Shrimp (Litopenaeus vannamei) production and stable isotope dynamics in clear‐water recirculating aquaculture systems versus biofloc systems

Closed recirculating aquaculture systems (RAS) offer advantages over traditional culture methods including enhanced biosecurity, the possibility of indoor, inland culture of marine species year‐round and potential marketing opportunities for fresh, never‐frozen seafood. Questions still remain regarding what type of aquaculture system may be best suited for the closed‐system culture of marine shrimp. In this study, shrimp (Litopenaeus vannamei) were grown in clear‐water RAS and in biofloc‐based systems. Comparisons were made between the system types with respect to water quality, shrimp production and stable isotope dynamics used to determine the biofloc contribution to shrimp nutrition. Ammonia and nitrite concentrations were higher, and shrimp survival was lower in the biofloc systems. Although stable isotope levels indicated that biofloc material may have contributed 28% of the carbon and 59% of the nitrogen in shrimp tissues, this did not correspond with improved shrimp production. Overall, the water column microbial communities in biofloc systems may be more difficult to manage than clear‐water RAS which have external filters to control water quality. Biofloc does seem to offer some nutritional contributions, but exactly how to take advantage of that and ensure improved production remains unclear.     

Recovery of Hafnia alvei from diseased brown trout,Salmo trutta L., and healthy noble crayfish,Astacus astacus (L.), in Bulgaria

Hafnia alvei was isolated in Bulgaria from healthy noble crayfish, Astacus astacus (L.), and then from farmed diseased brown trout, Salmo trutta L., with signs of haemorrhagic septicaemia. The isolates were identified initially with conventional phenotyping and commercial Merlin Micronaut and API 20E rapid identification systems, followed by sequencing of the 16S rRNA gene. Hafnia alvei Bt1, Bt2 and Aa4 were of low virulence to rainbow trout and brown trout, although cytotoxicity was demonstrated by Bt1 and Bt2, but not by Aa4.     

The effects of seasonal,sex and size on the digestive enzyme activities in freshwater crayfish (Astacus leptodactylus Eschscholtz, 1823)

The effects of seasonal, sex and size on digestive enzyme activities of Astacus leptodactylus in natural habitat were investigated in the present study. The freshwater crayfish were sampled 584 individual as seasonally from Egirdir Lake. Ten male and 10 female individuals were sampled randomly from caught crayfish in each two different size ranges (4.5–7.0, 7.1–9.9 cm) and each season. The gastrointestinal tract, gastric, intestine and midgut gland were individually dissected on ice for enzyme analysis and stomach contents. At the end of the study, amylase activities were affected by interaction of season × sex × size in intestinal, season × sex in midgut gland. However, any interaction was not determined in amylase activities of the gastric. Lipase activities were affected by interaction of season × sex × size in intestinal and gastric, season × sex in midgut gland. The protease activities in each organ were affected by interaction of season, sex and size (p ? .05). In all organs, amylase and lipase activities were similar. However, the highest protease activity was in stomach while the lowest protease activity was the intestine. The protease activities were higher than amylase and lipase activities. There is a positive correlation between protease enzyme activities in gastric with gonad maturation and active feeding period. It can be said based on data of digestive system and high protease activity that A. leptodactylus is an omnivore species in need high protein. In addition, the reason for the low levels of lipase activity may be A. leptodactylus not prefer high fat foods or not fed high fat foods.     

Effects of photoperiod and stocking density on survival,growth and physiological responses of narrow clawed crayfish (Astacus leptodactylus)

Photoperiod and stocking density are critical factors influencing the performance of decapod crustaceans in culture, however, their influence on growth; survival and biochemical physiology of crayfish broodstock have rarely been considered. Analysis of biochemical physiology in crayfish broodstock during the non‐breeding season provides information on the energy storage requirements of broodstock for increased survival and reproductive output. Growth rate, moulting frequency, survival and biochemical physiology were measured in Astacus leptodactylus broodstock that were cultured at three different photoperiods (18L:6D; 12L:12D; and 6L:18D) and three stocking densities (10, 20 and 40 individuals m^?2) during non‐breeding season. Survival of crayfish was highest at 18L:6D photophase and 10 m^?2 (100%) than other treatments. Survival in the high stocking density was high when combined with 18L:6D photophase, but weight gain (WG) and specific growth rate (SGR) were higher at shorter photophase and lower stocking density. Longer photophase (18L:6D) increased stress responses, characterized by increased haemolymph lactate and glucose levels. Stocking density did not affect proximate composition of crayfish; however, individuals cultured at 18L:6D photophase had higher lipid content than other photoperiod treatments. The study demonstrated that culturing A. leptodactylus at 18L:6D photophase and 10 m^?2 is critical for increased survival of broodstock.     

