Comparison of three fish-loading systems to harvest food-size channel catfish (Ictalurus punctatus)

Three fish-loading systems were used to harvest food-size channel catfish (Ictalurus punctatus). Loading rates of equipment and their effect on post-harvest fish survival and weight gain during cool and warm weather were studied.

The turbine pump loading rate (300·7 kg/min) was greater than the lift net (158·00 kg/min) and vacuum pump (54·1 kg/min), while the lift net was greater than the vacuum pump (p < 0·05).

Mean survivals (± SD) for catfish loaded by lift net, turbine pump and vacuum pump from earthen ponds during cool and warm weather were 96·6% (±2·8), 93·9% (±7·4) and 97·7% (±1·1) and 94·0% (±5·7), 85·3% (±8·6) and 89·0% (±12·5), respectively. Mean weight change (± SD) per catfish loaded by the same equipment during cool-and warm-weather tests were −8·2 g/fish (±31·1), −12·4 g/fish (±15·2) and −17·5 g/fish (±19·9), and 67·6 g/fish (±60·6), 33·9 g/fish (±137·4) and 32·4 g/fish (±142·1), respectivley. There were no significant differences among loading systems for survival or mean weight change per fish. The turbine pump is a possible alternative to the traditional life net as a means of loading food-size channel catfish. Further testing on commercial catfish farms is required.     

Water budgets for fish ponds in the dry tropics

Water budgets were calculated for embankment fish ponds located in the dry tropics. Two 5-month studies were conducted at Comayagua, Honduras. Daily pond evaporation averaged 0·55 ± 0·22 and 0·64 ± 0·17 cm during studies 1 and 2, respectively. Pond evaporation was 14·5% greater during study 2. Significantly greater pond evaporation was measured during the 3 driest months compared to the 3 rainiest months. Mean daily seepage ranged from 0·11 to 0·43 cm and from 0·06 to 0·60 cm during studies 1 and 2, respectively. Total rainfall during study 1 exceeded that during study 2 by 43%. Regulated inflow water was required every month to replace water losses to pond evaporation and seepage. Pond evaporation accounted for 70% of total water loss during both studies, while seepage accounted for the remaining water loss. Rain accounted for 45·5 and 21·8% of gains during studies 1 and 2, respectively. Regulated inflow water accounted for 52·8 and 77·9% of the respective gains.     

Gas phase axial dispersion in a packed column oxygen absorber

Gas phase axial dispersion was characterized within an enclosed packed column receiving oxygen and water under counter-current flow conditions. Steady-state gas phase profiles (longitudinal) were measured during a series of 90 column runs in which, at each of three bed depths (0·362, 0·699, and 1·041 m), all combinations of the following independent variables were tested: influent volumetric oxygen-liquid ratio, 0·8, 1·6, 2·6, 4·0, and 8·0%; hydraulic loading, 32·0 and 61·2 kg/m² s; and packing type, 2·54 cm Tri-Pack^®, 3·81 cm Nor-Pac^® and 5·08 cm Nor-Pac^®. Over the range of operating conditions tested, gas phase mixing was extensive and for all practical purposes could be considered complete. A homogeneous gas phase within the column, unlike true counter-current flow, results in an exponential decay in dissolved gas deficits as the liquid passes through the packing. Thus, increases in packed bed depth will result in diminishing increases in gas absorption/desorption.     

Growth potential of wild juvenile Penaeus stylirostris in earthen ponds receiving chemical and organic fertilizers, and pelleted feed

The growth potential of wild juvenile Penaeus stylirostris was analyzed in experimental trials using chemical and organic fertilizers and pelleted feed in 0·25 ha earthen ponds. Shrimp were stocked at a low density (1·6 ind/m²). After 103 days, final weight ranged from 9·5 to 26·0 g. The significance of differences in growth response was determined using a reparameterization of the von Bertalanffy growth curve. Maximum growth rates observed in the trials ranged from 0·06 to 0·33 g/day, averaging 0·22 g/day. Maximum rates were related to weight by the equation:

(dw/dt)_max=0·034w^0·69 r²=0·9,P<0·05

Pelleted feed produced best growth, chemical fertilizers were acceptable, and organic fertilizers gave poor results. The high growth potential of the species stimulates future research in order to adapt a culture technology to the semi-arid conditions of northwest México, where the species is indigenous.     

