Opto-electronic counters for juveniles of macrobrachium rosenbergii (de Man): Supporting equipment and use of counter B under commercial hatchery conditions

To count postlarvae or juveniles of M. rosenbergii with the high speed opto-electronic Counter B, a clean water supply, a system for delivery of juveniles into the counting device, the collection of counted juveniles and partition of these into containers for delivery to ponds, are required. Juveniles are collected from rearing tanks without contamination by particles of detritus, which would otherwise be counted. The infrastructure, counter performance, juvenile handling procedures and survival tests done on machine-counted juveniles are described. Counting speed (juveniles per hour), counting errors and labour needs (men) are: 200 000, <1% and two for machine counting; 10 000, >2% and six for hand counting; a supervisor is required in both cases. Survival of machine-counted juveniles is the same as that of hand counted ones, indicating that the electronic counter and methods of using it have no adverse effects on juvenile prawns of this species. It is believed that this counter is unique, and that it has wide applicability to counting various aquatic organisms.     

Shelter colour preference of the postlarvae of the giant freshwater prawn <Emphasis Type="Italic">Macrobrachium rosenbergii</Emphasis>

The addition of artificial shelters of various materials has been used in Macrobrachium rosenbergii tanks and ponds as a means of increasing productivity. The present study investigated the shelter colour preference of M. rosenbergii postlarvae (age 15–18 days after metamorphosis) in the laboratory. Shelter occupancy tests were performed on four groups of 200 postlarvae in four 57-l aquaria, into which were placed shelters made of rigid coloured netting sewn into four-layered cubes open on two sides. The shelters were presented in six colour pairs: black vs dark green, black vs light green, black vs blue, dark green vs light green, dark green vs blue, and light green vs blue. Colour preference was tested six times for each colour pair. The data obtained were analyzed using Thurstone’s law of comparative judgment. The mean z-score was significantly highest (i.e., highest preference) for the black shelter. Vision was involved in the detection of and approach to the shelter. When released in aquaria, intact-eyed individual postlarvae directly approached the shelter straight away, whereas blind postlarvae (paint over the eyes) swam around randomly and occupied the shelter only after accidental contact much later. Postlarvae in open water out of the shelter exhibited frequent aggressive contact, while those in the shelter were quiescent. The use of black shelters in rearing tanks is thus recommended for reducing stress and aggression among M. rosenbergii postlarvae in the hatchery.     

Opto-electronic counters for postlarvae and juveniles of Macrobrachium rosenbergii (de Man); design and tests of Type B counter

The disadvantages of hand counting hatchery produced juveniles of Macrobrachium rosenbergii have been overcome by development of a high speed opto-electronic counter. The hydraulic, mechanical and electronic designs of the Type B counter are described. The counter, extremely fast in principle, is being used and tested under commercial hatchery conditions. Its practical speed of operation and accuracy are expected to exceed 100 000 juveniles per hour and 95%, respectively.About 80% of juveniles show some morphological damage but most of this probably originates in the hatchery rearing tanks. Tests show that slight additional damage is caused only to the antennules of juveniles passing through the counter but this does not affect their subsequent growth rate and survival. It is suggested that density dependent aggression in hatchery tanks is the principal cause of damage. Counter B is shown to be suitable and safe for counting freshwater prawn juveniles. This counter could be adapted to count other macroscopic aquatic organisms via suitable dimensional scaling. No other counters of this type and purpose appear to exist.     

Stocking Density for Nursery Production of Redclaw Crayfish,Cherax quadricarinatus,in a Recirculating System

Redclaw crayfish, Cherax quadricarinatus, early juveniles were reared at different stocking densities in a closed recirculation system using 12-L plastic containers as rearing tanks. Initial stocking densities were 1.0, 1.5, 2.0, 2.5, and 3.0 per liter (66, 89, 111, 133, and 156 crayfish/m², respectively). Rearing period was 42 days. Each density was tested with five replicates. Shelter (0.112 m²) was added to double the surface area of rearing tanks. Animals were fed ad libitum twice a day with a commercial diet containing 35% crude protein. There were no significant differences (P < 0.05) in length and specific growth rate (SGR) among stocking densities. Final weight and daily weight gain, however, were significantly higher at the density of 66 per m² (1.0 per liter). Total biomass at harvest increased with density. Survival was affected by stocking density from day 28 onward, decreasing with density from 62.7 ± 7.6% obtained at 66 crayfish/m² to 44.85 ± 8.18% at 156 crayfish/m².     