Ultraviolet light and semi‐recirculating systems in artificial incubation of noble crayfish (Astacus astacus) eggs: opportunities and limitations

Development of artificial crayfish egg incubation is a milestone in intensive culture of crayfish as commercially important freshwater animals. This study evaluated experimental treatments combining continuous UV lighting, a non‐chemical antifungal treatment, with an initial formaldehyde bath for noble crayfish (Astacus astacus) eggs incubated in semi‐recirculating systems, which requires less than 1 per cent the amount of water necessary for conventional flow‐through systems. The one‐time administration of a pre‐incubation bath to reduce formaldehyde exposure was ineffective. Ultraviolet irradiation of recirculating water provided poor results (13.5% and 35.2% final survival rates to stage 2 juveniles) and led to deteriorating water quality. An inability of hatchlings to successfully moult and the occurrence of limb deformities was observed in UV‐treated groups, and juvenile mortality was found across all experimental treatments.     

Estimating the human impact on populations of the endangered noble crayfish (Astacus astacus L.) in north‐western Poland

• 1. The Pomorskie Lakeland close to the town of Miastko shows the highest density of stocks of the noble crayfish Astacus astacus (L.) in the lowlands of north‐western Poland. In summer 2002, the present status of this highly threatened species was analysed by means of mark and recapture trapping.
• 2. Nine lakes with known occurrence of A. astacus were investigated. Each lake was surveyed with regard to the crayfish population density, water quality and potential recent and historical impact of fisheries and recreation. The estimated population density was evaluated statistically with respect to a set of potential environmental variables.
• 3. The estimated densities of A. astacus populations varied from very abundant (6.6 adult individuals per trap per night) to absent. Two lakes were found to contain the non‐indigenous crayfish Orconectes limosus (Raf.). The population density was not correlated with conductivity, pH, transparency, alkalinity, the concentration of ammonium, calcium, chloride, nitrate, nitrite, total nitrogen, total phosphorus, or with the trophic status of the lakes. A. astacus occurred in lakes ranging from mesotrophic to eutrophic.
• 4. The results suggest that both occurrence and density of A. astacus populations depended on criteria associated with human activities that have altered the aquatic environment. Abundance of A. astacus was negatively correlated with eel (Anguilla anguilla) stocking intensity (r = ?0.88; p < 0.01) and number of yearly net catches (r = ?0.66; p < 0.05) and positively correlated with distance to nearest town (r = 0.72; p < 0.05).
• 5. It is concluded that the introduction of O. limosus most likely resulted from fishery activities, emphasizing the need for regulations to reduce the negative impact of lake fisheries on native crayfish stocks.

Copyright © 2005 John Wiley & Sons, Ltd.     

Antifungal effect of Origanum onites essential oil as an alternative to formalin in the artificial incubation of narrow‐clawed crayfish (Astacus leptodactylus Eschscholtz, 1823)

