competition for food resources.

This paper describes the large-scale production of eggs and larvae of sea bass (Dicentrarchus labrax) and shows how spawning can be planned to produce viable eggs throughout the year by manipulation of photoperiod and temperature. The rearing temperature was 9.5-22 °C during spawning and 9-24 °C during the gametogenesis. The photoperiodic cycles tested were normal (i. e. the photoperiodic cycle observed at Palavas-les-Flots, mediterranean coast, France, 1984/1987) advanced by 3 to 5 months and delayed by 2 months.

To protect public health, the European Commission established maximum levels of certain contaminants permitted in foodstuffs. The maximum amount of lead allowed in bivalve mollusc is 1.5 µg g−1 wet weight. In the Galician Rías, which are important areas of shellfish production in Spain, high levels of lead have been detected in the commercial bivalve Dosinia exoleta (Veneridae). Given the environmental and socio-economical problems this could represent, Pb concentration was tested in D. exoleta from two Rías, and the relation of lead accumulation with body size studied in detail. Implications for fisheries management are also discussed in this paper. Results showed a strong dependence of Pb accumulation on body size, with lead concentrations increasing exponentially with shell length. Larger animals presented a 5-fold increase in lead concentrations above the maximum permitted level. The size limit (length beyond which D. exoleta should not be extracted for commercial purposes) was initially established at 40 mm; but a more comprehensive geographical study of Pb concentrations in individuals from 35 to 40 mm long revealed that this size limit was not protective enough, and 35 mm is proposed as a safer limit.