Crustacean Production Research Articles

Farming the waters: Bringing aquatic plant and animal species to agriculture

Aquaculture has a long history, with carp culture in Asia starting before 2000 BC and oyster culture in the Roman Empire before the time of Julius Caesar. However, it is clearly the past 40 yr that have seen the most dramatic expansion of aquaculture. The world's population now exceeds 6 billion people and is still growing at an alarming rate. The world's wild fish harvest has clearly peaked at or above the maximum sustainable yield of about 90 million t. Many fish stocks are suffering from over-fishing and there is little hope of any increase in the capture fisheries production. Though modern agricultural practices have been very efficient at increasing the per acre yields, the world is experiencing an alarmingly steady decrease in the amount of agricultural land devoted to food production. In the past 20–30 yr production of fish, molluscs, crustaceans and aquatic plants (aquaculture) has become an increasingly important means of producing food, and in some countries aquaculture production accounts for more than half of the total fishery harvest and is even as high as 90% in a few countries. I have reviewed the historical growth of aquaculture, compared the product value in various countries and reviewed aquaculture practices for a number of plant, molluscan, crustacean and fish species around the world. These culture technologies were compared and contrasted with agricultural practices. Finally, some predictions for the future of aquaculture development in Canada and the world have been made. Key words: Canadian aquaculture, history, salmon, fish farming, production statistics, fish culture technology

Release of the enzyme chitobiase by the copepod Temora longicornis:characteristics and potential tool for estimating crustacean biomass production in the sea

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 196:195-206 (2000) - doi:10.3354/meps196195 Release of the enzyme chitobiase by the copepod Temora longicornis: characteristics and potential tool for estimating crustacean biomass production in the sea Swier S. Oosterhuis*, Martien A. Baars, Wim C. M. Klein Breteler Department of Biological Oceanography, Netherlands Institute for Sea Research (NIOZ), PO Box 59, 1790 AB Den Burg, Texel, The Netherlands *E-mail: oosterh@nioz.nl ABSTRACT: The chitinolytic enzyme chitobiase (N-acetyl-β-d-glucosaminidase), which is expressed during the pre-moult phase of crustaceans, is released into the ambient water after shedding of the exuvium. We examined the potential use of chitobiase activity in water samples as a measure of secondary production of crustaceans. Chitobiase activity, expressed on the substrate 4-methylumbelliferyl-N-acetyl-β-d-glucosaminide (MUFNAG), was measured in experiments with the marine copepod Temora longicornis, with focus on the dissolved (Œfree¹, <0.2 µm) fraction. Significant activity of free chitobiase was found in the ambient water of individual copepodites when they moulted to enter the next stage. The activity of the chitobiase released was linearly related to body weight and to the increment of body weight. In bacteria-poor water (filtered through 0.2 µm), no significant decrease of free T. longicornis chitobiase occurred in the first 24 h. In non-manipulated water, the decay of free T. longicornis chitobiase by bacteria was exponential with time, with relative rates varying by 4 to 13% h-1 at 15°C. The particle-bound chitobiase activity was related to the number of bacteria. Different sources of chitobiase could be distinguished by enzyme characteristics. The Km value of T. longicornis chitobiase was 55 µmol l-1, comparable to values published for Daphnia species. In Oxyrrhis marina, a heterotrophic dinoflagellate serving as the main food item in the T. longicornis culture, enzyme assays indicated a Km < 0.2 µmol l-1. Water predominantly containing bacteria showed a Km > 100 µmol l-1. The usefulness of free chitobiase as a natural tracer of secondary production was tested in a culture vessel of T. longicornis. The rate of chitobiase release was derived from the chitobiase activity in the ambient culture water over time and the rate of decay in water samples devoid of copepods. From the relation between release of chitobiase and increase of body weight of moulting copepodites, the total daily biomass increase in the culture vessel was calculated. These estimates compared well with classical monitoring of biomass changes. If this relation found in T. longicornis is representative of marine crustaceans in general, tracking of free chitobiase in water samples could be a biochemical tool for estimating in situ secondary production in natural waters. KEY WORDS: Marine zooplankton · N-acetyl-β-d-glucosaminidase · Chitobiase · 4-methylumbelliferyl-N-acetyl-β-d-glucosaminide · Secondary production · Temora longicornis Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 196. Publication date: April 18, 2000 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 2000 Inter-Research.

