Vincent Buchet

Effect of lipid level in a compound diet on the development of red drum (Sciaenops ocellatus) larvae.

Red drum larvae were fed, from day 11 to day 24 post-hatch, with Artemia (LP group) or two isoproteinic-formulated diets with varying lipid levels, 15% (L15 group) and 30% (L30 group). The lipid fraction was composed of a mixture of cod liver oil and soy lecithin. Larvae fed Artemia exhibited the greatest length; L30 diet induced a larvae length significantly greater than that obtained with L15 diet (P<0.05). No difference was observed in larvae survival among the three dietary groups. The increase in dietary lipid concentration led to an increase in amylase and trypsin secretion levels in 24-day-old larvae. The pancreatic secretion level measured in L30 group was close to that of LP group, suggesting that the maturation of the pancreatic functions was normally developed. Red drum larvae fed the diet containing the higher lipid content (L30) exhibited a more developed brush border membrane digestion in the intestine than larvae fed L15 diet (P<0.05). Phospholipase A2 was stimulated by the increase of phospholipids in the diet, but no difference was observed for lipase between the two compound diet-fed groups; the LP group exhibited the lowest lipase activity. A plateau in lipase activity may have occurred in red drum larvae from 15% fat level in the diet, suggesting that the maximal lipase activity was reached with 12% neutral lipid in the diet. The positive effects observed with high dietary fat may be due to the phospholipid fraction of the lipid mixture used.

Relationship between PAH biotransformation as measured by biliary metabolites and EROD activity, and genotoxicity in juveniles of sole (Solea solea)

Polycylic aromatic hydrocarbons (PAHs) are ubiquitous contaminants in the marine environment. Their toxicity is mainly linked to the ability of marine species to biotransform them into reactive metabolites. PAHs are thus often detected at trace levels in animal tissues. For biomonitoring purposes, this findings have two main consequences, (i) the determination of the PAH tissue concentration is not suitable for the evaluation of individual exposure to PAHs (ii) it can explain sometimes the lack of correlations obtained with relevant markers of toxicity such as genotoxicity biomarkers. The aim of the present study was to better investigate the link between PAH exposure and genotoxicity in marine flatfish. During a laboratory experiment, juvenile soles were exposed for four weeks to a mixture of three PAHs, namely benzo[a]pyrene, fluoranthene and pyrene, followed by one week of depuration. Fish were exposed via the trophic route to a daily PAH concentration of 120 μg/g food. Fish were sampled at different time points. The bioavailability and the biotransformation of PAHs were assessed by the measurement of biliary metabolites using a sensitive UPLC MS/MS method. The 7-ethoxyresorufine-O-deethylase was also measured in liver subcellular fractions as a biomarker of phase I biotransformation activities. Genotoxicity was assessed in parallel by the measurement of DNA strand breaks in fish erythrocytes by the alkaline comet assay. During this study, the high amount of PAH metabolites produced in sole demonstrated the bioavailability of PAHs and their biotransformation by fish enzymes. A positive correlation was observed between the level of hydroxylated PAH metabolites and genotoxicity as measured by the alkaline comet assay.

Laboratory study on the effect of dichlorvos on two commercial bivalves

Organophosphorus compounds (metrifonate, dichlorvos) are commonly used in marine fish farms to control ectoparasitic copepods or monogeneans populations. After fish treatment, these products may be discharged directly in shellfish growing areas. As they are known for their environmental toxicity, it becomes necessary to study the effect of these chemicals on the bivalves. Two commercial bivalves: Manila clam, (Ruditapes philippinarum) and Japanese oyster (Crassostrea gigas) have been exposed for 6 h to 1 and 0.1 mg l−1 dichlorvos concentrations and then replaced in drug-free seawater until the end of the experiment (48 h). The behaviour and mortality of the shellfish have been observed. The specific acetylcholinesterase activity (AChE) was measured in the total clam tissue and the oyster gills following the automated method of Galgani and Bocquene (1988). No abnormal mortality was observed, but all bivalves were opened because of a relaxation of the adductor muscles. AChE inhibitions were 40 and 70% (for 0.1 and 1 mg l−1 dichlorvos concentrations respectively) for clams and 83 and 87% (for 0.1 and 1 mg l−1 dichlorvos concentrations respectively) for oysters. Forty-two hours after the end of the exposure, the AChE activity of oyster remained low and a partial recovery of the initial activity was observed for clams. These findings illustrated that the concentrations tested are not lethal but have a clear effect on the bivalves physiology. Therefore it may be considered that because of the dilution and degradation processes dichlorvos effect is only limited to bivalves reared within or in close contact with fish farms.

