Zooplankton and epibenthic fauna in shrimp ponds: factors influencing assemblage dynamics

The assemblage composition, biomass and dynamics of zooplankton and epibenthos were examined in a commercial shrimp (penaeid prawn) pond in subtropical Australia. Physicochemical characteristics of the pond water were measured concurrently. Numbers and biomass of zooplankton in the surface tows (140 μm mesh) varied from 111.7 ind. L^?1 (324 μg L^?1) to 8.3 ind. L^?1 (44.2 μg L^?1). Immediately after the ponds were stocked with shrimp postlarvae there was a rapid decline in zooplankton numbers, particularly the dominant larger copepods. We attributed this to predation by the shrimp postlarvae. Subsequent peaks in zooplankton numbers were principally due to barnacle nauplii. Changes in abundance and biomass of the zooplankton assemblage were not correlated with physicochemical characteristics. Epibenthic faunal abundance in the beam trawls (1 mm mesh) peaked at 14 ind. m^?2 and the biomass at 0.8 g m^?2. Unlike zooplankton, the peaks in abundance of epibenthos did not correspond to the peaks in biomass. This was due to the large differences in the size of the dominant taxa across the season. Sergestids (Acetes sibogae) and amphipods were the most abundant taxa in beam trawl samples, with amphipods abundance increasing towards the end of the growout. Negative correlations were found between epibenthos abundance and pH and temperature. These relationships were strongly influenced by the high abundances of amphipods and may reflect an effect on the growth of macroalgae in the pond rather than a direct effect on the epibenthos. No correlations were found between epibenthic fauna biomass and physicochemical parameters. Abundances of epibenthic fauna were not related to zooplankton densities, indicating that this source of food was not likely to be a limiting factor. Neither the pond water exchange regime nor moon phase could explain changes in abundances of zooplankton or epibenthos assemblages. Zooplankton clearly contribute to the nutrition of shrimp postlarvae immediately after stocking. The establishment of an abundant assemblage of zooplankton before stocking shrimp postlarvae would appear to be beneficial, if not essential. Later in the season, zooplankton and epibenthos apparently contribute little to shrimp biomass. Owing to their relatively low biomass, the consumption of shrimp feeds by epibenthos is likely to be insignificant compared with that of the shrimp.     

Effects of water exchange and abiotic factors on zooplankton and epibenthic fauna in shrimp ponds

Assemblages of zooplankton and epibenthic invertebrates were collected from a commercial Penaeus monodon (Fabricius) pond at fortnightly intervals over an entire grow‐out season. The pond inlet and outlet water were also sampled intensively over three 1‐week periods throughout the season. Before stocking the ponds with shrimp postlarvae, copepods dominated the zooplankton. Immediately after the ponds were stocked, there was a rapid decline in zooplankton numbers, particularly the dominant larger copepods, suggesting heavy predation by shrimp postlarvae. For the rest of the season, barnacle nauplii were the dominant zooplankton component in the pond. Pond water exchanges had little detectable influence on the composition or density of the zooplankton assemblage. Instead, the dominance of barnacle nauplii appeared to have been maintained by steady recruitment due to barnacle reproduction in the pond. While changes in the biomass of pond zooplankton were not correlated with physico‐chemical characteristics, changes in density were positively correlated with temperature, and negatively correlated with pH, dissolved oxygen and secchi disc readings. Epibenthic faunal density peaked at the end of the season, while the biomass peaked during the middle part of the season. Sergestids (Acetes sibogae Hansen) were the most abundant epibenthic taxa. No correlations were found between physico‐chemical parameters and epibenthic fauna biomass or density. Abundances of epibenthic fauna were not related to zooplankton densities, suggesting that trophic interactions between these assemblages is not important. No Acetes were captured in samples of outlet water, and only on a single occasion were large numbers captured in the inlet water; after this, there was a notable increase in the number of Acetes in the pond. This evidence, together with the lack of an increase in the size of Acetes during the season, suggests that water exchange is an important but unpredictable source of recruitment of epibenthic fauna into the pond. The results emphasize the benefits of ensuring that appropriate zooplankton assemblages have been introduced into the ponds, when they are filled, to support the shrimp immediately after stocking. This will depend on the initial inoculum and may be difficult to manipulate with water exchanges once established. Assemblages of epibenthic fauna appear more likely to change with exchanges and may need to be monitored across the season, particularly if their presence reduces production through adverse impacts such as competition with postlarvae, introduction of disease or deteriorated water quality.     