Thermal disinfection of seawater for aquacultural purpose

The dose of heat required to kill Vibrio anguillarum has been determined. The results show that > 99·97% inactivation was obtained after 3 min exposure to 44·0°C. After 2 min exposure to 47·5°C, > 99·99% inactivation was obtained. The results indicate that heating is a useful method for safe disinfection of small amounts of water.     

Measurements of oxygen consumption and ammonia excretion of Atlantic salmon (Salmo salar L.) in commercial-scale, single-pass freshwater and seawater landbased culture systems

The oxygen consumption of Atlantic salmon was measured in large culture tanks for a period of 20 months from the parr to the adult stage. In addition, diurnal sampling was conducted for estimation of both oxygen consumption and ammonia excretion. The oxygen consumption was affected especially by temperature, season and smoltification. For parr the oxygen consumption rate was 1–6 mg O₂/kg min and the ammonia excretion rate was 0·037–0·13 mg N/kg min from autumn to spring. The corresponding rates for adult salmon during the period October to July were 1·5–4·5 mg O₂/kg min and 0·075–0·13 mg N/kg min.     

A laboratory scale recycling water unit for tilapia breeding

The technical features of a laboratory scale water recycling unit for experimental small scale tilapia breeding are described. Two units (1 and 2) were operated during a 6 month period, carrying a similar fish load (7·5 kg) and feeding rate (2% fish body weight/day). Unit 1 received natural illumination, while unit 2 was artificially illuminated (14/10 - light/dark cycle). Both units were equipped with a biological filter bed (substrate surface area, 3500 cm²). In unit 1, total ammonium and nitrite concentrations ranged from 0·05 to 0·5 mg liter⁻¹, while nitrate varied between 10–40 mg liter⁻¹. In unit 2 corresponding values were 0·15-3 mg liter⁻¹, 0·05–0·8 mg liter⁻¹ and 10–40 mg liter⁻¹. Temperatures ranged between 20–29°C and pH values between 7·5–6·9 in both units. Dissolved oxygen concentrations decreased gradually from 5·6 to 3·4 mg liter⁻¹ in unit 1 and from 5·6 to 2·6 mg liter⁻¹ in unit 2. Twenty-six spawnings occurred in unit 1 in March and April, while only eight spawnings occurred in unit 2, possibly because of the absence of sunlight. The significance of these results are discussed.     

Performance of the amazonian tambaqui, Colossoma macropomum, in pond polyculture

Tambaqui (48%) was reared in polyculture with grass carp (27%) and curimbatá (25%) from 75 g mean weight for a period of 164 days. Ponds of 1200 m² were stocked at a total density of 12720 ha⁻¹. Fish were fed with an experimental diet made from soybean and maize at a daily rate calculated as 3% of the tambaqui biomass. Grass carp received chopped angola grass at a daily rate of 15% of live weight. Ponds were weekly manured with 120 kg of mixed cattle and goat manure. Tambaqui reached a final weight of 492 g. Survival rate was 83%. The experimental polyculture had a mean net yield of 7·5 t ha⁻¹ year⁻¹, with apparent conversion rates of 1·13, 5·5 and 7·7 kg kg⁻¹ of diet, grass and manure, respectively. All three species had a high growth rate (from 1·2 to 2·1 % day⁻¹). Tambaqui's growth was affected by the fall in water temperature in the second part of the experiment. Cost/benefit calculations proved the high profitability of the tested semi-intensive polyculture system.     

