Lewis Le Vay

Biochemical composition and digestive enzyme activity in larvae and postlarvae ofPenaeus japonicus during herbivorous and carnivorous feeding

The growth, survival, digestive enzyme activity and biochemical composition ofPenaeus japonicus (Bate) larvae and postlarvae were measured under three feeding regimes. Larvae were reared through the protozoeal stages usingChaetoceros gracilis. From the first mysis stage, three feeding regimes were used; (A)C. gracilis plusArtemia sp. nauplii, (B)Artemia sp. nauplii alone or (C)C. gracilis alone. No significant difference was found in growth, survival, protein content or lipid content of postlarvae from the treatments receiving the single-feed type, despite the low protein (7%) and highly unsaturated fatty acid content of the alga. Growth of larvae receiving the mixed diet was significantly higher than in the other treatments. Trypsin activity was more strongly influenced than amylase activity by dietary treatment, and differences in the ratio of these enzymes between treatments suggest independent control of their secretion. Trypsin activity recorded in larvae feeding onC. gracilis was up to six time higher than in larvae feeding onArtemia sp. nauplii, apparently in response to the low protein content of the alga. Larvae receiving the mixed diet exhibited an intermediate level of trypsin activity; it is suggested that the ingestion of algae is necessary for optimal assimilation of the zooplankton component of the diet.

The digestive physiology of herbivorous, omnivorous and carnivorous crustacean larvae: a review

Abstract While most copepods are holoplanktonic, decapod larvae are meroplanktonic with a pelagic larval development ranging from days (Penaeidae) to weeks (most Palaemonidae, Palinuridae). Reproductive strategies result in either the early release of larvae in large numbers of small planktonic forms (Penaeidae) or smaller numbers of advanced larvae after parental incubation (Brachyura, Palaemonidae, Nephropidae, Palinuridae). Commercially-cultured decapod larvae exhibit a wide range of feeding strategies exploiting most of the trophic levels found within the planktonic ecosystem. Studies on these crustacean larvae demonstrate how their digestive physiology is adapted to different feeding strategies during larval development, and provide an insight into the design of appropriate artificial feeds for commercial culture. Comparative measurements of digestive enzyme levels reveal that trypsin-like protease appears to dominate in all larvae investigated. Highest levels occur in herbivorous penaeid and brachyuran larval stages. In contrast, carnivorous lobster and caridean larvae show low protease activity at first feeding and appear to rely upon high-energy digestible live prey for their nutrition. Ontogenetic changes in enzyme type, activity and content are displayed during the penaeid mysis and caridean, brachyuran late zoeal stages as larvae transfer to higher trophic levels. The range and extent of these changes are reviewed for the commercial larval groups of commercially important species.

Are mangroves worth replanting? The direct economic benefits of a community-based reforestation project

SUMMARY Competition for coastal land use and overexploitation have reduced or degraded mangrove coverage throughout much of their distribution, especially in South-east Asia. Timber production was the initial motivation for early mangrove reforestation projects. Morerecently,benefitsfromprotectionagainsterosion and extreme weather events and direct improvements in livelihoods and food security are perceived as justifications for such restoration efforts. This study examines the socioeconomic impacts of a communityled reforestation project in the Philippines through a survey of the local fishers. Revenues from mangrove fisheries,tourismandtimberresultinanannualbenefit to the community of US

Digestion in relation to feeding strategies exhibited by crustacean larvae.

315ha −1 yr −1 .T his fi gure is likelytobeconsiderablymoreifthecontributionofthe mangrove to the coastal catch of mangrove-associated species is included. This estimate only includes direct benefits to the community from mangroves, and not intangible benefits such as coastal protection, which paradoxically is perceived by the community as one of the most important functions. More than 90% of all fishers, regardless of where they fished, thought the mangrove provided protection from storms and typhoons and acted as a nursery site and should be protected. Those fishing only in the mangrove perceived more benefits from the mangrove and were prepared to pay more to protect it than those fishing outside. This study concludes that replanting mangroves can have a significant economic impact on the lives of coastal communities. Acknowledgement of the value ofreplanted mangroves compared with other coastal activities and the benefits they bring to the more economically-vulnerable coastal dwellers should support better informed policy and decision-making with regard to coastal habitat restoration.