Research on intensive aquaculture: Proceedings of a German-Israeli seminar on aquaculture held from March 10 to 11, 1980 at Shefayim,Israel. H. Rosenthal and O.H. Oren (Editors). European Mariculture Society,Belgium, Special Publication No. 6, 1981. ii + 277 pp., BFr. 1150

A solar-heated greenhouse containing recirculating fish production systems was used to culture Tilapia nilotica and T. aurea. Fish production was maximized by sequential rearing, grading, and restocking of fish at high densities to utilize each system fully. Marketable-size (167 g) fish were produced from 29-g fingerlings in 137 days. No reproduction was recorded.Spawning in February was induced naturally by a $\text{16}\text{L}\text{8}\text{D}$ photoperiod, water temperature of 24°C, and reducing stock density.     

Laboratory rearing of Loligo opalescens, the market squid of California

The squid Loligo opalescens (Cephalopoda, Mollusca) was reared in artificial sea water in a closed system consisting of two 1300-l circular tanks. When the squids reached mantle lengths of 20 to 30 mm, they were transferred to a 10 000-l closed system raceway. From hatching, mantle length increased exponentially at a mean rate of 1.69% per day throughout the experiment. The largest and longest-lived squid attained a maximal size of 77 mm mantle length in 8 months. Only live food organisms, which consisted of copepods, other crustaceans and fishes, were accepted by the squids. Mortality, attributed to starvation and fin damage, was greatest during the first 20 days and again between days 45 and 70.     

Epibionts of pond-reared adult Malaysian prawns,Macrobrachium rosenbergii (de Man), in South Carolina

During 1976, epibionts were noted on adult Malaysian prawns reared in a special ‘brood stock pond’. These epibionts have not previously been recorded on Macrobrachium rosenbergii. Dense algal growths, covering much of the carapace, were observed on 58.3% of the males (mean size, 147.1 g) and on none of the females at harvest. Species composition was primarily (about 90%) the Chlorophyte Oedogonium crassiusculum, with the Cyanophyte Lyngbya, the secondary dominant. The large infested males were sluggish and in some cases functionally blind due to the algal covering. However, once moved to indoor culture tanks the algae were lost and the prawns' behavior returned to normal.Eggs of the water boatman, Ramphocorixa acuminata, were observed on 52.5% of the females (mean size, 78.0 g) and 5.9% of the males at harvest. Egg deposition was limited to the cephalothorax and/or the first and/or second abdominal segments. This epibiont was not noted in the six adjacent rearing ponds containing approximately 84,000 smaller prawns. The insect eggs appeared to cause no injury and disappeared shortly after the infested prawns were returned to laboratory tanks.Although both epibionts exhibited apparent sex specificity in the brood stock pond, data from other rearing ponds did not support this specificity. The occurrence of these epibionts should pose no problem to the successful pond culture of M. rosenbergii in South Carolina.     

Swim bladder inflation and survival of Mugil cephalus to 50 days

Excessive inflation of the swim bladder causes immobility and mortality of 12-day old larvae of Mugil cephalus and other marine fish. Increased aeration or mechanical agitation of the water in rearing tanks maintained the larvae below the water surface, and the swim bladder formed and functioned normally. Survival was dramatically increased. Two experimental production tanks, stocked initially with 15 000 and 20 000 larvae, at a density of 5.25 and 7.0/l, respectively, yielded 33.5% and 16.9% juveniles on day 50. Only an outbreak of ciliated parasites prevented both tanks from having survival figures of over 30%.     

Dietary supplementation of host‐associated lactic acid bacteria modulates growth,metabolic activities,and immune‐related gene expression in giant freshwater prawn,Macrobrachium rosenbergii