As alternative to formalin, the antifungal effect of a plant product [Origanum onites L. (Lamiaceae) oil] was investigated for use in the artificial incubation of narrow‐clawed crayfish (Astacus leptodactylus Eschscholtz) eggs. For this purpose, this study was conducted as two experiments. In experiment I, the eggs were artificially incubated for 40 days. In experiment II, juveniles were cultured to determine effects of O. onites oil on juveniles for 30 days. The experimental groups were as follows: formalin (3500 ppm for 15 min), O. onites oil (300 ppm for 15 min, 700 ppm for 2 min and 1000 ppm as a dip treatment 15 split‐second) and a control (no treatment). In the experiment I, the highest hatching rate (86%) and survival rate of stage II juveniles (80%) were observed in 1000 ppm dip group. These results were similar to that of formalin group (85% and 79%) respectively. The control group exhibited the lowest hatching rate (49%) and stage II rate (42%) compared with the 1000 ppm dip group and 3500 ppm formalin treatments. However, other concentrations (300 and 700 ppm) of O. onites showed toxic effects on the eggs and there was no hatching. In the experiment II, the survival rate and growth performance of the crayfish juveniles were similar in all groups. This study indicated that the 1000 ppm O. onites dip treatment could be a good alternative to formalin for improved egg hatchability in the artificial incubation of crayfish eggs.     

Artificial incubation of noble crayfish (Astacus astacus) eggs in a partially recirculating system using formaldehyde as an antifungal treatment

There is little information on the long‐term artificial incubation of noble crayfish eggs. The present study evaluated artificial incubation in a partially recirculating system using formaldehyde baths as antifungal prophylaxis. Crayfish eggs were treated three times a week in a formaldehyde bath of 3000 ppm for 15 and 20 min and in 2500 ppm for 15, 20 and 25 min. In all treated groups, high final survival rates (87.8–92.0%) to stage 2 juveniles were obtained after 83 days. Significantly lower survival was observed in the control group (45.4%). It was concluded that recirculating systems can be used successfully for artificial incubation of crayfish eggs in order to conserve water. Formalin was found as an effective fungicide but its use should be carefully considered because of its safety issues for farm staff and environmental pollution.     

Effect of dietary supplementation of calcium chloride on growth,survival, moulting frequency and body composition of narrow‐clawed crayfish,Astacus leptodactylus (Eschscholtz, 1823)

The effects of dietary calcium chloride (CaCl₂) concentration on the growth, survival, moulting and body composition of Astacus leptodactylus were studied. Diets were prepared using supplementation of 0 (control), 30, 60 and 120 g kg^?1 calcium chloride commercial trout larvae diet containing 50% protein and 12% lipid. Astacus leptodactylus larvae with an average total length of 22.0 ± 0.05 mm (TL) and weight of 0.53 ± 0.01 g obtained from eighteen ovigerous females collected from Seydisehir Sugla Dam lake in Konya, Turkey, were stocked in 0.2‐m² aquariums at a rate of 50 crayfish m^?2 and reared for 90 days. The experiments included four treatments (diets) with three replicates each. Calcium chloride exerted positive effects on growth, moulting frequency, feed efficiency and survival of narrow‐clawed crayfish. Crayfish fed with 60 g calcium kg^?1 calcium chloride‐supplemented diet exhibited the highest weight gain and specific growth rate (SGR) but the lowest survival rate (63.3%) (P < 0.05). There were no significant differences (P > 0.05) in mean moisture (803.5 g kg^?1) and protein content (177.0 g kg^?1) in crayfish tail meat. However, lipid values were between 3.8 and 11.6 g kg^?1 and significantly different among the diets (P < 0.05). Diet with 60 g kg^?1 calcium chloride is recommended for the best growth of freshwater crayfish.     

The effects of dietary nucleotide content on the growth performance,digestibility and immune responses of juvenile narrow clawed crayfish,Astacus leptodactylus leptodactylus Eschscholtz, 1823

A 126‐day experiment was carried out under controlled conditions to compare the effects of five levels (0.5, 1.0, 1.5, 2.0 and 2.5 g kg^?1) of dietary nucleotide (Vannagen^®) on the growth performance and biological indices of juvenile crayfish (8.25 ± 0.39 g). The protein efficiency ratio (PER, 1.69–2.17), lipid efficiency ratio (LER, 2.29–3.00), energy efficiency ratio (EER, 2.68–3.65), protein productive value (PPV, 57.01–68.95%), lipid productive value (LPV, 63.02–75.15%) and energy productive value (EPV, 68.20–88.15%) increased significantly (P < 0.05) as linear response to increased dietary nucleotide from 0.5 to 2.5 g kg^?1 in the feed. With an increase in the dietary nucleotide, the uricase activity (654.29–827.63 U g^?1) and lactobacillus count to total count ratio (1.21–2.17) of crayfish fed the experimental diets increased significantly (P < 0.05). Crayfish fed the diets containing different levels of nucleotide (from 0.5 to 2.5 g kg^?1) had higher phenoloxidase activity (1.57–2.11 U min^?1) than that of control after air exposure challenge. At the levels tested, 2 g kg^?1 nucleotide in the diet was considered optimum for growth performance, digestibility and immune responses. It can be concluded that dietary nucleotide exerted positive effects on growth performance, feed utilization and accelerate crayfish immune response against air exposure challenge.     