Food safety and products from aquaculture

Aquaculture is currently one of the fastest growing food production systems in the world with production increasing at an average rate of 9.6% per year over the past decade. As world fish stocks are reaching the limits of exploitation, we shall rely to a far greater extent on products from aquaculture as food sources of high nutritional value. Approximately 90% of global aquaculture production is based in Asia, where it provides an important source of dietary animal protein of the region and income for millions of small-scale farmers. Commercial aquaculture contributes significantly to the economies of many producing countries, where highly valued species are a major source of foreign. Many different aquaculture systems exist world wide, ranging from small family-sized fish ponds to intensive cage culture industries as used in salmon fishing. There has been an expansion in the use of integrated farming systems, especially in Asia, where animal and human faeces are used to fertilise ponds. This paper will review global aquaculture systems used in the production of finfish and crustaceans and will focus on potential hazards arising from biological contamination of products that pose risks to public health.

Pond water aeration systems

During the past decade, pond aeration systems have been developed which will sustain large quantities of fish and invertebrate biomass. These aeration systems are modifications of standard wastewater aeration equipment. Aeration-performance testing has been important in selecting design features to provide cost-effective yet efficient aquaculture pond aerators. Paddlewheel aerators and propeller-aspirator-pumps are probably most widely used. Amounts of aeration vary from as little as 1–2 kW ha−1 in some types of fish culture to as much as 15 or 20 kW ha−1 in intensive culture of marine shrimp. Calculations suggest that about 500 kg additional production of fish or crustaceans can be achieved per kW of aeration. Aerators usually are positioned in ponds to provide maximum water circulation. This practice can result in erosion of pond bottoms and inside slopes of embankments, and accumulation of sediment piles in central areas of ponds where water currents are weaker. Recent studies suggest that the use of heavy aeration to provide the greatest possible production is less profitable than moderate aeration to improve water quality and enhance feed conversion efficiency. Automatic devices to start and stop aerators in response to daily changes in dissolved oxygen (DO) concentrations are improving, but they are expensive and not completely reliable. Augmentation of natural supplies of DO in ponds often is necessary to prevent stress or mortality of fish and crustaceans when DO concentrations are low. Several procedures have been used in attempts to increase DO concentrations in ponds. These methods include exchanging part of the oxygen-depleted pond water with oxygenated water from a well, pond, or other source, application of fertilizer to stimulate oxygen production by photosynthesis of aquatic plants, additions of compounds which release oxygen through chemical reactions, release of pure oxygen gas into pond waters, and aeration with mechanical devices which either splash water into the air or release bubbles of air into the water. Water circulation devices also enhance DO supplies in ponds by mixing DO supersaturated surface waters with deeper waters of lower DO concentration. This reduces the loss of oxygen from ponds by diffusion. Also, when surface waters are not saturated with DO, water circulation causes surface disturbance and enhances oxygen absorption by the water. Mechanical aeration is by far the most common and usually the most effective means of increasing DO concentrations in ponds. In semi-intensive aquaculture, aeration is applied on an emergency basis. Farmers check DO concentrations, and when low concentrations of DO are expected, aeration is applied. In intensive aquaculture, aeration is applied each night or even continuously. The purpose of this article is to summarize the ‘state of the art’ of mechanical aeration of aquaculture ponds.