Performance of packed column aerator at low hydraulic loading

A laboratory-scale packed column aerator filled with ceramic Raschig rings was tested for its performance with hydraulic loadings in the range of 16–86·3 m³ m⁻² h⁻¹. Two columns of 0·19 m and 0·24 m inside diameter and packing sizes of 15, 25 and 36 mm were used. The system equation developed by previous workers for trickling filters in waste-water treatment was not generally applicable across the lower hydraulic loadings. The system coefficient incorporating the oxygen absorption coefficient (k_La) was found to vary within the range of hydraulic loadings studied. The oxygen transfer rate equation developed for surface and submerged aerators was used for estimating standard oxygen transfer efficiency of the packed column aerator, which, in this case, ranged from 6·2 to 22·6 kg O₂ kWh⁻¹.     

Bacterial diversity of tilapia (Oreochromis niloticus) cultured in brackish water in Saudi Arabia

The bacterial flora occurring in brackish pond water, sediment, gills and intestine of healthy tilapia cultured in Saudi Arabia were estimated both quantitatively and qualitatively, and the isolates were identified to genus or species level. Total viable count of bacteria ranged from 1.4±1.5×10³ to 8.6±2.7×10³ cfu ml⁻¹; 1.2±3.1×10⁶ to 7.3±1.1×10⁷ cfu g⁻¹; 8.7±1.9×10⁵ to 2.1±0.9×10⁶ cfu g⁻¹; and 2.8±2.4×10⁷ to 1.0±1.6×10⁸ cfu g⁻¹ in the pond water, sediment, gills and intestine of brackish water tilapia, respectively. In total, 19 bacterial species were identified. The bacteria were predominantly Gram-negative rods (87%). Pond water and sediment bacteria influenced the bacterial composition of gills and intestine of tilapia. In contrast to gill bacteria, more diversification was observed in intestinal bacteria. The predominant (prevalence >10%) bacterial species were Vibrio parahaemolyticus, Vibrio carchariae, Vibrio alginolyticus, Chryseomonas sp., Vibrio vulnificus, and Streptococcus sp. in all the populations with the exception of the sediment population where Streptococcus sp. was replaced by Shewanella putrefaciens. Vibrio spp. (58% of the total isolates) dominated the total bacterial population.     

南澳贝藻混养互利机制的初步研究

以牡蛎和龙须菜为试验材料,进行了两个阶段不同投放比例的室内模拟混养试验,试验周期均为4周,各试验组分别为:对照组、龙须菜单养组、牡蛎单养组、牡蛎龙须菜低密度混养组、牡蛎龙须菜中密度混养组和牡蛎龙须菜高密度混养组,其中除对照组和龙须菜单养组外,各试验组牡蛎密度均为27只/m3,第一阶段龙须菜密度分别为:0,47,0,47,94,188g/m3,第二阶段龙须菜密度为:0,158,0,158,316,854g/m3。定期采样测定水体中营养盐(NO2-N,NO3-N,NH4-N,PO4-P)的含量及养殖生物的生长情况。试验结果表明,第一阶段试验结束时,投放牡蛎的试验组与未投放牡蛎的试验组水体氮、磷含量差异显著(P0.05)。第二阶段试验结束时,投放牡蛎的各试验组磷酸盐和硝酸盐含量差异显著(P0.05),高密度混养组的磷酸盐含量和硝酸盐含量与牡蛎单养组相比分别降低了43%、30%,说明龙须菜明显吸收了水体中的氮、磷,混养系统氮、磷利用更为合理,其中龙须菜854g/m3,牡蛎27只/m3的高密度混养组投放密度最为合理。     

Effect of water temperature on the immune response of white shrimp Litopenaeus vannamei to Vibrio alginolyticus