Effects of feeding rates on the growth,water quality and nutrient budget of western king prawn (Penaeus latisulcatus Kishinouye) reared in recirculating aquaculture systems

Feed rate is one of the important variables considered for the improvement in production of prawns. The effects of four feeding rates on growth, water quality and the nutrient budget of Penaeus latisulcatus were investigated for 98 days. The specific growth rate (SGR) at 3.0% feed rate was significantly higher than at all higher feed rates, and there was no significant difference in SGR between 4.5%, 6% and 7.5%. Total ammonia nitrogen concentrations in all treatments remained low in the safe range for prawn culture. Dissolved inorganic nitrogen and nitrate nitrogen were significantly higher (P < 0.05) in prawn tanks received feed rates of 6.0% and 7.5%. Total phosphorus and the soluble reactive phosphorus linearly increased with the progression of the trial and feeding rates. Nutrient conversion rates were significantly higher (P < 0.05) in prawns receiving the feeding rate of 3.0% than feeding rates of 6.0% and 7.5%. The lowest food conversion ratio was recorded at feeding rates of 3% and 4.5%. Nutrient budget showed that 6.01–15.99% nitrogen and 4.53–9.29% phosphorus of the nutrient inputs were retained in the prawn biomass. The results indicated that the growth and nutrient conversion rate may not increase with the increase above 3.0% of biomass per day.     

Effect of food restriction on female reproductive performance in the redclaw crayfish Cherax quadricarinatus (Parastacidae,Decapoda)

Aquaculture activity has grown remarkably in the last years, crustaceans being the most profitable products because of their high prices. Feeding costs represent a large portion of total operating costs in the aquaculture industry. In this context, the objective of the present study was to evaluate the effect of food restriction on the reproductive performance of redclaw crayfish Cherax quadricarinatus. Females at the onset of sexual maturity were stocked with males and were fed daily a formulated diet at 1.5% (control group) and 0.5% (restricted group) of their mean weight. The experimental period lasted 105 days. The percentage of ovigerous females and broods successfully hatched tended to be higher in restricted females compared with control females, but egg volume and weight did not differ between both experimental groups. However, the lipid concentration of rematuring ovaries was lower in restricted females than control females, suggesting that food restriction affects the amount of reserves transferred to the ovaries during vitellogenesis. The nutritional state of females was independent of the amount of food provided, as reflected by similar growth parameters and biochemical composition of the hepatopancreas in control and restricted females. Based on these results, we conclude that it is possible to reduce the feeding rate of C. quadricarinatus females to one‐third of its original value without affecting their reproductive performance and somatic growth, at least for a 105‐day period. This finding provides a useful tool for commercial producers to decrease production costs and improve water quality in culture systems.     

Effects of feeding rate and frequency on growth performance,digestion and nutrients balances of Atlantic salmon (Salmo salar) in recirculating aquaculture systems (RAS)