Differences in composition of small, motile invertebrate assemblages from seagrass and unvegetated habitats in a southern Australian estuary

Assemblages of small, motile invertebrates (epifauna) from eelgrass(Zostera muelleri) and unvegetated habitats in a shallow, marine-dominatedestuary were compared at five sampling periods over one year. Assemblagesbased on abundance and biomass of 21 taxa from the two habitats groupedseparately in multivariate analyses (MDS ordination), and these groupingswere shown to be significant using an analysis of similarities (ANOSIM)randomisation routine. Secondarily to habitat differences, weak influencesof water temperature and distance to open water, but not of salinity, weredetected at some periods. Abundance and biomass of key taxa and all speciescombined were higha in eelgrass than in unvegetated habitat. Cumaceans wereexceptional in being collected predominantly from unvegetated habitat. Totalepifaunal production and crustacean production estimated using twovariables, (1) the biomass of individuals of each size class, and (2) watertemperature, were also higher in eelgrass than in unvegetated habitat. Thehigher abundance in eelgrass of taxa such as amphipods, harpacticoidcopepods and polychaetes that are major components of the diets of smallfish is consistent with a model explaining higher fish numbers in eelgrassin terms of prey availability.

Nutritional studies in crustaceans and the problems of applying research findings to practical farming systems

Methodological approaches for undertaking research on the dietary nutrient requirements of farmed crustaceans should ensure that the studies are designed and conducted in such a manner that the ensuing results can be applied under practical farming conditions. Sadly, the majority of studies to date have had little practical applicability, the bulk of nutrient-requirement studies having been conducted under controlled, artificial, laboratory conditions. Despite the fact that the giant tiger prawn (Penaeus monodon Fabricius), the whiteleg shrimp (Penaeus vannamei Boone) and the fleshy prawn (Penaeus chinensis Osbeck) are the three most-cultivated crustacean species in the world (total aqua-culture production of these crustacean species in 1993 totalled 625487 metric tonnes or 66.9% of the total world farmed crustacean production), little or no information exists concerning their dietary nutrient requirements under practical semi-intensive pond-farming conditions (where the bulk of the production is currently realized). To a large extent this has been due to the apparent reluctance of the conventional laboratory-based crustacean nutritionist to also work under field conditions and the difficulty of quantifying the contribution of natural food organ-isms in the overall nutritional budget of pond-raised crustaceans. If meaningful conclusions are to be drawn from nutrient requirement studies and dietary feeding trials, it is essential that the experimental animals be reared under conditions mimicking as far as possible those of the intended farm production unit and environment, including holding facility (indoor or outdoor tank, cage or pond), feed preparation technique (grinding, pelleting, drying; diet texture, form, shape, size, buoyancy and water stability), feeding method (hand, demand or automatic feeding; feeding frequency and feeding rate–fixed or satiation feeding; day or night-time feeding), water quality (temperature, turbidity, salinity, oxygen and mineral concentration; water exchange rate, water circulation pattern and artificial aeration), photoperiod (artificial or natural) and crustacean stocking density. Finally, but not least, it is essential that the growth performance of the experimental animals be at least equal to or greater than that of the target crustacean species under practical farming conditions if realistic conclusions are to be drawn, and it is necessary that dietary nutrient requirements can be ascertained under conditions of maximum attainable growth.

The production and trophic ecology of shallow-water fish assemblages in southern Australia II. Diets of fishes and trophic relationships between fishes and benthos at Western Port, Victoria