White shrimp Litopenaeus vannamei held in 25‰ seawater at 27 °C or 28 °C were injected with TSB-grown Vibrio alginolyticus at 1 × 10⁴ colony-forming units (cfu) shrimp^− 1 or 1 × 10⁵ cfu shrimp^− 1, and then cultivated onward at water temperatures varying from 20 to 34 °C. Over 24–144 h, mortality of V. alginolyticus-injected shrimp held at 34 °C or 32 °C was significantly higher than that of shrimp held at lower temperatures. In a separate experiment, shrimp held in 25‰ seawater at 28 °C and then cultured onward at 20 to 32 °C were examined for immune parameters at 24–96 h. THC, phenoloxidase activity, respiratory burst, and SOD activity decreased significantly at 24 h after transfer to 32 °C. Shrimp held in 25‰ seawater at 27 °C and then cultured onward at 20 to 34 °C showed a significant reduction in phagocytic activity and clearance efficiency for V. alginolyticus at 24 h after transfer to 34 °C. It was concluded that transfer of shrimp from 27 or 28 °C to higher temperatures (32 and 34 °C) reduced their immune capability and decreased resistance to V. alginolyticus infection.     

Quantitative measurement of reproductive output in the American oyster, Crassostrea virginica (Gmelin), using an enzyme-linked immunosorbent assay (ELISA)

Abstract. A quantitative gonadal index was developed for oysters, Crassostrea virginica (Gmelin. 1791), using polyclonal antibodies from eggs and sperm. Percoll used in the purification of oyster eggs and sperm greatly improved the purity of antigens compared to filtering the egg or sperm through a fine mesh only. The antigen-antibody reaction was tested with indirect sandwich ELISA using alkaline phosphatase-conjugated goat anti-rabbit igG as a secondary antibody. Rabbit anti-oyster egg IgG and anti-oyster sperm IgG initially exhibited a weak cross-reactivity over somatic tissue. Absoring with acetone-dried oyster tissue powder removed this cross-reactivity. Both antisera exhibited strong specific immunological reactions to oyster eggs or sperm respectively. The quantity of eggs or sperm was measured using ELISA and a quantitative gonadosomatic index (dry wt of egg or sperm/dry wt oyster) (GSI) calculated. GSI from ELISA correlated with gonadal stage measured histologically. Monthly mean GSI of female oysters was highest during late spring to early summer (0·157–0·201) and lowest during early winter to early spring (0·002-0·000). Maximum GSI observed during the study was 0·422 for female oysters and 0·446 for male oysters. Female oysters produce 3·7–65·4 million eggs, with an average of 21·1 million during each spawning. A positive correlation was observed between the number of eggs produced and oyster size; the number of eggs in the gonad increased as oyster size (i.e. total dry wt) increased (r= 0·67); however, the relationship was non-linear. Large oysters contained proportionally fewer eggs. Prevalence of Perkinsus marinus parasitism was high, 90–100%, during the study, as was weighted incidence, 1·33 to 2·67, No statistically significant correlation was observed between infection intensity and the per cent weight of oyster eggs or egg number.     

Changes in the distribution of epifaunal reefs and oysters during 130 years of dredging for oysters in Foveaux Strait,southern New Zealand

1. Foveaux Strait, a narrow seaway that is exposed to heavy wave action and strong tidal currents, has been the subject of an oyster fishery for over 130 years. Before the oyster fishery commenced the seafloor was extensively covered by epifaunal reefs that were tidally‐oriented, linear aggregations of patch reefs. 2. Patch reefs are formed by the bryozoan Cinctipora elegans cemented by encrusting bryozoa, ascidians, sponges, and polychaetes. The molluscan epifauna is dominated by the oyster, Tiostrea chilensis and bysally attached bivalves. Mortality of oysters is probably lower and recruitment and growth may be higher within the reef habitat. 3. Fishers found commercial densities of oysters occurred only on epifaunal reefs. Fishers exploited local groups of reefs. These groups form the patchily distributed oyster beds characteristic of this fishery. 4. Dredging for oysters progressively modified reefs until oysters were the only epifauna remaining. Dredges caught oysters more efficiently after the catch bag no longer became saturated with other epifauna. This heightened efficiency allowed fishers to rapidly reduce oyster density to commercial extinction. Oyster density has not rebuilt on oyster beds abandoned by fishers. 5. The rate of modification of epifaunal reefs was slower during the early years of the fishery but has accelerated, especially over the last 37 years. Frequency of disturbance increased as the numbers of vessels fishing grew and fishers developed speedier dredging methods. Intensity of disturbance also increased as heavier dredges were introduced and allowed focused fishing of reefs. 6. Oysters became reduced to low densities in the eastern and central areas that fishers then abandoned. The commercially exploited area subsequently expanded to the limits of Foveaux Strait. 7. With accelerated modification of oyster habitat, disease mortality has become more important. 8. Attempting to rebuild the fishery by oyster enhancement may be more successful conjoined with habitat restoration. Copyright © 1999 John Wiley & Sons, Ltd.     