Influence of live and artificial diets on tissue composition and trypsin activity in Penaeus japonicus larvae

Decapod crustaceans have adopted a full range of reproductive strategies from the release of large numbers of small eggs (Penaeoidea) to the release of relatively low numbers of large advanced larvae (Nephropidae). As larval size determines trophic position in planktonic food webs, all food sources from phyto- to zooplankton are exploited, with many species changing trophic level during ontogenetic development. Comparative studies on digestive enzymes, levels of activity and changes during ontogeny, together with measurements of gastroevacuation rates and food energy values appear to reveal a general pattern. While herbivorous decapod larvae adapt to low food energy values with high enzyme activity levels, rapid food turnover and low assimilation efficiency, carnivorous larvae exhibit low levels of enzyme activity but compensate by extending retention time of high-energy food to maximise assimilation efficiency. New studies on digestive enzyme levels during development in the penaeid Litopenaeus vannamei, the caridean Lysmata debelius and the cirriped Elminius modestus, appear to agree with previous observations.

Ontogenetic change in digestive enzyme activity during larval development of Macrobrachium rosenbergii

Abstract Penaeus japonicus larvae were reared using live food, an artificial diet or an artificial diet plus C. gracilis . Larvae from all treatments were equivalent in weight and length at the third protozoeal stage, but mysis and postlarvae from both the live food and the artificial diet plus C. gracilis treatments were significantly larger and reached metamorphosis earlier than those fed the artificial diet alone. There were significant increases in percentage nitrogen and carbon contents during development in larvae fed the live food or the artificial diet plus C. gracilis , but not of larvae fed the artificial diet alone. High growth and nitrogen and carbon retention in mysis larvae fed live food was accompanied by a drop in trypsin activity. Despite a strong trypsin response to the artificial diet, mysis larvae appear unable to assimilate sufficient dietary protein to support growth equivalent to that observed in larvae fed live food. Supplementing the artificial diet with a low density of C. gracilis produced postlarvae of the same size and tissue composition as those reared using live food. It is suggested that the algal co-feed contributes either extra digestible nutrients or some specific growth-enhancing factor(s).

Halophyte filter beds for treatment of saline wastewater from aquaculture

Abstract This study was conducted to determine the ontogenetic changes in trypsin, non-specific esterase and amylase activities in Macrobrachium rosenbergii during larval development. Two batches of M. rosenbergii larvae were reared separately in 300-l tanks at 50 larvae l −1 . Rearing temperature and salinity were maintained at 30±2°C and 12 ppt, respectively. The larvae were daily fed with newly hatched Artemia nauplii at 5 nauplii l −1 . Trypsin, esterase and amylase activities in the larvae were estimated using TAME, butyrylthiocholine iodide and corn starch, respectively, as substrates. The results showed that maximum peaks of trypsin and esterase activities occurred at stage V–VI. Amylase activity remained low until the larvae reached stage VI–VIII, indicating that the early-stage M. rosenbergii larvae are exclusively carnivorous. Maximum amylase activity was observed at stage XdashXI. In general, the ontogenetic digestive enzyme activities in developing prawn larvae seemed to coincide with hepatopancreas development.

Seasonal abundance and recruitment in an estuarine population of mud crabs, Scylla paramamosain, in the Mekong Delta, Vietnam