A total of 5113 fishes belonging to 91 species was collected from seagrass and unvegetated habitats at Western Port for dietary analysis between August 1989 and November 1990, with 720 animals having empty guts. None of the common species was found to have a highly specialised diet. Crustaceans were the dominant component in the diets of the majority (69%) of the 88 species with non-empty guts, with five species (a girellid, a mugilid, a monacanthid and two gobiids) consuming large amounts of algal material, and only one species [the garfish Hyporhamphus melanochir (Valenciennes)] ingesting seagrass in any quantity. In general, dietary differences between juveniles and adults of a species were as great as dietary differences between fish belonging to different species when at the same body size. Amongst the crustacean feeders, diets generally changed from predominantly copepods to predominantly peracarids (amphipods, isopods and mysids) at ≈0.1 g wet body weight, and from predominantly peracarids to predominantly crabs and shrimps at ≈100 g. Across the range of species examined, there was a close relationship between the size of ingested prey and fish biomass. Prey length averaged 7.5% of predator length. The dominant species in gillnet catches, the mullet Aldrichetta forsteri (Cuvier & Valenciennes), possessed an unusual diet because prey were smaller than for other fishes of the same body size and large quantities of algal material were also consumed. Similar trophic pathways leading to fishes were found in different habitats, with the major linkages being from benthic microalgae and detritus through epifaunal crustaceans to the smaller fishes. The major predators of small fishes were locally-resident species, the rock flathead Platycephalus laevigatus Cuvier & Valenciennes in seagrass beds and the sand flathead Platycephalus bassensis Cuvier & Valenciennes at unvegetated sites. Crustaceans supplied most of the dietary intake for the small fish communities at all sites, with molluscs and polychaetes also important but supplying >25% of food consumed at only two sites. When daily rates of consumption were compared with daily production of food, the production of crustaceans >1 mm sieve size was calculated to be all consumed by fish. The production of the non-crustacean benthos was an order of magnitude higher than that consumed by fish predators. These results indicate that the availability of high quality crustacean prey may limit the production of fishes, and that fishes are likely to compete diffusively for crustacean prey. Additional support for this hypothesis is provided by the observations that the condition of seagrass-associated fish declined, and mortality rates were high, during the autumn season when total fish consumption could not be supported by crustacean production.

The production and trophic ecology of shallow-water fish assemblages in southern Australia III. General relationships between sediments, seagrasses, invertebrates and fishes

Fishes and benthic invertebrates were sampled in seagrass and unvegetated habitats at 14 localities across southern Australia in order to determine any consistent relationships between animal production, fish consumption and environmental parameters over a large spatial scale. Most of the features identified in a related study at Western Port were confirmed over the extended geographic range; however, an exception was that the production of fishes in the smallest size-classes (i.e. <1 g wet weight) was not consistently greater in seagrass habitat than unvegetated habitat. The more important characteristics of seagrass and unvegetated habitat types identified in the extended study were (1) more fish species were associated with seagrass habitat than unvegetated habitat, (2) the majority of small-fish species in both habitat types fed on crustaceans, with relatively few species capable of utilising algae and virtually no species utilising seagrass, (3) the few species that did ingest algae often occurred in high abundance, (4) the size of prey eaten by fishes increased consistently with fish size, with prey length averaging ≈6% of fish length, (5) abundant large fish species generally consumed smaller prey than rarer large fish species at the same body size, (6) greater benthic invertebrate and demersal fish production occurred in seagrass habitat than in unvegetated habitat, (7) most of the production of crustaceans >1-mm sieve size was ingested by fish predators while only a small proportion of non-crustacean benthic production was consumed. Fish production was highly correlated with crustacean production and seagrass biomass, and was negatively correlated with wave exposure (measured as fetch) across the range of sites. The estimated production of crustaceans was highly correlated with the biomass of seagrass material and also with the proportion of particles <63 μm in the sediments. The overall relationships between macrofaunal production ( M; mg · m −2 · day −1), macrocrustacean production ( C; mg · m −2 · day −1), demersal fish production ( D; mg · m −2 · day −1), fetch ( F; km), seagrass biomass ( L; g · m −2), proportion of particles <63 μm ( S;%) and temperature ( T; °C) were: ln M = 1.41 + 0.088 ln ( L + 1) + 0.38 ln S + 0.89 ln T, ln C = −0.93 + 0.27 ln ( L + 1) + 0.22 ln S + 0.89 ln T, ln D = −1.23 − 0.62 ln F + 0.36 ln ( L + 1) + 1.04 ln T. These regression equations can be used as models to predict the production of macrofauna, crustaceans and small fishes at unexamined sites. When predictions were compared with estimates of annual production at the eight sites previously examined in Western Port, most predictions lay between 50 and 200% of measured values. Additional work in Australia and overseas should allow these models to be refined.