Study of zooplankton communities in shrimp earthen ponds, with and without organic nutrient-enriched substrates

Zooplankton communities were studied in shrimp ponds using different strategies to enhance natural productivity. The traditional treatment consisted of performing the strategy of simple fertilization (TT); for the alternative treatment (AT), fertilization was combined with the use of organic substrates enriched with nutrients; both treatments were stocked with shrimp post-larvae (Litopenaeus vannamei). Additionally, ponds with substrates but without shrimp were also studied (C). Total zooplankton concentration was greater in C ponds (1,002 org L^?1) followed by AT (309 org L^?1) and TT (124 org L^?1), respectively. Copepods were the most abundant organisms in all treatments (≥65 %), but their concentration decreased when shrimp were present in ponds. Such decline of copepods enhanced the proliferation of other zooplankton organisms such as polychaetes, protozoans, barnacles, ciliatea and others. Contents of shrimp stomachs exhibited a shrimp preference for copepods, polychaetes and protozoans; in addition, stomach contents of shrimp revealed their higher consumption of zooplankton when these organisms are abundant in the culture. Finally, shrimp reared in AT had a better growth performance than those from TT. It is concluded that enriched substrates are useful to improve and maintain high concentrations of zooplankton; copepods seem to suppress the proliferation of other zooplankton populations; however, they are preferred preys by shrimp.     

Growth and performance of Penaeus semisulcatus (de Haan) fed with two commercial shrimp feeds

Two feeding trials were conducted in two stages to compare growth and performance, grow‐out (1–9 g b.w.) and fattening (13–19 g b.w.), of Penaeus semisulcatus. Shrimps were fed with two commercial feeds: P. monodon feed and P. japonicus feed. Both experiments were conducted using an indoor flow‐through tank culture system. The results reveal that the growth performance of shrimp fed with P. japonicus feeds (0.91 g shrimp^?1 week^?1) for the grow‐out stage was significantly better than shrimp fed with P. monodon feeds (0.63 g shrimp^?1 week^?1). The growth performance of shrimp fed with P. monodon feed (0.56 g shrimp^?1 week^?1) for the fattening stage was significantly better than shrimp fed with P. japonicus feed (0.42 g shrimp^?1 week^?1). The feed conversion ratios of both diets for the two sizes did not differ significantly. Thus, it is recommended that P. japonicus feeds be fed to P. semisulcatus during the grow‐out stage. During the fattening stage, the better growth performance of the shrimp fed with P. monodon feed makes it a better feed. However, colour and overall acceptability of shrimp fed with P. japonicus feed were generally higher than those fed with P. monodon feed.     

Toxicity of the aquaculture pesticide cypermethrin to planktonic marine copepods

The acute and sublethal toxicity of cypermethrin, the active ingredient in the sea lice treatment formulation Excis^®, to non‐target planktonic marine copepods was determined. The comparative sensitivities of three life stages (nauplii, copepodites, adults) of four common marine copepods (Acartia clausi, Pseudocalanus elongatus, Temora longicornis and Oithona similis) were assessed in 48‐h exposures, followed by a recovery period in toxicant‐free sea water. The cyclopoid copepod, O. similis, was most affected by cypermethrin, with EC₅₀ values ranging from 0.14 to 0.24 μg L^?1 for nauplii and adults respectively. With the exception of T. longicornis nauplii, the calanoid copepods (A. clausi, P. elongatus and T. longicornis) responded similarly to cypermethrin. Overall, 48‐h EC₅₀ values ranged from 0.12 μg L^?1 (T. longicornis nauplii) to >5 μg L^?1 (P. elongatus adults). For all species, nauplii and copepodite EC₅₀ values were lower than those of the adults. The primary toxic effect, immobilization, was generally irreversible. A sublethal test with adult A. clausi females, involving pulse exposures over 4 days measured a significant increase in egg production at the higher concentrations (1.58 and 5 μg L^?1). Concentrations causing acute toxicity to planktonic copepods were lower than the recommended sea lice treatment concentration of 5 μg L^?1 cypermethrin, indicating the potential for toxic effects in the field. However, acute toxicity values were higher than the Environmental Quality Standard of 0.016 μg L^?1 for dispersing treatment plumes, suggesting that cypermethrin released to the marine environment following sea lice treatments is unlikely to affect adversely planktonic copepods.     

