The culture, zooplankton dynamics and predator-prey interactions of Chesapeake Bay striped bass, Morone saxatilis (Walbaum), in estuarine ponds

Abstract. Four 0.05-ha research ponds were filled with brackish water (12 ppt) for the purpose of evaluating zooplankion dynamics and predator-prey interactions. Three of the ponds were stocked with Chesapeake striped bass, Morone saxatilis (Walbaum). All ponds were fertilized to stimulate zooplankton blooms using a protocol that has been successful in freshwater systems. Zooplankton was dominated by four major groups: rotifers, copepod nauplii, Eurytemora adults and Eurytemora copepedites with rotifers and the nauplii being the most abundant organisms found. Rotifer populations peaked 15-20 days after filling while the copepods peaked 17-22 days after filling. Fish production was very similar to that found in freshwater ponds with an average yield of 84.4 kg/ha (2.0 kg/ha/day) for phase 1 fish (=45mm). Food selectivity indices indicated striped bass avoided both rotifers and copepod nauplii and preferred adult and copepedite Eurytemora as a food item. However, due to various problems associated with sampling, these selectivity results should be considered with caution. The findings of this study reveal fertilization regimes used successfully in freshwater production systems can be applied in an estuarine environment.     

Effects of trichlorfon, fenthion, and diflubenzuron on the zooplankton community and on production of reciprocal-cross hybrid striped bass fry in culture ponds

The application of trichlorfon, diflubenzuron, or fenthion to fertilized culture ponds stocked with 5-day-old, reciprocal-cross, hybrid striped bass fry resulted in an initial reduction in the concentration of rotifers and longer-term alteration of zooplankton successional stages, including changes in concentrations of rotifers, cladocerans, and copepods. Culture ponds without applied chemicals had the highest concentrations of small rotifers when fry were stocked, followed by high concentrations of cladocerans, copepod nauplii, and adult copepods. Fry survival in untreated ponds was higher than in chemically-treated ponds. Initial high concentrations of copepods in some ponds corresponded with low fry survival. Untreated ponds that were filled at the time of broodfish spawning, and stocked with fry 5 days later, had the highest fry survival rates, corresponding with peak rotifer concentrations, followed by a typical zooplankton succession.     

Effect of Environmental Factors on Development of Rotifer and Copepod Nauplii Populations in Sunshine Bass Morone chrysops×M. saxatilis Nursery Ponds without Fish

Knowledge of the effect of environmental factors on timing and production of zooplankton populations would enable sunshine bass Morone chrysops × M. saxatilis farmers to stock fry when live food is most available and thereby increase fry survival. Relationships of morning water temperature, morning and average daily air temperature, day length, number of rain days and daily rain fall, and dissolved oxygen concentrations to time required for rotifer and copepod nauplii populations to peak in freshly filled freshwater nursery ponds was determined. Relationships of the same independent variables to concentrations of rotifers and copepod nauplii at the peak were also determined. For rotifers, day length, dissolved oxygen, and water and air temperatures were highly correlated with time to the peak density, but not concentration of rotifers. Time required for copepod nauplii densities to peak was associated with rain events; whereas, nauplii concentration was related to day length, dissolved oxygen levels and, to a lesser extent, water and air temperatures. Regression equations of the independent variables had very low predictive value for rotifer or nauplii densities or time to reach initial peak nauplii populations. Regressions of day length, morning water temperature, morning and average daily air temperature had moderate values ( r ² > 0.7) for predicting time to initial peak rotifer densities.     