The production and trophic ecology of shallow-water fish assemblages in southern Australia I. Species richness, size-structure and production of fishes in Western Port, Victoria

Fishes were sampled by seine and gillnet in three different habitat types (seagrass, unvegetated sediment and channel) within Western Port, Victoria, between 1989 and 1990. Approximately twice as many fish species were collected per seine haul from seagrass habitat ( x ̄ = 8.7 ) compared with intertidal unvegetated habitat ( x ̄ = 4.7 ), while relatively few fish species were collected per haul from deeper unvegetated-channel habitat ( x ̄ = 2.3 ). Most fishes associated with seagrass beds were widely distributed within the embayment, with the notable exception of a number of coastal species that occurred in low numbers at a single site (Cowes Bank seagrass) near the entrance to the bay and had presumably drifted as pelagic larvae from reefs outside. Small fishes (<10 g weight) were more abundant in seagrass than in unvegetated habitats; however, relatively few of these animals were juveniles of commercially fished species. Seagrass beds in Western Port were not found to provide a significantly more important nursery habitat for commercial species than unvegetated habitat. The production of small fishes at different sites was highly correlated with the production of epifauna, particularly crustaceans. We postulate that these factors are causally linked. This hypothesis is supported by seasonal data, which indicate that when the production of crustaceans was at its lowest during May, populations of small fishes were rapidly declining in Western Port, either by dying or emigrating. Seagrass beds supported over twice the production of small fishes as unvegetated habitat (3.82 g · m −2 · yr −1 cf. 1.58 g · m −2 · yr −1 in unvegetated habitat). Because an estimated 178 km 2 of seagrass habitat has been lost from Western Port since 1973, the reduced production of fishes in unvegetated habitat translates to a decline in small fish production of 6̃30 tonnes AFDW per year. However, falling catches of only two commercial fishes, six-spined leatherjackets ( Meuschenia freycineti) and blue rock whiting ( Haletta semifasciata), were clearly associated with seagrass loss, with most of the loss of fish production occurring amongst small non-commercial species, particularly syngnathids, clinids and scorpaenids. Differences in production of small fishes between habitats were not reflected higher in the food chain. Although greater numbers of fishes were collected using small-mesh (64 mm) gillnets from seagrass than unvegetated habitats, these differences were due to variation in the catch of the omnivorous mullet Aldrichetta forsteri, the most abundant species, rather than variation in the abundances of piscivorous fish species. No differences were found between catches of fish using large-mesh (108 mm) gillnets placed in different habitats.

Atkinsiella parasitica sp. nov. isolated from a rotifer, Brachionus plicatilis

A new species ofAtkinsiella (Lagenidiales, Oomycetes),Atkinsiella parasitica is described and illustrated. It was isolated from the eggs and bodies of a rotifer,Brachionus plicatilis, with fungal infection in 1992. The rotifer was reared in a hatchery as the first food supply for seed production of crustaceans and fishes. The fungus is characterized by producing monoplanetic, lateral biflagellate zoospores, and infrequently branched discharge tubes. Optimum temperature for the fungus was 25°C. The fungus was considered an obligate marine fungus, because its growth was observed only on PYGS medium including seawater.