Production of Tiger Shrimp (Penaeus monodon) in Potassium Supplemented Inland Saline Sub-Surface Water

Abstract

Potassium deficient inland saline (10 g L^?1 salinity) well water was supplemented with muriate of potash to achieve 50% (57 mg L^?1) and 100% (114 mg L^?1) of seawater potassium concentration and used for the production of tiger shrimp (Penaeus monodon). Total mortality was observed in non-supplemented water within 6 days compared to 88.0% survival in K⁺100% and 85.3% survival in K⁺50% up to 60 days. P. monodon were subsequently cultured for 110 days in two identical 0.25-ha ponds supplied with water of 10 g L^?1 and supplemented with the potassium equivalent of 35% of seawater. Survival and production were 55.8% to 64.25% and 157.70 kg (630.8 kg ha^?1) to 172.75 kg (691 kg ha^?1), respectively.     

Are egg production and respiration of the marine pelagic copepod Acartia steueri influenced by crowding?

The understanding of the biological responses of copepods under crowding conditions contributes to establish their stable cultures at high densities for aquaculture industry, which are preferred live feeds for fish larvae. The present study investigated survivorship, fecundity, hatching success and respiration rate, of Acartia steueri raised under five densities, from 100 to 2,000 ind. L^?1, to clarify the biological responses of the copepod under dense culture. There were no significant differences in survival, fecundity and hatching success among all density conditions, whereas the respiration rate at 2,000 ind. L^?1 decreased by 80% as compared with a condition at 100 ind. L^?1. The female copepods raised under a copepod density of >500 ind. L^?1 probably invested a larger proportion of energy in reproduction in relation to total assimilated energy as compared with females under lower copepod densities. This change of energy allocation may allow A. steueri under high densities to maintain high fecundity. Acartia steueri might be a promising species for dense culture because its mortality and fecundity were independent of the effect of crowding, and the density‐dependent reduction in the metabolic rate might increase reproductive investment to maintain a constant rate of reproduction even under high densities.     

Inorganic nitrogen addition in a semi‐intensive turbot larval aquaculture system: effects on phytoplankton and zooplankton composition

A nitrogen manipulation experiment was conducted in a semi‐intensive outdoor system where turbot larvae feed on copepods. Nitrogen addition is hypothesized to stimulate a cascade reaction increasing phytoplankton biomass, copepods’ productivity and larval fish survival. Triplicates were established for three treatments: a control with no additional nitrogen, a pulsed dose where nitrogen was added in three doses over time and a full dose where all nitrogen, equal to the total of the pulse dose treatment, was added initially. In the control, chlorophyll a averaged 3.3 ± 1.5 μg L^?1 and phytoplankton was dominated by diatoms, while the pulsed and full dose treatments showed chlorophyll a at 28.6 ± 9.9 and 47.7 ± 10.0 μg L^?1, respectively, with dinoflagellates as the main phytoplankton group. Due to photosynthesis, pH increased >9 in both the nitrogen treatments compared to the control (8.5). Potential toxic dinoflagellates, including Alexandrium pseudogonyaulax and Prorocentrum spp., became dominant in the nitrogen treatments and might have arrested zooplankton recruitment. Laboratory experiments with a toxic strain of A. pseudogonyaulax proved that Acartia tonsa reproduction and naupliar survival were affected negatively at realistic fish tank concentrations of 100 and 20 cells mL^?1, respectively. Compared to the control, pulsed and full dose treatments reached higher copepod biomass and showed a shift over time in species composition from Centropages hamatus to Acartia spp. However, high pH levels and dinoflagellate blooms had a negative effect on larval fish survival, suggesting management improvements on water quality and separation between copepods and fish production tanks.     