Comparative analysis of Vibrio splendidus-related strains isolated during Crassostrea gigas mortality events

French mollusc production is based mainly on the Pacific cupped oyster, Crassostrea gigas. Since 1991, annual mass mortality of juveniles has been reported during summer months. These recurring episodes concern professionals who fear that like Portugese oyster, C. angulata, C. gigas could in turn disappear following one of these epizooties. Previously, bacteriological analysis of moribund oyster juveniles yielded an isolate of a Vibrio splendidus biovar II strain, named TNEMF6. This isolate was demonstrated to be pathogenic to Crassostrea gigas spat by experimental challenge. To study the association between summer oyster mortality and presence of TNEMF6 cluster strains, Vibrionaceae fauna were isolated from infected spat along the French Atlantic coast between 1997-1998. Strains related to V. splendidus biovar II were selected. Comparison with TNEMF6 was performed by classical biochemical tests and polymerase chain reaction – restriction fragment length polymorphism (PCR-RFLP) of SSU rDNA, rpoD, and gyrB genes. Genomic similarities were confirmed by DNA/DNA hybridization. Only one strain out of 14, TNNIII7, was found to be closely related to the pathogenic bacteria. Neither the phenotypic nor the genotypic markers used in this study were able to distinguish pathogenic from non-pathogenic strains of the widespread V. splendidus. However, future genetic comparisons of TNEMF6 and TNNIII7 is likely to reveal genes involved in pathogenicity.     

Conchiolin infection and surface coating Vibrio: shell fragility, growth depression and mortalities in cultured oysters and clams, Crassostrea virginica, Ostrea edulis and Mercenaria mercenaria

Abstract. A disease of cultured juvenile European oyster, Ostrea edulis , and American oysters, Crassostrea virginica , was characterized by infection of conchiolinous ligament and periostracum by surface-coating Vibrio spp. bacteria. A similar bacterium was isolated from diseased cultured hard clams, Mercenaria mercenaria , held in a facility about 300 km distance from the oyster hatcheries. The oysters demonstrated fragile, undercalcified peripheral shell and apparently excessive chalky deposits. Histological and scanning electron microscopical examination revealed that the oysters' eroded ligaments and perforated peripheral periostracum were infected with uniform rod-shaped bacteria. The infection appeared to interfere with normal proteinaceous and calcareous shell deposition and possibly with normal ligament function. Histological examination of the digestive system organs suggested that normal digestive processes were also interrupted. Two predominant bacteria were isolated from oyster samples and one predominant bacterium was isolated from clam samples. One of the isolates from oyster culture facilities was found almost exclusively associated with oyster shell surfaces and culture tank surfaces, this isolate was similar to the one taken from clam shell surfaces. The other predominant bacterium was found in water column samples in oyster culture facilities at levels from about 10⁵ to 10⁷ per ml. This isolate had a DNA base ratio (moles % G + C) of 43.6; the two surface-associated isolates had base ratios of 43.6 and 44.5%. These Gram-negative, oxidase positive, fermentive rods have been identified as a Vibrio spp. group. Specific antibody was produced which differentiated these bacteria from each other and from other similar isolates. Practical procedures for controlling the bacteria in shellfish culture systems are described.     