Antibody‐based methods for assessing seafood authenticity

Immunoassays have been developed to facilitate authenticity testing of fish and seafood products. Three specific authenticity issues were addressed: substitution of canned sardine with other species, adulteration of canned tuna with bonito and adulteration of reformed crustacean meat with white fish. Antisera were raised to water‐soluble protein extracts of canned sardine and canned tuna and, where appropriate, their specificities were adjusted using simple blocking and/or immunoadsorption methods. The antisera were used to construct several immunoassays, one of which allowed discrimination between canned sardine and non‐sardine meat, and could be used to detect substitution of whole sardines with non‐sardine species. A second set of assays allowed discrimination between fish and crustacean meat, and should allow the detection of fish in crustacean products. However, with a third set of immunoassays, only limited discrimination between bonito and tuna could be achieved and these assays require further development.

Marine crustacean farming: present status and perspectives

Resume Laubier A., L. Laubier. Aquat. Living Resour., 1993, 6, 319-329. For centuries, several species of prawns and crabs have been raised from wild-caught juveniles in coastal brackish-water fish ponds in various countries of south east Asia. The Indonesian tambaks are well known examples of such traditional practices. In western countries, since the turn of the century, advances of marine biology and fast increase of marine fisheries enabled the development of large-scale production and release of larval stages of Amencan and European lobsters in a fruitless attempt to restock natural populations. After the Second World War, the increasing demand for crustaceans in United States and Japan was satisfied by opening new prawn fisheries al1 over the world. A major breakthrough was achieved with the development of hatchery technologies for the penaeid prawn Penaeus japonicus (Hudinaga, 1942 in Japan) and the caridean prawn Macrohrachium rosenbergii (Ling, 1969 in Malaysia), which occurred during the first decades of the second half of this century. Together with the increasing market demand in developed countries for sea food, this led to a considerable interest of both public agencies and pnvate investors in marine shrimp and prawn culture. In western countries, a large number of pioneering commercial ventures, often based on assumptions not scientifically founded, failed. Nevertheless, the aquaculture production of prawns mainly based on wild-caught juveniles increased in South-East Asia and Central America during the 1980s. This overall positive trend should not hide important failures which occurred at a local scale, such as the Taiwanese crisis of 1988 due principally to environmental degradation, resulting in severe disease problems and a near collapse of the farming activity. Following the early period of hatchery technology development, the major scientific achievements were related to food requirements and formulation of compound diets for larvae, juveniles and adults and to a better knowledge of diseases caused by bacteria and several viruses which have been identified from hatcheries and intensive farming ponds. Additional new technological advances have emerged from recent research in the fields of physiology (endocrinology) and genetics. By far, the major part of the world production of marine crustaceans relies on penaeid prawns and, to a lesser extent, on Macrobrachiurn species. However, some other species of marine crustaceans have potential for aquaculture. The economic aspects of marine crustacean aquaculture should be considered together with those of the fishing industry: market prices are rather similar, depending on the quality of the product. The balance between market demand and production is an important constraint which, in tum, establishes the success of prawn farming. Since the early 1980s, crustacean aquaculture has increased tremendously in both Asia and America: the world production for 1991 approximated 700,000 tons, with more than 600,000 tons from penaeid prawn culture.

Effects of Impoundment and Diversion on the Crustacean Plankton of Southern Indian Lake