Low-density silver carp Hypophthalmichthys molitrix (Valenciennes) polyculture does not prevent cyanobacterial off-flavours in channel catfish Ictalurus punctatus (Rafinesque)

Silver carp Hypophthalmichthys molitrix (Valenciennes) were co‐cultured with channel catfish Ictalurus punctatus (Rafinesque) in 0.4 ha earthen ponds to determine the impacts of carp grazing on pond phytoplankton communities and cyanobacterial off‐flavours in catfish. Carp were stocked at densities of 0, 75, or 250 fish ha^?1 in seven replicate ponds per treatment. The mean chlorophyll a concentrations (a measure of phytoplankton standing crop) steadily increased in all treatments from about 100 μg L^?1 in April to more than 400 μg L^?1 by mid‐October. Silver carp had no affect (P>0.1) on chlorophyll a concentrations across all sampling dates (April though October) or for sampling dates late in the growing season (August–October) when the prevalence of cyanobacterial off‐flavours among catfish populations is usually greatest. Silver carp did not eliminate odour‐producing cyanobacteria from pond phytoplankton communities: on sampling dates in September and October, three to six ponds in all treatments contained populations of the odour‐producing cyanobacteria Oscillatoria perornata, Anabaena spp., or both. Failure of silver carp to eliminate odour‐producing cyanobacteria resulted in a relatively high incidence in all treatments of ponds with off‐flavoured catfish. On sampling dates in September and October, catfish in three to five ponds in each treatment were tainted with either musty (2‐methylisoborneol) or earthy (geosmin) off‐flavours. The presence of silver carp had no obvious effect on off‐flavour intensity: on each sampling date, at least three ponds in each treatment contained catfish described as distinctly to extremely off‐flavored. Apparently, hypertrophic conditions in catfish ponds overwhelm the effect of silver carp grazing at the low carp densities used in this study.     

Effects of crushed conspecifics on growth and survival of Penaeus monodon Fabricius post larvae

In the present study, the hypothesis tested was that Penaeus monodon post‐larvae (PL) experience lower growth when exposed to crushed conspecifics, which was achieved by exposing individual P. monodon PL with abundant food for 4 weeks to a gradient from 0 to 100 crushed conspecific PL L^?1. Both dry weight (48.5±7.2 mg) and body size (28.0±1.3 mm) of animals exposed to 1 macerated PL L^?1 were significantly (P≤0.011) higher than those of animals in treatments with 0, 5 and 10 crushed PL L^?1 (average over treatments: 25.6±3.2 mg; 23.4±0.5 mm). All animals died within 1 week when exposed to 70 and 100 crushed PL L^?1, and within 3–4 weeks when exposed to 50 and 30 crushed PL L^?1. Exposure time affected mortality and it appeared that LC₅₀ values decreased from 60 to 13 crushed PL L^?1 from 1 to 4 weeks' exposure. Survival of P. monodon PL was negatively correlated to pH, biological oxygen demand, ammonia and nitrate. In conclusion, low dose of crushed conspecifics has a stimulatory effect on P. monodon PL, as larvae were heavier and larger, while high doses cause high mortality.     

Nursery rearing of the Asian catfish, Clarias macrocephalus (Günther), at different stocking densities in cages suspended in tanks and ponds

Growth and survival of hatchery‐bred Asian catfish, Clarias macrocephalus (Günther), fry reared at different stocking densities in net cages suspended in tanks and ponds were measured. The stocking densities used were 285, 571 and 1143 fry m^?3 in tanks and 114, 228 and 457 fry m^?3 in ponds. Fish were fed a formulated diet throughout the 28‐day rearing period. Generally, fish reared in cages in ponds grew faster, with a specific growth rate (SGR) range of 10.3–14.6% day^?1, than those in cages suspended in tanks (SGR range 9–11.3% day^?1). This could be attributed to the presence of natural zooplankton (copepods and cladocerans) in the pond throughout the culture period, which served as additional food sources for catfish juveniles. In both scenarios, the fish reared at lower densities had significantly higher SGR than fish reared at higher densities. In the pond, the SGR of fish held at 228 and 457 m^?3 were similar to each other but were significantly lower than those of fish held at 114 m^?3. The zooplankton in ponds consisted mostly of copepods and cladocerans, in contrast to tanks, in which rotifers were more predominant. Per cent survival ranged from 85% to 89% in tanks and from 78% to 87% in ponds and did not differ significantly among stocking densities and between rearing systems. In conclusion, catfish nursery in cages suspended in tanks and ponds is density dependent. Catfish fry reared at 285 m^?3 in tanks and at 114 m^?3 in ponds had significantly faster growth rates than fish reared at higher densities. However, the desired fingerling size of 3–4 cm total length for stocking in grow‐out culture can still be attained at stocking densities of 457 m^?3 in nursery pond and 571 m^?3 in tanks.     