A 10‐week study was conducted to investigate the effects of feeding rate and frequency on growth performance, digestion and nutrients balances of Atlantic salmon (Salmo salar) in replicated recirculating aquaculture systems (RAS). Replicated groups of juvenile salmon weighing 90 ± 2.5 g (mean ± SD) were fed a commercial feed (21.63 MJ kg^?1 gross energy) to designed feeding rate (1.4%, 1.6% and 1.8% body weight day^?1, BW day^?1) and feeding frequency (2 and 4 meals day^?1) combinations. Specific growth ratio varied between 1.15 ± 0.02 and 1.37 ± 0.16% day^?1, and feed conversion ratio ranged from 0.96 ± 0.03 to 1.16 ± 0.02. The nitrogen and phosphorus retention rates were from 36.50 ± 1.94 to 47.08 ± 5.23% and from 20.42 ± 1.05 to 38.59 ± 2.80%. Apparent digestibility coefficients (ADC) in dry matter, protein, lipid and energy showed no significant differences for all groups. However, fish fed at 1.6% BW day^?1 and 4 meal day^?1 groups had relatively better growth and nutrient retention efficiency compared to other groups. In addition, concentrations of nitrogenous and phosphorous compounds were also detected in this study. These results suggested that salmon of 100–200 g in RAS could in practice be fed at 1.6% BW day^?1 and 4 meals day^?1, taking environmental impacts into account.     

The effect of density in larval rearing of the pullet carpet shell Venerupis corrugata (Gmelin, 1791) in a recirculating aquaculture system

The pullet carpet shell Venerupis corrugata is an economically valuable species in several European countries, however, nowadays stocks are under high fishing pressure. Hatchery production of juveniles for release is a major contributor to strengthen the stock and consequently improve the sustainability of the natural stocks. This study aimed to determine the feasibility of rearing V. corrugata larvae with different larval densities (10, 40 and 200 larvae per mL) in a recirculating aquaculture system (RAS), compared with the traditional larval rearing methodology (Batch). The mean survival, growth and metamorphic rate of V. corrugata larvae in RAS was higher (11.1%; 71.3 μm; 21.6% respectively) than in the Batch system, in all tested densities. The larval growth was not affected by the initial density until 40 larvae per mL, however, 200 larvae per mL decreased the larval growth in length nearly 54 μm. The larval rearing time was shortened in 2 days in the RAS system. The physical, chemical and microbiologic parameters suggested that the tested densities were not excessive to disturb the biofilter stability of RAS. The V. corrugata larval rearing performed at high larval stocking densities in RAS system present a reduction in the operating costs to produce this species.     

The missing link: tidal‐influenced activity a likely candidate to close the migration triangle in brown shrimp Crangon crangon (Crustacea,Decapoda)

Life cycle closure for species inhabiting areas with daily varying currents but directed net water transport requires specific behavior to minimize losses due to advection of passive drifting life stages. Variations in swimming activity of different‐sized Crangon crangon (15–65 mm total length) were therefore monitored under constant laboratory conditions immediately after being caught in the German Wadden Sea. Activity of shrimps of different sizes, caught at different seasons, always peaked at times corresponding with ebb tide in the habitat from where they were taken. This behavior was maintained for several days if no external stimuli were present but shifted to night activity if a light–dark cycle was provided. The observed behavior/activity pattern was included in a coupled hydrodynamic and individual‐based model (IBM) and the shift in the location of a shrimp cohort was monitored over time. Performance of ebb tide activity not only allowed the shrimps to reach the preferred deeper winter and spawning areas but also allowed them to migrate against the dominating current from eastern nurseries to more western located spawning areas. Passively drifting larvae released at these locations and later larval and juvenile stages that perform flood tide transport can reach the nurseries again. This links the nurseries and adult spawning grounds and closes the migration triangle.     

Colonization history and human translocations explain the population genetic structure of the noble crayfish (Astacus astacus) in Fennoscandia: Implications for the management of a critically endangered species

1. The noble crayfish (Astacus astacus) is an endangered freshwater species in Europe. The main threat is from lethal crayfish plague, caused by the oomycete Aphanomyces astaci that has been spread over Europe by introduced North American crayfish species, acting as chronic carriers of the disease.
2. Most of the remaining noble crayfish populations are found in the Baltic Sea area, and there is an urgent need to implement conservation actions to slow down or halt the extinction rate in this region. However, limited knowledge about the genetic structure of populations in this area has so far precluded the development of conservation strategies that take genetic aspects into consideration.
3. Key objectives of this large-scale genetic study, covering 77 locations mainly from northern Europe, were to describe the contemporary population genetic structure of the noble crayfish in the Fennoscandian peninsula (Sweden, Norway, and Finland), taking postglacial colonization history into account, and to evaluate how human activities such as stocking have affected the genetic structure of the populations.
4. Analyses of 15 microsatellite markers revealed three main genetic clusters corresponding to populations in northern, middle, and southern Fennoscandia, with measures of genetic diversity being markedly higher within populations in the southern cluster. The observed genetic structure probably mirrors two main colonizations of the Baltic Sea basin after the last glaciation period. At the same time, several deviations from this pattern were observed, reflecting past human translocations of noble crayfish.
5. The results are discussed in relation to the conservation and management of this critically endangered species. In particular, we recommend increased efforts to protect the few remaining noble crayfish populations in southern Fennoscandia and the use of genetic information when planning stocking activities, such as reintroductions following local extinctions.