Planktonic crustaceans in Southern Indian Lake were surveyed in 1972 before impoundment, during 1975 when water levels rose above the recorded high level, and then annually from 1977 to 1980 after full impoundment and diversion. Synoptic data were collected in each of these years in midsummer during July or August from a set of 53 stations covering all regions of the lake. Vertical hauls were made at each station using twin nets of 77-μm mesh and 25-cm mouth diameter. In 1972, the crustacean plankton fauna of Southern Indian Lake was composed mainly of 15 copepod and 15 cladoceran species. At least 25 of these species were truly pelagic, while 5 were littoral. Cyclopoids comprised 46% of total crustacean abundance, calanoids 33%, and cladocerans 21%. Dominant species within these three groups were Cyclops bicuspidatus thomasi (37.6% of total abundance), Diaptomus ashlandi (20.1%), and Chydorus sphaericus (8.9%). Total abundance averaged 76 individuals (ind)∙L−1, comparable to more southerly waters such as Lake Ontario (80 ind∙L−1) and Lake Winnipeg (53–108 ind∙L−1) (K. Patalas. 1975. Int. Ver. Limnol. Verh. 19: 504–511). Throughout the lake, total crustacean abundances varied from 10 ind∙L−1 near the Churchill River inflow to between 100 and 200 ind∙L−1 in a few well protected areas. From 50 to 100 ind∙L−1 occurred within the main body of Southern Indian Lake. In 1975, an unusually high water year, lake mean plankton abundance was 61 ind∙L−1. Following diversion in 1976, no dramatic changes in species composition were observed. However, the mean abundance of crustaceans decreased to 40–46 ind∙L−1 during the period 1977–80. Regional zooplankton responses were varied. No significant changes occurred in areas adjacent to the Churchill River inflow, with pre- and post-diversion densities being 35 and 36 ind∙L−1, respectively. In the main water bodies north of the diversion route, abundances declined by 60% and biomass by 50%. A 2–3 °C drop in northern basin water temperatures, related to diversion, reduced growth rates by approximately 20% and resulted in a 60% decline in crustacean production. Not all groups of crustaceans responded similarily to impoundment and diversion. Lakewide average numbers of cladocerans declined from 16 to 4 ind∙L−1 and the area of their distribution was reduced particularly in northern regions of the lake following impoundment. Cyclopoids declined from 35 to 16 ind∙L−1 but showed no change in their distribution. These reductions were related to decreased water temperatures, lower midsummer chlorophyll a concentrations, and decreased water transparencies. The mean abundance of calanoids as a group did not change, but the abundance and distribution of individual species were variably altered. Smaller calanoid species showed either no change or a decrease in their numbers and distribution. Larger species, e.g. Limnocalanus macrurus, Senecella calanoides, and Diaptomus sicilis, were significantly more abundant and widespread following diversion. Similar increases in Mysis relicta were also observed. These large species, preferred food items for both whitefish and cisco, are cold stenotherms, inhabiting deeper water layers. Their increased abundance is likely associated with decreased water transparency offering better protection against predatory fish, decreased water temperature creating more favorable conditions, and increased water depth enlarging the volume of deeper waters suitable for these species.

Economic management of lagoons

Abstract Economic management of lagoons can lead to greater production of fish, shellfish, crustaceans and other food animals, and in tourist areas, to greater production of ornamental corals. Increased production of molluscs could be achieved by culture methods. Chaetoceros armatus is suggested. Australia and New Zealand lead the world in economic agriculture production. Tropical Australia is far behind in producing food from the sea. Unpractical conservation policies may be the cause.

Biotechnology in the Marine Sciences

Genetic engineering applied to the production of fish, molluscs, algae, algal products, and crustaceans in natural environments and hatchery systems is still at the rudimentary stage. Cloning systems for producing commercially important chemicals, pharmacologically active compounds, and metamorphosis-stimulating substances present in marine organisms are being sought. Attempts are being made to develop useful drugs from the sea, including antineoplastic, antibiotic, growth-promoting (or -inhibiting), analgesic, and antispasmodic agents. Immediate commercial applications can be expected from engineered systems involving polysaccharide and specialty chemical production, with marine microorganisms as the source of genetic material.

FILTRATION TECHNIQUE FOR RECIRCULATING AQUACULTURE SYSTEMS

ABSTRACTThe use of biological filters in closed systems to maintain salmonids and crustaceans is becoming more common as commercial aquaculture ventures approach the urban marketplace. Competition for land and water resources makes the capital costs for equipment, tanks, and material economically feasible. The advantages of intensive closed system aquaculture are greater control over water quality, more production per unit area, and controllable growth rates. The feeding techniques and high loadings generally produce a concentrated wastewater that must be treated by physical, chemical, and biological processes before reuse. Treatment of ammonia, nitrite, and suspended solids are the primary concerns of the culturist. This paper describes the removal efficiencies of biological sand filters in commercial service for various loading parameters. Design factors and the ranges of operation for different systems and organisms are related to data collected over two years of culture. Particular attention is paid to the various soluble and solid forms of nitrogenous waste and their removal in prefiltration, submerged, and trickling biological oxidation systems. The recycled water is returned to many different tanks for polyculture production of fish and crustaceans.