Shrimp pond zooplankton dynamics and the efficiency of sampling effort

The abundance and species composition of zooplankton assemblages were examined in a commercial Penaeus monodon (Fabricius) aquaculture pond in subtropical Australia. Numbers and biomass of zooplankton in the surface tows (142 µm mesh) varied from 2080 L^?1 (2466 µg L^?1) to < 1 L^?1 (15 µg L^?1). Peak zooplankton abundance and biomass occurred at the beginning of the shrimp farm season. The small copepod Oithona australis Nishida was dominant during these peaks in abundance although other species were common, including small, low‐salinity copepods in the first year and larger marine copepods in the second year. Irrespective of taxa or size, zooplankton abundance declined rapidly after the stocking of P. monodon postlarvae, indicating high levels of non‐selective predation. For the remainder of the grow‐out season, mean zooplankton abundance was below 1 L^?1 in the first season and below 3 L^?1 in the second season. The factors that maintain the abundance of these zooplankton assemblages at these relatively low levels are poorly understood but may include a deterioration pond water quality. At these lower levels of abundance, the copepods Acartia pacifica Steuer and Acartia sinjiensis Mori were relatively common during the middle phase of the production season, with barnacle nauplii increasing in abundance during the later stages of the grow‐out season. Analysis of fixed effects showed that there were significant differences in total zooplankton abundance between farm production seasons and occasion within season, and time (day or night). Analysis of random effects demonstrated that the dominant source of variation, in total zooplankton abundance, was day‐to‐day changes within sampling occasions. The complexity of temporal and spatial patterns in the abundance, distribution and composition of zooplankton assemblages in shrimp ponds presents significant challenges in designing sampling programmes that accurately quantify temporal or spatial trends. Our results have shown that sampling for more than four consecutive days, at more than one site, is necessary to accurately assess such trends.     

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.     

云斑尖塘鳢仔鱼饵料动物的非纯化培养及摄食试验

利用塘泥和水体中的浮游动物种源,对云斑尖塘鳢(Oxyeleotris marm oratus)仔鱼的饵料动物进行非纯化培养并做了仔鱼的摄食试验。结果表明:培养过程中,各类饵料动物组成1~8 d以轮虫类占绝对优势,比例达到50%以上,9~10 d以枝角类和桡足类无节幼体占优势,比例达到30%以上;各类饵料动物密度变化曲线呈倒“V”字型,其中饵料动物总密度、轮虫类和枝角类密度均在第7 d达到最高值,分别为47.6个/mL、29.5个/mL和16.5个/mL。从仔鱼对饵料的摄食比率看,大小范围为50~100μm的饵料动物仅适合9日龄以下的仔鱼摄食,随着仔鱼的发育,趋向于摄食较大个体的饵料动物。     

The Effect of Continual,Nocturnal, or No Aeration on Water Chemistry and Plankton Standing Crops in Highly-Fertilized Sunshine Bass,Morone chrysops × M. saxatilis,Fingerling Production Ponds Without Fish

ABSTRACT

Production of fingerlings from very small fry depends upon an initial high concentration of rotifers followed by high densities of crustacean zooplankton. High fertilization rates lead to increased zooplankton production but often cause poor water quality conditions that aeration may alleviate. This study was designed to determine the effects of constant, nocturnal, and no aeration on water quality, primary productivity, and standing crops of phytoplankton and zooplankton in heavily fertilized nursery-size ponds that contained no fish.

Four 0.04-ha ponds were aerated continually; four ponds were aerated only at night with a 372-W (1/2 hp) paddlewheel aerator; and four ponds were not aerated. For 21 days after they were filled on July 21, 1999, the ponds received 1,224 kg/ha rice bran and 581kg/ha liquid 9-27-0 fertilizer. Water quality variables, primary production, chlorophyll-a and zooplankton were sampled daily.

Constant aeration resulted in several conditions more conducive to survival of fish fry, such as higher zooplankton densities, more moderate temperatures, and safer dissolved oxygen levels than did nocturnal aeration or no aeration. However, the development of a higher standing crop of phytoplankton and higher total ammonia concentrations in the turbulent, constantly aerated ponds resulted in higher un-ionized ammonia levels that were not favorable to survival and growth of fry. The high concentrations of zooplankton that developed in the aerated ponds have good potential for cropping to inoculate other ponds or to provide live foods for tank culture of zooplanktivorous fish.     

