Spatio‐temporal trends of sailfish,Istiophorus platypterus catch rates in relation to spawning ground and environmental factors in the equatorial and southwestern Atlantic Ocean

Spatial and temporal trends of sailfish catch rates in the southwestern and equatorial Atlantic Ocean in relation to environmental variables were investigated using generalized additive models and fishery‐dependent data. Two generalized additive models were fit: (i) ‘spatio‐temporal’, including only latitude, longitude, month, and year; and (ii) ‘oceanographic’, including sea surface temperature (SST), chlorophyll‐a concentration, wind velocity, bottom depth, and depth of mixed layer and year. The spatio‐temporal model explained more (average ~40%) of the variability in catch rates than the oceanographic model (average ~30%). Modeled catch rate predictions showed that sailfish tend to aggregate off the southeast coast of Brazil during the peak of the spawning season (November to February). Sailfish also seem to aggregate for feeding in two different areas, one located in the mid‐west Atlantic to the south of ~15°S and another area off the north coast of Brazil. The oceanographic model revealed that wind velocity and chlorophyll‐a concentration were the most important variables describing catch rate variability. The results presented herein may help to understand sailfish movements in the Atlantic Ocean and the relationship of these movements with environmental effects.     

Recirculation nursery systems for bivalves

In order to increase production of bivalves in hatcheries and nurseries, the development of new technology and its integration into commercial bivalve hatcheries is important. Recirculation aquaculture systems (RASs) have several advantages: high densities of the species can be cultured resulting in a cost-effective production system; optimal temperature maximizes production and allows rapid turnover of the product; stable water quality improves growth rate and minimizes stress and potential loss by diseases. Pilot RAS systems were developed for seed rearing of oysters (Crassostrea gigas), scallops (Pecten maximus), mussels (Mytilus edulis) and clams (Ruditapes decussatus). Optimal feed addition and waste matrix were determined. Based on this, system flow rates were designed. Seed growth in the pilot RAS systems was compared at different renewal rates and with growth in flow-through systems (FTS). All four species can be reared in RAS and showed similar growth in RAS and in FTS or in RAS with a higher renewal rate. RAS can keep O₂, nitrogen and pH within the desired range. Temperature was generally higher in RAS than in FTS, probably due to heat induced by the pump circulating the water. The supply of sufficient amount of food in combination with a desire to reduce the renewal rate calls for use of concentrated feed in RAS.     

Production of meiotic gynogenetic and triploid sea bass, Dicentrarchus labrax L.: 1. Performances, maturation and carcass quality

Meiotic gynogenetic and triploid sea bass were produced by pressure shocks according to a previously published protocol. Pressure-treated groups did not survive as well as controls during early development and larval rearing. Performances, sexual maturation and carcass quality were examined over a period of 34–45 months. At the age of 34 months, growth of the gynogenetic fish was comparable to that of the control but inferior in the triploid fish. A predominance of male fish was found within the triploid groups, while diploid and meiotic gynogenetic fish showed equal proportions of the sexes. Gonadal maturation in triploid fish was significantly impaired, particularly in the females that showed rudimentary ovaries. Triploid males exhibited primary maturation but proved to be gametically sterile. Pressure-induced triploids did not grow as well as diploids, but these results might be ascribed to specific on-growing conditions (communal rearing). The performance of gynogenetic sea bass was comparable to that of control. The superiority of diploid fish over their triploid counterparts was confirmed during the final growing period and more clearly so in females. Performances of triploids varied according to their maternal origin. Overall, striking qualitative differences between diploid and triploid fish were found at the age of 34 and 45 months, although the results varied in a gender-specific manner. A strong maternal effect was also observed. The potential advantages of triploid sea bass for aquaculture purposes are discussed.     

Occurrence and present status of coastal dolphins (Delphinus delphis and Tursiops truncatus) in the eastern Ionian Sea

• 1. Boat surveys aimed at studying short‐beaked common dolphins and common bottlenose dolphins in eastern Ionian Sea coastal waters were conducted between 1993 and 2003. During 835 survey days, 24 771 km of total effort was distributed within an area of 480 km², resulting in 428 common dolphin and 235 bottlenose dolphin sightings.
• 2. Individual photo‐identification was performed extensively throughout this study, making it possible to monitor the number of animals seen in the study area each year and their long‐term residency patterns.
• 3. Common dolphins declined across the study period, from 2.18 encounters/100 km in 1997 to 0.40 encounters/100 km in 2003. In contrast, there was a relatively stable presence of bottlenose dolphins, some individuals showing high levels of site fidelity and others using the area only occasionally.
• 4. The local decline of common dolphins and the low density of bottlenose dolphins appeared to reflect the general status of these cetacean species in the wider Mediterranean region, where common dolphins were classified as endangered in the IUCN Red List in 2003.
• 5. Based on the available evidence, we infer that the present unfavourable status of common dolphins in eastern Ionian Sea coastal waters is largely a consequence of prey depletion.

Copyright © 2005 John Wiley & Sons, Ltd.     

Feed or food responsible for the presence of low-level thiouracil in urine of livestock and humans?