Preliminary study on the kinetics of oxytetracycline in shellfish exposed to an effluent of a land-based fish farm: Experimental approach

Abstract In many ancient saltmarshes marine fish farms are now being developed. These farms, during their production cycles, use many chemical and veterinary products to prevent or fight disease. Since effluents from the farms are discharged directly into shellfish rearing areas, it is necessary to be aware of how shellfish accumulate such substances. An experimental apparatus allowed the creation of a fish farm effluent containing oxytetracycline (OTC) for a seven day treatment period. This effluent was poured into three test tanks, into which individuals of three edible species of bivalves, Crassostrea gigas, Ruditapes philippinarum and Scrobicularia plana , had previously been placed. The highest concentrations were observed in C. gigas (average 1.42 μg.g −1 wet weight). After treatment, the OTC concentration decrease was gradual and slow in C. gigas , reaching 0.68 μg.g −1 wet weight 14 d after the end of medication. Concentrations were stable in R. philippinarum and S. plana until the end of the experiment. Differences observed in the kinetics and maximal OTC concentration values may be related to the filtering rate of the species and their feeding behaviour. These findings illustrated the long persistence of OTC in shellfish. This may be related to the availability of OTC from sediment, the formation of complexes between OTC and some mineral or organic components of the bivalves, and their low xenobiotic metabolism. Considering the dilution processes of the coastal ecosystem, one might surmise that the influence of such contamination is only restricted to the vicinity of the farms. Nevertheless, special care should be taken in the utilization of such substances, especially in integrated aquaculture systems.

Comparative Allometric Growth of the Mimetic Ephippid Reef Fishes Chaetodipterus faber and Platax orbicularis.

Mimesis is a relatively widespread phenomenon among reef fish, but the ontogenetic processes relevant for mimetic associations in fish are still poorly understood. In the present study, the allometric growth of two allopatric leaf-mimetic species of ephippid fishes, Chaetodipterus faber from the Atlantic and Platax orbicularis from the Indo-Pacific, was analyzed using ten morphological variables. The development of fins was considered owing to the importance of these structures for mimetic behaviors during early life stages. Despite the anatomical and behavioral similarities in both juvenile and adult stages, C. faber and P. orbicularis showed distinct patterns of growth. The overall shape of C. faber transforms from a rounded-shape in mimetic juveniles to a lengthened profile in adults, while in P. orbicularis, juveniles present an oblong profile including dorsal and anal fins, with relative fin size diminishing while the overall profile grows rounder in adults. Although the two species are closely-related, the present results suggest that growth patterns in C. faber and P. orbicularis are different, and are probably independent events in ephippids that have resulted from similar selective processes.

Infectivity and RNA persistence of a norovirus surrogate, the Tulane virus, in oysters.

Oysters, being filter feeders, can accumulate some human pathogens such as norovirus, a highly infectious calicivirus, most common cause of acute gastroenteritis worldwide. Accumulated virus decays over a period of days to weeks, possibly rendering contaminated oysters safe again. Sensitive molecular methods have been set up for shellfish analysis but without answering the question of infectious virus detection. Using the Tulane virus (TV), a norovirus surrogate that recognizes the same ligand as human norovirus in oyster tissues, the genome and infectious virus decay rates were estimated using inverse linear regression in a Bayesian framework for genome copies. Infectivity decreased faster than genome copies but infectious viruses were detected for several days. Quantifying the decrease in viral infectivity and genome detection in oysters over such a long period may help local authorities to manage production areas implicated in shellfish-borne outbreaks, and thus protect consumers.