     

Direct visualization of the novel pathogen,Spiroplasma eriocheiris,in the freshwater crayfish Procambarus clarkii (Girard) using fluorescence in situ hybridization

Spiroplasma eriocheiris is the first spiroplasma strain known to be pathogenic to freshwater crustaceans. It has caused considerable economic losses both in the freshwater crayfish Procambarus clarkii (Girard) and in some other crustaceans. The monitoring of the pathogen in crustacean populations and study of its behaviour in the laboratory require the development of reliable diagnostic tools. In this article, we improved microscopic identification of S. eriocheiris by combining in situ hybridization with specific fluorescently labelled oligonucleotide probes. The established fluorescence in situ hybridization (FISH) allowed simultaneous visualization, identification and localization of S. eriocheiris in the tissues of diseased crayfish P. clarkii and exhibited low background autofluorescence and ideal signal‐to‐noise ratio. With the advantages of better tissue penetration, potentially more specific and stable, we designed three species‐specific oligonucleotide probes utilizing the sequences of 16S‐23S rRNA intergenic spacer regions (ISRs) of S. eriocheiris. Positive hybridization signals were visualized in haemocytes and connective tissues of hepatopancreas, cardiac muscle and gill from diseased crayfish. This unique distribution pattern matched the pathological changes when diagnosed by H&E staining and indicated that S. eriocheiris probably spread throughout the tissues in P. clarkii by hemokinesis. This assay will facilitate our understanding of the pathogenesis of S. eriocheiris and enhance the early diagnosis of the novel pathogen.     

The use of acoustic acceleration transmitter tags for monitoring of Atlantic salmon swimming activity in recirculating aquaculture systems (RAS)

Successful operation of recirculating aquaculture systems is dependent on frequent monitoring of the optimal function of water treatment processes in order to maintain environmental conditions for optimal growth and welfare of the fish. Real time monitoring of fish status is however usually not an integrated part of automatized systems within RAS. The aim of this study was to evaluate the use of implanted acoustic acceleration transmitters to monitor Atlantic salmon swimming activity. Twelve salmon post-smolts were individually tagged and distributed in three tanks containing salmon at start density of 50 kg m⁻³. The tagging did not cause any mortality and all individuals increased their body weight during this study. Following initial recovery, acceleration data were continuously logged for one month, including treatment periods with exposure to hyperoxic (170% O₂ saturation) and hypoxic (60% O₂ saturation) conditions, and different tank hydraulic retention times (HRT; 23 and 58 min). Changes in-tank dissolved oxygen levels to hyperoxic and hypoxic conditions reduced the total activity of Atlantic salmon in this study. On the contrary, increased and reduced tank HRT increased the total activity levels. Feeding periods induced a sharp increase in the Atlantic salmon swimming activity, while irregular feeding caused larger oscillations in activity and also lead to increased swimming activity of the tagged fish. Atlantic salmon responded with a maximum recorded total activity to stress caused by technical problems within the system and consequent changes in the RAS environment. The results of this study indicate that Atlantic salmon respond quickly with changed swimming activity to changes in the water quality and acute stress caused by normal management routines within RAS. The use of acoustic acceleration transmitters for real time monitoring of swimming activity within aquaculture production systems may allow for rapid detection of changes in species-specific behavioural welfare indicators and assist in the refinement of best management practices. In addition, acceleration tag could potentially serve as a valuable research tool for behavioural studies, studies on stress and welfare and could allow for better understanding of interaction between fish and RAS environment.