Toxicity of chlorine to different sizes of black tiger shrimp (Penaeus monodon) in low-salinity shrimp pond water

An experiment was conducted, in a dark room with controlled temperature (27.3–28.4 °C), to determine the acute toxicity of chlorine concentration to black tiger shrimp (Penaeus monodon fabicus) of sizes 0.02 g, 2.75 g, 8.47 g and 23.65 g. Toxicity tests on each of these shrimp sizes were run in triplicate in glass jars under static conditions without media renewal. The concentration of active chlorine that killed 50% of the shrimp of each size after 24‐h exposure (LC₅₀‐24 h) was used as an indicator of acute toxicity. Chlorine concentrations applied in the shrimp toxicity test ranged from 2.0 to 14.5 mg L^?1 in shrimp pond water. As the test water contained total suspended solids of 22.0–85.0 mg L^?1 and total ammonia nitrogen of 0.18–0.40 mg L^?1, the resultant concentrations of combined residual chlorine ranged from 0.6 to 3.5 mg L^?1, which were the effective doses causing shrimp mortality. The test results showed that 24‐h LC₅₀ for average shrimp size at 0.02, 2.75, 8.47 and 23.65 g occurred in water containing combined residual chlorine at a concentration of 0.91, 1.39, 1.74 and 1.98 mg L^?1, for which the original application doses were 6.96, 2.05 11.50 and 13.34 mg L^?1 respectively.     

Biological characteristics of the improved extensive shrimp system in the Mekong delta of Vietnam

Low and unstable shrimp yields of the improved extensive shrimp system has been a tremendous obstacle for economic development in the coastal areas of Southern Vietnam. To investigate the biological characteristics of this system, ponds in the coastal Cai Nuoc district, Mekong delta of Vietnam, were monitored. Results showed that the system was not optimal for shrimp. While chlorophyll a (chl a) (1.51–37.2 μg L^?1), phytoplankton density (6333–974 444 cells L^?1) and zooplankton density (7.1–517.2 ind L^?1) were abundant and comparable to shrimp farms elsewhere, zoobenthic community was very poor (7–1971 ind m^?2). Toxin‐producing cyanobacteria (Oscillatoria limosa, Oscillatoria formosa, Anabaena sp. and Phormidium tenue) were found. Total bacteria and Vibrios were present in large numbers (respectively 1.04 × 10⁵ and 6.64 × 10² CFU mL^?1 in pond water, 6.33 × 10⁵ and 9.47 × 10³ CFU g^?1 in sediment). Presence of toxin‐producing organisms, poor zoobenthic community and abundance of Vibrios all can enhance shrimp susceptibility to diseases. The following measures are recommended to improve the situation: (1) complete testing of seeds for pathogens, (2) not to incorporate fish into shrimp ponds and (3) applying no‐culture breaks and pathogen‐killing chemicals.     

Response of biota to aeration rate in low water exchange ponds farming white shrimp, Penaeus vannamei Boone

The response of phytoplankton, zooplankton and benthos to four aeration rates was evaluated in ponds farming white shrimp, Penaeus vannamei Boone, with less than 5% water exchange. Phytoplankton biomass (measured as chlorophyll-fl) was higher in ponds with aeration rates of 0 and 6 h day^?1 than in those with rates of 24 hday^?1. The abundance of zooplankton and benthos (organisms m^?2) were higher in ponds with aeration rates of 0 and 6 h day^?1, and lower in ponds with rates of 12 and 24 h day^?1. The nauplii of different crustaceans, copepods and larval polychaetes were the most abundant organisms of the zooplankton community. Differences in zooplankton composition were observed among treatments. Polychaetes were the most abundant benthic organisms during the culture period. These organisms were more abundant in ponds with lower aeration rates. The guts of shrimp from ponds with aeration rates of 0 and 6 h day^?1 had a higher abundance of zooplankton and benthic organisms than those from the other treatments. That abundance decreased over time in all treatments. Shrimp had better growth in ponds with an aeration of 6 hday^?1. Survival and yield were similar in ponds with aeration rates of 6, 12 and 24 h day^?1, and lower in ponds with rates of 0 h day^?1.     