Disinfection, Microbial Community Establishment and Shrimp Production in a Prototype Biosecure Pond

Plankton community establishment and shrimp production in a prototype biosecure pond were compared to three control ponds. The biosecure pond was enclosed and intake water was disinfected, while control ponds were neither enclosed nor disinfected. All ponds were managed with no water exchange and stocked with 100 postlarvae/m², Litopenaeus vannamei . Residual oxidant concentrations in the biosecure pond dropped rapidly after cessation of chlorinated water addition. This was followed by a sharp increase in water column bacterial abundance, after which the pond was fertilized and inoculated with cultured Chaetocerous gracilis . After crash of the initial C. gracilis bloom in the biosecure pond, this species was not observed again. Following initial large fluctuations in biosecure pond bacterial abundance, phytoplankton biomass, oxygen consumption and nitrification rates, these parameters appeared to stabilize at levels similar to the control ponds. Early season compositional differences in phytoplankton, zooplankton, and bacterial communities were observed. No differences were seen in late-season phytoplankton and bacteria; however, zooplankton biomass tended to be lower in the biosecure pond than in the control ponds throughout the season. Shrimp production in all ponds was greater than 9,000 kg/ha. Production in the single biosecure pond was not a significant outlier compared to production in the triplicate control ponds.     

Effects of Pond Volume Manipulation on Production of Fingerling Largemouth Bass,Micropterus salmoides

Hatchery ponds were manipulated by timing of filling to increase the efficiency of production of fingerling largemouth bass, Micropterus salmoides. The effects on pond productivity of fertilizing with chicken manure versus plant meals (consisting of equal parts by weight of cottonseed meal, alfalfa meal, and wheat shorts) were also examined. When ponds were filled in stages, more favorable water temperatures for largemouth bass were achieved, and desirable dissolved oxygen concentrations were maintained. Chlorophyll a levels and plankton community respiration rates were higher in ponds that were fertilized with the plant meals than in ponds fertilized with chicken manure (25% dry matter). Secchi disk visibility was relatively greater in chicken manure ponds than in ponds fertilized with the plant meals; however all differences were not significant. Zooplankton densities were comparable among treatments. Filling ponds in stages had no significant effects on chlorophyll a, plankton community respiration rate, Secchi disk visibility, or zooplankton abundance and population dynamics. Daily production of largemouth bass was greater in ponds filled in stages and fertilized with plant meals than in other treatment ponds. Yield was highest in stage-filled ponds fertilized with plant meals and lowest in full ponds fertilized with chicken manure. Filling ponds in stages reduced the fertilizer cost per kilogram of largemouth bass by 50% in ponds fertilized with plant meals and by 65% in manure-fertilized ponds.     

枯草芽孢杆菌培育生物絮团对池塘水体浮游生物的影响

为探究枯草芽孢杆菌(Bacillus subtilis)培育生物絮团对浮游生物的影响,以枯草芽孢杆菌作为试验菌种,以养殖池塘水为试验用水,在有机玻璃水族箱(100 cm×60 cm×50 cm)中进行为期40 d的生物絮团培育试验。试验以添加葡萄糖为处理组I,同时添加枯草芽孢杆菌和葡萄糖为处理II组,仅添加枯草芽孢杆菌为处理III组,对照组不添加任何物质。试验过程中每5 d对各组水体取样,对形成的絮团物质进行显微观察,同时对各组水体中浮游生物进行定性和定量分析。结果表明,本试验条件下,处理I组和处理II组在第15天左右形成成熟生物絮团,生物絮团形成前期(试验开始至第15天),生物絮团组(处理I组和处理II组)水体中浮游植物丰度显著高于处理III组和对照组,而絮团形成后期(第15~40天),生物絮团组水体中蓝藻门的微囊藻属(Microcystis)、鞘丝藻属(Lyngbya)和绿藻门的扁藻属(Platymonas)、盘藻属(Gonium)和团藻属(Volvax)的丰度显著低于处理III组和对照组,表明生物絮团的形成前期对浮游植物有明显促作用,生物絮团形成后期对蓝藻门中的微囊藻属、鞘丝藻属和绿藻门的扁藻属、盘藻属和团藻属有明显抑制效果;生物絮团形成后期,生物絮团组水体中轮虫、枝角类和桡足类浮游动物丰度显著高于处理对照III组和对照组,表明生物絮团对轮虫、枝角类和桡足类有明显促进作用。     

Natural food intake by juvenile Arapaima gigas during the grow‐out phase in earthen ponds