The present study was carried out to evaluate the dietary effects of host‐associated lactic acid bacteria on growth performance, metabolic enzyme activities, and immune response of Macrobrachium rosenbergii juveniles. To formulate the test diets, a control (Con) diet was supplemented with a commercial probiotic and three host‐derived bacteria Enterococcus faecalis (EC), Lactococcus lactis I (LC‐I), and L. lactis II (LC‐II), which were previously isolated from the gastrointestinal tract of adult individuals of M. rosenbergii. Juvenile M. rosenbergii (0.65 ± 0.008 g) were randomly stocked at 20 individuals/100 L of fiberglass tanks with three replications for each test diet. After 50 days, juveniles fed the diets LC‐I and LC‐II showed significantly higher (p < .05) weight gain, specific growth rate, and the lowest feed conversion ratio. The analyses of glutamic oxaloacetate transaminase and glutamic pyruvate transaminase in muscle and hepatopancreas revealed significantly (p < .05) reduced values in LC‐I fed juveniles. The total hemocyte count and phenoloxidase activity were significantly increased (p < .05) in LC‐I and LC‐II fed juveniles. The relative mRNA expression patterns of immune‐related α2‐M, LGBP, ProPO, Cu, Zn‐SOD, TG, PE, AKP, and ACP genes were significantly (p < .05) upregulated in juveniles fed with LC‐I followed by the diet LC‐II. Finally, the study suggests that the growth performance and immune response of M. rosenbergii can be improved through supplementation of host‐associated L. lactis bacteria for its higher production.     

Probiotic activity of Bacillus subtilis in juvenile freshwater prawn, Macrobrachium rosenbergii (de Man) at different methods of administration to the feed

This experiment was carried out to investigate the potential probiotic properties of Bacillus subtilis and suitable methods of administration to the commercial feed in juvenile Macrobrachium rosenbergii (de Man) from 25 August to 25 November 2008. Putative Bacillus subtilis bacterium isolated from juvenile M. rosenbergii intestine was added to commercial prawn feed as a probiotic. Five types of diets were prepared by mixing B. subtilis at level of 108 cells g^?1 with commercial feed using different methods consisting mixing, soaking, spraying and bathing. After 60?days, the prawns fed diets at soaking method treated group, showed a higher mean weight gain (2.09) or 328.84% increase in growth over control. There were significant differences (P?<?0.05) in weight gain, feed intake and FCR among soaking method and other treated and control groups. There was significant difference (P?<?0.05) in survival among treated and control groups, but no significant difference (P?>?0.05) in water quality and biochemical composition among treated and control groups. Clearly, B. subtilis-treated diets appeared to enhance growth and survival of juveniles M. rosenbergii. It was concluded that the tested strain may be a promising probiotic for M. rosenbergii under soaking method of administration to the prawn commercial feed.     

Preliminary study on broodstock rearing,induced breeding and grow‐out culture of the sea cucumber Holothuria scabra in Sri Lanka

Experiments were conducted to identify suitable methods for broodstock rearing, induced breeding and grow‐out culture of Holothuria scabra in Sri Lanka. Two hundred and seventy‐two brooders (500–600 g) collected from off Mannar were individually packed in oxygen‐filled polythene bags with and without sea water and transported to a sea cucumber hatchery at Kalpitiya. Lagoon pens, sand‐filled fibreglass tanks and bare tanks were used in triplicates to maintain brooders. Spawning was initiated using air dry, water jet and thermal‐stimulation methods. Hatchery produced juveniles with an average weight of 11 ± 5 g were reared (2 individuals m^?2) in lagoon pens, mud ponds and fibreglass tanks in triplicates. The significantly high evisceration rate was observed when brooders were transported without sea water (t‐test, P < 0.05). Brooders maintained in bare tanks showed a significant weight reduction than the brooders in sand‐filled tanks and lagoon pens (anova , P < 0.05, d.f. = 2). Thermal stimulation (ambient temperature ± 3–5°C) was found to be the most successful method of spawning initiation of H. scabra. The mean (±SD) percentage males and females participated for spawning per trial was 9.2 (±10) and 4.6 (±5.6) respectively. On an average, 1.16 millions of eggs (±1.03 SD, n = 5) were obtained per spawning trial. H. scabra juveniles reared in tanks showed significantly lower growth rate than the juveniles in pens and ponds (anova , P < 0.05). Lagoon pens and sand‐filled tanks are suitable to maintain brooders and lagoon pens can be successfully used for mass rearing of juveniles.     