Effect of promoted natural feed on the production,nutritional, and immunological parameters of Litopenaeus vannamei (Boone, 1931) semi‐intensively farmed

The effect of promoted biota on the production parameters, water quality, nutritional and immunological condition of Litopenaeus vannamei was assessed in semi‐intensive ponds. Earthen ponds were used as experimental units: three with formulated + natural promoted feed + shrimp (T1), three with formulated feed + shrimp (T2), and three with promoted natural feed without shrimp (Control). The dissolved oxygen (DO) levels were optimal for all treatments (≥6 mg L^?1) as well as the pH (8.4–8.6). Total ammonia nitrogen was greater in T2 (0.10 mg L^?1) than T1 (0.07 mg L^?1) and the Control (0.06 mg L^?1). Phytoplankton, zooplankton and benthos were more abundant in T1 and the Control. The promotion of natural feed had a positive effect on all the production parameters of shrimp with an increase of 19.0%, 3.5% and 23.9% in weight gain, survival, and final biomass, respectively; also it was observed a decrease of 13.9% in feed conversion ratio. No differences in haemolymph parameters were observed for nutritional indicators (glucose, cholesterol, proteins, and triglycerides) nor for immunological response (phenoloxidase and prophenoloxidase). The results indicate that the promotion of biotic communities enhances the production parameters of farmed shrimp, without affecting the nutritional and immunological status. Also the water quality was improved by the presence of biota.     

Pharmacokinetics of oxolinic acid in black tiger shrimp, Penaeus monodon Fabricius, and the effect of cooking on residues

This study examined the pharmacokinetics and bioavailability of oxolinic acid (OA) in black tiger shrimp Penaeus monodon Fabricius, in brackish water (salinity 10 g L^?1) at 28–29°C, after intra‐sinus (10 mg kg^?1) and oral (50 mg kg^?1) administration and also investigated the net changes of OA residues in the shrimp after cooking (boiling, baking and frying). The haemolymph concentrations of OA after intra‐sinus dosing were best described by a two‐compartment open model. The distribution and elimination half‐lives were 0.84 and 17.7 h respectively. The apparent volume of distribution at a steady state and the total body clearance were estimated to be 2061 mL kg^?1 and 90.1 mL kg^?1 h^?1 respectively. The bioavailability of OA after an oral administration was 7.9%. The peak haemolymph concentration, the time to peak haemolymph concentration and the elimination half‐life after oral administration were 4.20 μg mL^?1, 4 h and 19.8 h respectively. Oxolinic acid muscle and shell levels increased to a maximum (muscle 1.76 μg g^?1 and shell 8.17 μg g^?1) at 4 h post administration and then decreased with the elimination half‐life value of 20.2 and 21.9 h respectively. Residual OA in muscle and shell was reduced by 20–30% by each cooking procedure examined.     

Feeding,egg production and laboratory culture of Schmackeria poplesia Shen (Copepoda: Calanoida)

Copepods are candidates with great potential as live prey for rearing fish larvae and juveniles in aquaculture; however, the techniques for a large‐scale culture of copepods are yet to be developed. In this study, we examined the effects of water temperature, salinity, prey concentration and algal species on the grazing and egg production rates of a calanoid copepod Schmackeria poplesia (Copepoda: Calanoida). The results showed that the grazing rate of S. poplesia was the highest when the copepods were cultured in seawater with temperature of 25 °C, salinity of 20 g L^?1, prey concentration at 10⁵ cells mL^?1 and supplied with Platymonas helgolandica as the prey. The egg production rates, however, was the highest when copepods were fed with a mixed prey of Isochrysis galbana and Phaeodactylum tricornutum (cell ratio 1:1, prey concentration 10⁵ cells mL^?1) at 25 °C, 20 g L^?1 of salinity. A 100 L cultural system was established to culture S. poplesia under the condition optimized for egg production. The total number of copepods increased 40–43‐fold with the production rates of 87–290 copepods L^?1 day^?1 in 14 days. This research was the first attempt for a large‐scale culture of S. poplesia and the technique established can be further applied in aquaculture.     