In carnivorous fish species, zooplankton is one of the main food items in the early life stages and some fish species continue feeding on such food items further along the life stages even in the farming environment. In this study, the intake of natural food items was assessed in juvenile pirarucu Arapaima gigas reared in earthen ponds. Juvenile pirarucu (12.2 ± 4.32 g and 12.1 ± 1.13 cm) were stocked in fertilized earthen ponds (240 m²). For the analysis of the fish stomach content and plankton in the pond water, the fish and pond water were sampled weekly for 75 days and biweekly until the fish reached a mean weight of 750 g. Although artificial feed was used, pirarucu also ingested the natural food available in the pond water. Among the zooplankton, pirarucu demonstrated feeding preference for cladocerans despite the abundance of rotifers and copepods. Cladocerans were present in more than 80% of the stomach contents of fish up to 300 g and in 65%, 45% and 17% of fish of 301–500 g, 501–700 g and 701–900 g respectively. Copepods were present only in fish up to 500 g at low abundance. High ingestion of insects and plant material was observed in the stomach content of fish of all size classes. The results demonstrate that juvenile pirarucu ingest natural food available in the farming pond and suggests that the adoption of pond fertilization practices may have positive effects on fish growth performance.     

Delayed Feeding of Channel Catfish Fry Stocked in Ponds

We compared production variables between channel catfish, Ictalurus punctatus, nursery ponds fed according to industry standards, that is feeding immediately at stocking, to an alternative practice of delaying feeding for 6 wk after stocking in an effort to utilize natural pond productivity and reduce feed use. Twelve 0.04 ha ponds were fertilized and stocked with swim‐up fry (4–5 d posthatch) at a rate of 10,000/pond (250,000/ha). Ponds were then randomly assigned to either the standard feeding protocol (feeding daily starting immediately at stocking) or an alternative feeding protocol (no feeding until 6 wk post‐stocking). After 18 wk of production, there were no differences in water quality or zooplankton abundance between the two treatments. Fish length was not affected by treatment throughout the study, and survival and total weight harvested were similar. Total kg of feed fed was significantly reduced in the delayed feed treatment, averaging 26 kg/pond less feed fed. If proper fertilization practices are implemented, large numbers of desirable zooplankton for catfish fry culture are attained, and these zooplankton are able to sustain catfish fry stocked up to 250,000/ha. Therefore, no commercial diets are required during the first 6 wk of culture, saving over $95.55/ha in initial feed costs.     

长兴岛沿岸春季和夏季的浮游动物群落结构

2005年8月(夏季)的大、小潮期间和2006年3月(春季)的大、小潮期间对长兴岛沿岸进行了4个航次的浮游生物调查,共检出浮游动物47种,其中春季32种,夏季44种。浮游动物的优势类群为桡足类和浮游幼虫。小拟哲水蚤、双毛纺锤水蚤、拟长腹剑水蚤、无节幼虫为春季优势种。小拟哲水蚤、双毛纺锤水蚤、近缘大眼剑水蚤、桡足类幼体、太平洋纺锤水蚤为夏季优势种。春季浮游动物的丰度、生物量及种类数均低于夏季。小潮期间浮游动物的丰度、生物量高于大潮期间。浮游动物的丰度、生物量及优势种受潮周期的影响。北部沿岸和南部沿岸浮游动物丰度、生物量较高。小型桡足类在长兴岛沿岸浮游动物群落结构中扮演重要角色,长兴岛沿岸浮游动物群落结构较为成熟稳定。     

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.     

Experimental evaluation of inorganic fertilization in larval giant grouper (Epinephelus lanceolatus Bloch) production

A major constraint in successful larviculture of groupers has been the small gape of the larvae and hence the requirement for small prey at first feeding. In this study, we examined how maintaining a phosphate concentration of 100 μg P L^?1 and an inorganic nitrogen (N) level of 700 μg N L^?1 via weekly fertilization with inorganic fertilizers affected phytoplankton, zooplankton and giant grouper larval survival in relation to a control group that was provided with rotifers immediately after larvae hatched. Unicellular algae, zooplankton within the size ranges of 10–50 μm and 50–100 μm and survival of giant grouper larvae were all significantly higher in the fertilized treatment compared with the control. Stomach analysis revealed that ciliates and flagellates were actively consumed by larval fish in the fertilized group, whereas few rotifers were consumed in the control. We conclude that the inorganic fertilization method provides high densities of suitable‐sized prey for larval groupers at the onset of exogenous feeding before they are able to consume larger, commercially available rotifers and copepods.     