Das pelagische Crustaceenplankton des Bielersees: Abundanzdynamik, Produktion und Sukzession

1. In 1974 the population dynamics and production of the crustacean plankton in eutrophic Lake Biel were investigated. Earlier papers concerning the crustacean fauna of Lake Biel enabled the succession to be followed qualitatively and partly quantitatively over the last 80 years. 2. The samples were collected between 0 and 70 m at the deepest station in the lake by means of a pump at intervals of 2 to 3 weeks. As the most important environmental factors, oxygen and temperature profiles were taken (fig. 4). In order to distinguish between the different copepodid stages of the various copepod species morphometric differentiating criteria were worked out (fig. 2 and 3). The calculation of crustacean production was made accroding to Mittelholzer [57]. The dry weight of single individuals was determined from the length measurements using the regression equations of Dumont et al. [7] (table 1). 3. The crustacean plankton was numerically dominated byCyclops vicinus lobosus (April/May), byDaphnia longispina hyalina (June/July) and byAcanthocyclops sp. (August/September) (fig. 16). The population maxima of these three species reached at times 1.2 million individuals per m2. In winterEudiaptomus gracilis dominated with a maximum of 100,000 individuals per m2. The density of the 4th copepodides ofC. vicinus lobosus in diapause (May 1974 to January 1975) was 600,000 individuals per m2 lake bottom (fig. 5). 4. The pelagic crustacean production in 1974 amounted to 26.2 g dry weight per m2. 81% of this was contributed by the three speciesD. longispina hyalina, C. vicinus lobosus andAcanthocyclops sp. the percentages of the total production for the individual species in 1974 were as follows:D. longispina hyalina 40.9%, C. vicinus lobosus 26.3%, Acanthocyclops sp. 13.7%,E. gracilis 5.9%, Bosmina sp. 5.1%,Mixodiaptomus laciniatus 2.4%, D. longispina galeata 2.4%, D. cucullata 1.3%, C. bohater 0.8%, C. abyssorum praealpinus 0.7%, Mesocyclops leuckarti 0.5%. This crustancean production output lies in the same order of magnitude as that of other eutrophic lakes. 5. Since 1900 the composition of the crustacean species has changed basically both in quality and quantity (table 7):

Distribution and Production of Two Crustaceans in a Wetland Pond

Annual production of the isopod, Asellus obtusus, and the amphipod, Crangonyx gracilis sp., in a small wetland pond in NW Georgia was estimated using the Hynes method. Both species were found in two distinct vegetation zones: a central Cephalanthus occidentalis zone and a marginal Nyssa biflora zone. In the Nyssa zone, the crustaceans occurred in the aufwuchs and benthos, but in the Cephalanthus zone, only in the aufwuchs. Five samples were taken each month in each of these three habitats during one year to obtain life history and standing stock data. Although growth of each species was relatively asynchronous, they each appeared to have one generation per year. Combined aufwuchs-benthos production in the Nyssa zone was 2.44 g/m2 dry wt for Crangonyx and 1.44 g/m2 for Asellus. Annual turnover ratios were 6.1 and 6.0, respectively. Aufwuchs production in the Cephalanthus zone was 1.63 g/m2 for Crangonyx and 0.65 g/m2 for Asellus. Annual turnover ratios were 6.8 and 8.1, respectively. Benthos in Nyssa contributed by far the greatest crustacean production to this zone based upon standing stock values, but aufwuchs populations were the only significant source of production in the Cephalanthus zone.

Health Problems in Packing Crustacean Products

Health Problems in Packing Crustacean Products