The expansion of aquaculture and the recent development of more intensive land-based marine farms require efficient and cost-effective systems for treatment of highly nutrient-rich saline wastewater. Constructed wetlands with halophytic plants offer the potential for waste-stream treatment combined with production of valuable secondary plant crops. Pilot wetland filter beds, constructed in triplicate and planted with the saltmarsh plant Salicornia europaea, were evaluated over 88 days under commercial operating conditions on a marine fish and shrimp farm. Nitrogen waste was primarily in the form of dissolved inorganic nitrogen (TDIN) and was removed by 98.2 ± 2.2% under ambient loadings of 109-383 μmol l(-1). There was a linear relationship between TDIN uptake and loading over the range of inputs tested. At peak loadings of up to 8185 ± 590 μmol l(-1) (equivalent to 600 mmol N m(-2) d(-1)), the filter beds removed between 30 and 58% (250 mmol N m(-2) d(-1)) of influent TDIN. Influent dissolved inorganic phosphorus levels ranged from 34 to 90 μmol l(-1), with 36-89% reduction under routine operations. Dissolved organic nitrogen (DON) loadings were lower (11-144 μmol l(-1)), and between 23 and 69% of influent DON was removed during routine operation, with no significant removal of DON under high TDIN loading. Over the 88-day study, cumulative nitrogen removal was 1.28 mol m(-2), of which 1.09 mol m(-2) was retained in plant tissue, with plant uptake ranging from 2.4 to 27.0 mmol N g(-1) dry weight d(-1). The results demonstrate the effectiveness of N and P removal from wastewater from land-based intensive marine aquaculture farms by constructed wetlands planted with S. europaea.

Evaluation of hatchery-based enhancement of the mud crab, Scylla spp., fisheries in mangroves: comparison of species and release strategies

Artisanal fisheries for mud crabs are an important source of income in coastal communities of the Mekong Delta. However, populations are subject to pressure from increasing fishing effort to provide seed crabs for pond culture, as well as diminishing mangrove habitats. In the present study, Scylla paramamosain was found to be the dominant mud crab species within an estuarine mangal system, representing over 96.8% of mud crab fishery landings between February 1998 and March 1999. S. olivacea was also present in relatively low abundance (3.2% of landings). Analysis of catch-per-unit-effort (CPUE) data collected throughout 1997 and 1998, for an intertidal hand-fishery, shows that mud crabs were present in a fairly narrow range of mean abundance throughout the year, despite protracted periods of freshwater conditions during the rainy season. Recruitment of juvenile S. paramamosain (3–4 cm carapace width) was continuous through 1998, with a significant peak at the beginning of the dry season. No juvenile S. olivacea (< 5 cm carapace width) were found during the study. The mangal appears to provide a nursery habitat for S. paramamosain, with predominantly juveniles and sub-adults present, while a higher proportion of adults were recorded in the sub-tidal component of the population. Mature females were present throughout the year, with a peak in September–October 1997. The CPUE analysis provides a baseline of seasonal variation in crab abundance that can be used to monitor the effectiveness of resource management and potential impacts of future changes in habitat.

Effect of different diets on proteolytic enzyme activity, trypsinogen gene expression and dietary carbon assimilation in Senegalese sole (Solea senegalensis) larvae

Ranching, stock enhancement and restocking are management approaches involving the release of wild or hatchery-bred organisms to enhance, conserve or restore fisheries. The present study, conducted from April 2002 to November 2005, evaluated the effectiveness of releasing wild and hatchery-reared (HR) mud crabs in the mangroves of Ibajay, Aklan, Philippines where preliminary studies demonstrated declining fishery yields, abundance and size of crabs. Comparison of survival and growth of wild-released and HR Scylla olivacea and HR Scylla serrata demonstrated the effect of nursery conditioning, size-at-release and species differences. Overall yield and catch per unit effort (CPUE) increased by 46% after stock enhancement trials. Recapture rates of released crabs were highest in wild-released S. olivacea and in crabs measuring 65.0–69.9 mm carapace width (CW) and lowest in non-conditioned HR S. serrata. Growth rates were highest for conditioned HR S. olivacea and lowest for conditioned HR S. serrata (11.7 and 3.7 mm month–1 respectively). Fishing mortality was highest for S. olivacea, whereas natural mortality was greater for S. serrata. Conditioning hatchery-bred animals before release is also important in obtaining higher survival. S. olivacea was the more appropriate of the two species for release in mangrove habitats inundated with low-salinity water. However, there is a need for site-specific studies to evaluate the effectiveness of releases.