Economic feasibility of prawn Macrobrachium production in South Carolina,USA

Cost and returns were estimated for freshwater prawn Macrobrachium rosenbergii farming as a supplemental enterprise in South Carolina in relation to the following factors: (1) existing versus new investment for ponds and water supply; (2) three stocking strategies (postlarvae alone, a 50:50 mixture of postlarvae and nursed juveniles and nursed juveniles alone) at various densities (2·15–8·61 prawns m^?2); (3) a range of prices for seed stock ($0–50 per thousand); and (4) two marketing alternatives (sale of product as shrimp tails only or with the large animals marketed heads-on and the rest as tails). Net revenue estimates indicate that prawn aquaculture has potential to become a source of supplemental income to farmers in the coastal plain area of South Carolina and throughout much of the southeastern United States. This is especially likely if the enterprise can utilize existing pond facilities that are already discounted into the value of the land or were constructed during a period of lower investment costs. A prawn farm is unlikely to be profitable if postlarvae alone are stocked, even in existing facilities, but if a mixture of postlarvae and juveniles or juveniles alone are stocked in existing facilities, profitability is likely at seed costs up to about $40 per thousand.     

A comparative study on larviculture techniques for the giant freshwater prawn, Macrobrachium rosenbergii (de Man)

Comparative studies of larviculture of Macrobrachium rosenbergii (de Man) were made for three systems: (1) the static water system with partial changes of water, (2) the closed recirculating water system with a separate subsand filter unit, and (3) the closed recirculating water system with a subsand filter inside the rearing tank. The mean production of juveniles per unit volume of water of these three systems was comparable (3.2, 1.9, and 2.9, respectively). Production fluctuated more in the static system than in the closed recirculating system. A significant asymptotic relationship between the stocking density and the survival of prawn larvae was observed in the first type of the closed recirculating system; higher stocking density resulted in lower survival. A stocking density of 20 larvae/l in the closed recirculating system was considered to be good for growth and survival. The intermittent high nitrite level was a problem encountered in the static system but not in the closed recirculating system. The operational costs of these three systems were discussed.     

Experiments in rearing rabbitfish (Siganus rivulatus) in sea water

The initial experiments in rearing rabbitfish (Siganus rivulatus) in sea water indicate that this fish may be suitable for commercial cultivation. Juveniles are available in large numbers during summer and fall along the Mediterranean and Red Sea coast of Israel. Juveniles collected in Eilat (Red Sea) were kept in tanks and submerged cages and fed fish pellets. After 29 days in tanks, the first group of fish which averaged 0.91 g upon capture increased in weight to an average of 3.7 g. A subsequent school of juveniles kept in sea cages for 84 days increased in weight from an average of 7.3 g to 28.5 g.     

An intensive hatchery rearing protocol for larvae of the bullseye puffer,Sphoeroides annulatus (Jenyns)

In this study bullseye puffer, Sphoeroides annulatus larvae were reared from hatching through to 1 or 2 months after weaning on an experimental scale in three replicate 600 L tanks and on three occasions during the spawning season (nine tanks in total). The rearing protocol used was green water (Nannochloropsis oculata and Isochrysis sp.) 100 000 cells mL^?1 from 0 to 11 days after hatch (DAH), 5–10 rotifers, Brachionus rotundiformis mL^?1 from 2 to 26 DAH, 0.1–1 Artemia mL^?1 from 21 to 34 DAH and weaning from 29 to 34 DAH. Survival to a month after weaning was 1%, a total of 3153 juveniles were produced with an average wet weight of 0.29 ± 0.07 g and a length of 27.5 ± 0.82 mm.     

The mass outdoor culture of macroscopic marine algae

Two species of macroscopic marine algae (Rhodophyceae) were grown and harvested continuously during 1974 in Fort Pierce, Florida. The seaweeds Gracilaria sp. and Hypnea musciformis were grown in both 600-l and 350-l tanks in the third stage of a nutrient removalaquaculture process that included microscopic marine algae and oysters in the first two stages. Mixtures of secondary-treated waste water and sea water constituted the initial nutrient source, with the seaweeds utilizing nutrients not assimilated by the microscopic algae and/or generated by the oysters. Standing crops of up to 7 900 g wet weight of Hypnea and 9 000 g Gracilaria were maintained. The Hypnea cultures could not be maintained in summer when tank temperatures reached 30°C, but Gracilaria grew during the entire year. On the basis of periodic harvesting, yields were consistently between 12 and 17 g dry weight per m² per day for both species. These yields are as high as those achieved by mass cultures of microscopic marine algae, or by fast growing commercial crops such as sugar and rice.     