In recent years, questions have been raised on the possible semi-endogenous status of the alleged xenobiotic thyreostatic drug thiouracil; thiouracil has been detected in the urine of various animals (livestock and domesticated) at concentrations between 1 and 10 μg L(-1) and also in human urine. Although several studies suggest Brassicaceae-derived feed as potential origin, no traces of thiouracil have been detected in feed so far. Therefore, the aim of this study was to elucidate the origin of thiouracil in the urine of livestock and humans. To this purpose various Brassicaceae feed and food sources (e.g., rapeseed, rapeseed coarse meal, cabbage, cauliflower, broccoli) were investigated for the presence of thiouracil. In addition, the impact of the Brassicaceae-related β-thioglucosidase enzyme was evaluated. This myrosinase enzyme appeared to be crucial, because without its catalyzed hydrolysis no thiouracil could be detected in the various Brassicaceae-derived samples. Therefore, a sample pretreatment with incorporated enzymatic hydrolysis was developed after ensuring the quality performance of the extracted myrosinase mixture with a single-point glucose assay. Upon enzymatic hydrolysis and LC-MS(2) analysis, thiouracil was successfully detected in samples of traditional rapeseed, rapeseed-'00' variety coarse meal (values of erucic acid <2% and glucosinolates <25 μmol g(-1)), and rapeseed cake at 1.5, 1.6, and 0.4 μg kg(-1), respectively. As for the food samples, broccoli and cauliflower displayed thiouracil concentrations of 6.0 and <1.0 μg kg(-1), respectively. To the best of the authors' knowledge this study is the first to report the presence of naturally occurring thiouracil in feed and food samples. Future research should investigate the pathway of thiouracil formation and identify its possible precursors.     

Summer mortality of hatchery-produced Pacific oyster spat (Crassostrea gigas). I. Estimation of genetic parameters for survival and growth

The multidisciplinary project “MOREST” aims to improve our understanding of causes of summer mortality in Crassostrea gigas juveniles in France and to reduce its impact on oyster production. As part of the MOREST project, 43 full-sib families nested within 17 half-sib families were produced, planted out and tested in 3 sites during summer 2001 to assess to what extent genetic variability exists for this trait. A strong genetic basis was found for survival as narrow-sense heritability estimates ranged from 0.47 to 1.08, with higher values in sites where summer mortality was higher. Genetic correlations across sites were positive and very high for survival, indicating no genotype by environment interaction. In contrast, lower genetic variation was observed for growth in all sites. Finally, genetic correlations between growth and survival were low, in all sites. Selective breeding in a single site should therefore be an efficient means of improving survival in oysters less than one year old along the French Atlantic and Channel coastlines with only very limited effects on growth. As yield mostly depends on survival and growth, this approach should significantly improve harvestable yield. Possible reasons why a high genetic variance for survival appears to be maintained in wild populations are discussed.     

Natural abundance of 18O of sugar biomarkers in topsoils along a climate transect over the Central Scandinavian Mountains,Norway

Precipitation and topsoil samples from a climate transect over the Scandinavian Mountains, Norway, were analyzed for bulk and compound‐specific δ¹⁸O values. The natural abundance of ¹⁸O in the plant‐derived hemicellulose biomarkers arabinose and xylose correlates positively with δ¹⁸O of bulk soil, but not with δ¹⁸O of precipitation. This suggests that other factors than δ¹⁸O_prec, such as evaporative ¹⁸O enrichment of leaf water, exert a strong influence on the natural abundance of ¹⁸O in soils.     

Limnology of Macrobrachium amazonicum grow‐out ponds subject to high inflow of nutrient‐rich water and different stocking and harvest management

We evaluated the water characteristics and particle sedimentation in Macrobrachium amazonicum (Heller 1862) grow‐out ponds supplied with a high inflow of nutrient‐rich water. Prawns were subject to different stocking and harvesting strategies: upper‐graded juveniles, lower‐graded juveniles, non‐graded juveniles+selective harvesting and traditional farming (non‐grading juveniles and total harvest only). Dissolved oxygen, afternoon N‐ammonia and N‐nitrate and soluble orthophosphate were lower in the ponds in comparison with inflow water through the rearing cycle. Ponds stocked with the upper population fraction of graded prawns showed higher turbidity, total suspended solids and total Kjeldahl nitrogen than the remaining treatments. An increase in the chemical oxygen demand:biochemical oxygen demand ratio from inlet (4.9) to pond (7.1–8.0) waters indicated a non‐readily biodegradable fraction enhancement in ponds. The sedimentation mean rate ranged from 0.08 to 0.16 mm day^?1 and sediment contained >80% of organic matter. The major factors affecting pond ecosystem dynamic were the organic load (due to primary production and feed addition) and bioturbation caused by stocking larger animals. Data suggest that M. amazonicum grow‐out in ponds subjected to a high inflow of nutrient‐rich water produce changes in the water properties, huge accumulation of organic sediment at the pond bottom and non‐readily biodegradable material in the water column. However, the water quality remains suitable for aquaculture purposes. Therefore, nutrient‐rich waters, when available, may represent a source of unpaid nutrients, which may be incorporated into economically valued biomass if managed properly.     

Purification of chinook salmon (Oncorhynchus tshawytscha) GH for receptor study

A method for the purification of chinook Salmon (Oncorhynchus tshawytscha) GH, which retains its biological activity, is described. The biological activity was investigated with an established radioreceptor assay using liver membranes from pregnant rabbits and bovine GH as standard and labelled hormone. The enrichment of the preparation was checked with electrophoresis (SDS-PAGE). Extraction and further steps were carried out using low molarity alkaline buffer (pH 8–10, M = 100 mM). Three chromatography steps were performed (Concanavalin-A sepharose, Bio-gel P60, DEAE). Ion exchange chromatography was performed under isocratic conditions (using a 50 cm column). Two isoforms (sGH1 and sGH2) were isolated. The purification yield is 0.7% compared to lyophilized pituitaries. The molecule is homogeneous in SDS-PAGE. Contamination by prolactin, gonadotrophin and corticotrophin is negligible (< 0.5%). It could be demonstrated that the biological activity of the preparation is maintained since this preparation stimulates the growth of juvenile trout (Salmo gairdneri) and binds specifically (35%) to trout liver membranes.