Consumer Preference and Sensory Properties of the Pacific Cupped Oyster (Crassostrea gigas) and the European Flat Oyster (Ostrea edulis)

ABSTRACT

Experts in the oyster supply chain (farmers, retailers, and gourmet chefs) in The Netherlands have suggested that the European flat oyster (Ostrea edulis) has superior sensory qualities compared to the Pacific cupped oyster (Crassostrea gigas). However, scientific evidence is lacking. The aim of this study was to evaluate consumer preferences for these two oyster species and to determine the sensory properties of both species by consumers. Two-alternative forced choice tests were performed with the oysters involving a panel of 74 naïve consumers. No significant differences in preferences between the oyster species were observed by the consumers. Nine sensory attributes of both oyster species were evaluated. Consumers did not observe significant differences between species in the sensory attributes: overall odor intensity, sea odor, mud odor, sweetness, pungency, and firmness. The Pacific cupped oyster was perceived as significantly saltier and more intense in greenness than the European flat oyster. We concluded that only a few sensory properties of the European flat oyster and the Pacific cupped oyster are perceived as being different by untrained consumers.     

太平洋牡蛎筏式养殖高产试验

利用筏式吊养使牡蛎胃中泥沙含量达到出口标准，试验面积４００亩，经１５个月暂养和养成，平均亩产６５９２．８ｋｇ，规格９．４ｃｍ，总产值７９１．１万元，利润４１１．７６万元，平均亩盈利１．０３万元。经专家鉴定，本研究达到国内先进技术水平。     

Enrichment of Artemia with free methionine

Different enrichment procedures of the free amino acid (FAA) methionine were tested for Artemia nauplii. A direct enrichment protocol (methionine dissolved in the culture water) was compared with liposome enrichment protocols that varied in their membrane composition. During 16 h of direct enrichment in 5.3 mM methionine, the nauplii increased their content of free methionine between 20 and 30 times compared to the unenriched control (43.1±1.2 and 68.4±3.8 pmol·nauplius⁻¹ in two separate experiments vs. 2.4±1.0 pmol·nauplius⁻¹ in control). However, by encapsulating the identical amount of methionine into liposomes made from pure egg yolk phosphatidylcholine (PC) (>99% PC) and cholesterol, the nauplii content of free methionine reached 148.8±27.6 pmol·nauplius⁻¹, which is approximately 60 times more than in the unenriched control. Another liposome composition tested, made from crude egg yolk PC (>60% PC) and cholesterol, resulted in 90.5±4.1 pmol·nauplius⁻¹. The enriched nauplii still retained 80% of the free methionine after 8 h of incubation at conditions simulating feeding for Atlantic halibut larvae (13°C, 33.5 g·l⁻¹).

In conclusion: (1) Artemia nauplii can successfully be enriched with free methionine, (2) the high retention of free methionine in the Artemia nauplii following transfer to fish tanks shows that it is possible to offer fish larvae a feed with a high level of FAA, based on enrichment of Artemia nauplii.     

New oyster on-growing container for German mariculture operations

The hydrographic and climatic situation along the German coast requires specially adapted equipment for mariculture enterprises. The containers used in the past for the on-growing of oysters (Crassostrea gigas Thunberg) in shallow sea areas provided results which gave reason for developing a new type of container which was to be more economic and produce a high quality oyster of uniform shape.Small prototype containers, based on a galvanized iron construction, were built and placed at different sites along the coast. They held 1680 oysters, each of which were re-attached with cement onto square mesh plastic netting which was stapled on oak frames. On these frames, which were handled like drawers, the oysters had optimal conditions which were believed to be better than on a natural oyster bed. Each oyster had its own space of 7 cm by 8 cm wide and 10 cm high and was not handled until it reached market size. Good water exchange was provided by the open construction of the container which also gave protection against predators by means of a complete mesh cover.