Critical swimming speed and maximum sustainable swimming speed of juvenile Pacific bluefin tuna, Thunnus orientalis

Tank wall collision is one of the major causes of mortality during the early-stage rearing of Pacific bluefin tuna, Thunnus orientalis (PBT). Therefore, to design a rearing environment that meets the needs of juvenile PBT, it is important to gather information about their swimming capabilities. We conducted experiments to examine the relative critical swimming speed (RCSS) and maximum sustainable swimming speed (MSSS) of early-stage PBT. The fish were kept in 3-tonne tanks and fed on artificial pellets every 2 h from dusk to dawn. We conducted two sets of experiments to measure swimming speed; the fish were introduced one at a time into a water funnel, and the water current velocity was gradually increased over time to estimate RCSS, or the water current was kept at a constant velocity to estimate MSSS. We measured the RCSS of 72 PBT juveniles (24–29 days after hatching (DAH); standard length (SL), 15.0 ± 2.3 mm) and the MSSS of 32 PBT juveniles (28–37 DAH; SL, 20.0 ± 5.1 mm) in the laboratory. The RCSS ranged from 4.7 to 20.3 SL/s (average, 12.4 ± 3.3 SL/s), and the MSSS was estimated to be approximately 4 SL/s. We speculate that introducing a water current in the rearing tank of no more than 4 SL/s could positively affect the survival of juvenile PBT.     

UV treatment in RAS influences the rearing water microbiota and reduces the survival of European lobster larvae (Homarus gammarus)

The rearing environment is important for a stable production of good quality lobster juveniles. By providing an environment excluding pathogens and dominated by mutualistic bacteria, the probability of developing healthy host-microbe relationships and produce healthy juveniles is increased. Disinfection of water and sudden increase in the supply of organic matter in culture tanks are processes that open for uncontrolled microbial regrowth in the rearing water. This increase the variability in the development of the microbiota between replicate rearing tanks and promotes selection for potentially harmful opportunistic bacteria. In two start feeding experiments with European lobster (Homarus gammarus) we compared the bacterial environment in three types of rearing systems: a recirculating aquaculture system (RAS) with UV treatment directly in front of the rearing raceways, a RAS without disinfection, and a conventional flow through system (FTS). The RAS with no disinfection was hypothesised to stabilise the microbiota of the rearing water, select against opportunistic bacteria, and reduce variability in production outcome between replicate tanks compared to the other systems. As predicted, the three different systems developed significantly different compositions of the microbiota in the rearing water and the larvae. On average, the survival of larvae in RAS without disinfection increased with 43 and 275 %, in the first experiment, and 64 and 18 % in the second experiment, compared to RAS with UV and FTS, respectively. Also, the RAS without disinfection showed less variability in the survival of larvae between replicate tanks and batches compared to the other treatments. The results are promising for controlling the microbiota of the rearing water to improve, increase and stabilise the production of marine larvae by competent use of water treatment and selection regimes. Based on the presented and previous work, RAS is recommended over FTS, and in RAS it is recommended to avoid point-disinfection of the recirculating water, to provide a stable and beneficial microbial environment in the cultivation of marine larvae.     

Observations on salinity tolerance and osmoregulation in laboratory-reared Macrobrachium rosenbergii post-larvae (Crustacea: Caridea)

The tolerance of postlarval Macrobrachium rosenbergii to gradual and rapid increases in salinity was determined. Mortalities occurred at salinities around 25‰ and increased rapidly at levels ≥30‰ in both cases. However, acclimation substantially increased survival time at 35‰.Freezing point depressions of blood were measured from laboratory-reared M. rosenbergii postlarvae and juveniles exposed to various salinities from fresh water to approximately 35‰. The blood concentration was hyperosmotic to the medium at salinities from fresh water to about 17–18‰ and hypoosmotic at higher salinities. Postlarvae maintained a nearly constant blood concentration (freezing point depression = ?0.89 ± 0.13°C) over a wide range of external salinities (fresh water to about 27–30‰). The animals' osmoregulatory mechanisms failed at salinities ≥30‰, and thereafter the blood concentration paralleled that of the medium. The blood concentrations of juvenile shrimp grown for 5 months at salinities from fresh water to about 15‰ (freezing point depression = ?0.88 ± 0.07°C) closely resembled those of postlarvae.The osmoregulatory performance of young M. rosenbergii is generally similar to that of other brackishwater animals, but in their ability to hyperosmoregulate effectively in fresh water they more closely resemble fresh water species. It is suggested that M. rosenbergii may be able to conserve salt in dilute media by producing blood-hypoosmotic urine.An interesting stress symptom often preceded death of postlarvae in high salinities. The animals changed gradually from nearly transparent to opaque white and then died, usually within a day or so.