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.     

Evaluation of the Ciliated Protozoa,Fabrea salina as a First Food for Larval Red Snapper,Lutjanus campechanus in a Large Scale Rearing Experiment

ABSTRACT

One of the major challenges of culturing of red snapper, Lutjanus campechanus, is providing an appropriate food source at onset of feeding. Ciliates are abundant in marine waters but their significance as a first food for fish larvae is poorly understood as many have no lorica to facilitate their identification in the gut of a larval fish. Fabrea salina is a naked heterotrich ciliate that can be mass cultured at densities up to 84 ± 10 ciliates/mL in 7 days. Its appropriateness as a first food for red snapper larvae was evaluated in a green-water setting using 1-m³ tanks. Larvae were stocked at 10/L, 36 h post-hatch, before first-feeding commenced. Larvae were fed either (1) copepod nauplii, 20–75 μm, only from days 1 to 10; (2) copepod nauplii from days 1 to 10 plus F. salina from days 1 to 5; or, (3) F. salina only from days 1 to 3 plus copepod nauplii from days 4 to 10. Copepod nauplii were added at 2/mL and ciliates were added at 5/mL. Survival after 28 days was 0.28 ± 0.15% for larvae given only copepod nauplii and 2.39 ± 2.75% for those given F. salina and copepod nauplii. Larvae given only F. salina did not survive past 4 days post-stocking. Larvae were more actively feeding in the tanks given F. salina and copepods as first foods with 34.6 ± 8.5% mean daily reduction in copepod nauplii compared to 15.8 ± 16.2% reduction when only nauplii were provided.     

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.     

辽宁省黄海北部沿岸夏季和秋季浮游动物群落结构

2014年8月(夏季)和10月(秋季)对辽宁省黄海北部沿岸海域进行了2个航次的浮游生物调查,共检测出浮游动物35种,其中夏季30种,秋季34种。浮游动物以小型桡足类和浮游幼虫为主。洪氏纺锤水蚤、短角长腹剑水蚤、小拟哲水蚤、近缘大眼剑水蚤、强壮箭虫、异体柱囊虫和双壳类幼体为夏季优势种;洪氏纺锤水蚤、短角长腹剑水蚤、近缘大眼剑水蚤、强壮箭虫、异体柱囊虫、桡足类幼虫、沃氏纺锤水蚤为秋季优势种。夏季浮游动物生物量高于秋季,生物量则低于秋季。季节变化会影响浮游动物的丰度和生物量。辽宁省黄海北部沿岸浮游动物丰度、生物量较高,小型桡足类在黄海北部沿岸浮游动物群落结构中具有重要的作用。     

Effects of Mosquitofish,Gambusia affinis,on Channel Catfish,Ictalurus puncatatus,Production Ponds

Mosquitofish, Gambusia sp., have been spread throughout the world to biologically control mosquitoes. However, the fish has gained a reputation as an invasive species and has been implicated in displacing native aquatic species. Gambusia affinis are native to the southeastern United States and commonly occur in commercial channel catfish, Ictalurus punctatus, production ponds. We investigated effects of mosquitofish presence on zooplankton populations, water quality, disease occurrence, and fish production in experimental ponds. There were no differences between ponds with or without mosquitofish in numbers of calanoid copepods, cyclopoid copepods, total copepods, Bosmina sp., Ceriodaphnia sp., Moina sp., Daphnia sp., or total cladocerans. There were also no differences in copepod and cladoceran sizes. Copepod nauplii were more numerous during the summer months in ponds with mosquitofish. There were no differences in water quality variables (soluble reactive phosphorus, nitrate, nitrite, ammonia, total nitrogen, total phosphorus, pH) or phytoplankton density between ponds stocked with and without mosquitofish. Catfish production and disease occurrence were also similar between ponds with and without mosquitofish. Although mosquitofish may cause problems when stocked outside their native range, there does not appear to be any adverse effects of mosquitofish presence in catfish production ponds.