Bacteria in shrimp pond sediments: their role in mineralizing nutrients and some suggested sampling strategies

Strategies for sampling sediment bacteria were examined in intensive shrimp. Penaeus monodon (Fabririus), ponds in tropical Australia. Stratified sampling of bacteria at the end of the production season showed that the pond centre, containing flocculated sludge, had significantly higher bacterial counts (15.5 × 10⁹ g-¹ dw) than the pond periphery (8.1 × 10⁹g^?1 dw), where the action of aerators had swept the pond floor. The variation in bacterial counts between these two zones within a pond was higher than that between sites within each zone or between ponds. Therefore, sampling effort should be focused within these zones; for example, sampling two ponds at six locations within each of the two zones resulted in a coefficient of variation of ± 5%. Bacterial numbers in the sediment were highly correlated with sediment grain size, probably because eroded soil particles and organic waste both accumulated in the centre of the pond. Despite high inputs of organic matter added to the ponds, principally as pelleted feeds, the mean bacterial numbers and nutrient concentrations (i.e. organic carbon, nitrogen and phosphorus) in the sediment were similar to those found in mangrove sediments. This suggests that bacteria are rapidly remineralizing particulates into soluble compounds. Bacterial numbers were highly correlated with organic carbon and total kjeldahl nitrogen in the sediment, suggesting that these were limiting factors to bacterial growth.     

Dietary astaxanthin levels affect colour,growth, carotenoid digestibility and the accumulation of specific carotenoid esters in the Giant Tiger Shrimp,Penaeus monodon

The carotenoid astaxanthin (Axn) plays a vital role in shrimp pigmentation, with direct influence on product quality, and forms a significant cost component of shrimp aquaculture feeds. However, the effects of dietary Axn on other measures of shrimp physiological performance are varied, and the efficiency of carotenoid uptake from the diet and deposition in shrimp tissues is poorly defined. This study fed juvenile shrimp (Penaeus monodon) diets that contained 0, 25, 50 or 100 mg kg^?1 Axn for 6 weeks. Shrimp fed carotenoid‐free diets had significantly reduced colour and growth than those fed carotenoids, but survival was unaffected. Carotenoid digestibility improved as dietary carotenoid levels increased, and was 98.5% in shrimp fed 100 mg kg^?1 Axn. After 6 weeks, whole body carotenoid levels were significantly depleted in 0 or 25 mg kg^?1 fed shrimp, compared with those fed 50 or 100 mg kg^?1 or compared with initial shrimp. This study also showed that Axn monoesters were enriched with saturated fatty acids, whereas Axn diesters were enriched with monounsaturated and polyunsaturated fatty acids. Combined, these studies demonstrate that a total dietary carotenoid intake of between 25 and 50 mg kg^?1 Axn is required for normal shrimp growth and health in P. monodon. Evidence suggests that there is a functional role for the accumulation of carotenoids and the formation of specific Axn fatty acid esters, and these may be linked to the metabolism, storage, mobilization or deposition of Axn within various tissues.     

Administration of hot‐water extract of Padina boergesenii via immersion route to enhance haemolymph‐immune responses of Fenneropenaeus indicus (Edwards)

Various polysaccharides extract from marine algae to increase the non‐specific immune system in crustacean. In this study, effects of hot‐water extract on total haemocyte count, total plasma protein, Phagocytic activity, bacterial clearance efficiency and bactericidal activity while the shrimp Fenneropenaeus indicus (10.12±2.18 g) were immersed in seawater (40 g L^?1 and 25±0.8 °C) containing hot‐water extract of brown algae Padina boergesenii at 100, 300 and 500 mg L^?1 for 1–4 h, were investigated. These parameters increased significantly (P<0.05) when the shrimp were immersed in seawater containing hot‐water extract at 100 mg L^?1 after 3 h and 300 and 500 mg L^?1 after 2 h. Fenneropenaeus indicus that were immersed in hot‐water extract at 300 and 500 mg L^?1 had significantly increased phagocytic activity and increased clearance efficiency to Vibrio harveyi after 2 h. But bactericidal activity increased after 1 h immersed in 500 mg L^?1 concentration.