Rotifer Brachionus Research Articles

Cost of reproduction in selected species of zooplankton (rotifers and cladocerans)

Reproduction is an energetically costly biological process. Among the freshwater zooplankton, rotifers and cladocerans reproduce parthenogenetically and the cost of reproduction can be estimated using the life table data from demographic studies. Reduced probability of future survival or future reproduction as a result of current investment in offspring production (trade-off) is the central theme of the cost hypothesis. Correlations using present reproduction vs. future reproduction (called the reproductive costs) or future survival (called the survival costs) can be used to evaluate the cost hypothesis. In this work sets of correlations were made: (1) between present reproduction (mx) vs. future survival (lx+1, lx+2, lx+3 etc. for the entire lifespan) (survival costs), and (2) present reproduction (mx) vs. future reproduction (mx+1, mx+2, mx+3 etc. for the entire reproductive span) (reproductive costs). These correlations were plotted against the cohort age-classes in order to quantify survival and reproductive costs in rotifers (Asplanchna girodi, Brachionus macracanthus, B. variabilis and Platyias quadricornis) and cladocerans (Ceriodaphnia cornuta – one strain maintained on Chlorella and another strain adapted to Microcystis), Daphnia carinata, D. laevis, Moina macrocopa, Pleuroxus aduncus, Scapholeberis kingi and Simocephalus vetulus). All the tested rotifer species showed negative tendency in correlation coefficients (when the data of current reproduction vs. future reproduction and future survival were plotted) for both reproductive and survival costs. However, from the total survival and reproductive costs derived, 84% of the former and 42% of the latter were statistically significant. In cladocerans about 80% of the costs (correlations between current reproduction vs. future survival or future reproduction) were negative suggesting that present reproduction had negatively affected both the further survival and reproduction of test populations. In terms of statistically significant survival costs, the cladocerans showed a trend slightly lower (72%) but comparable to rotifers. The reproductive costs were significant in 45% cases. In our study, the simple statistical correlations detected the trade-offs between reproduction and survival. Thus, in more than 60% cases of both survival and reproductive costs in zooplankton were negative, and our data supported the cost hypothesis, in the majority of cases where reproduction by zooplankton of a given age class caused reduced survival and reproduction of the next age class.

Environmental Variables and Planktonic Communities in Two Ponds of El Hondo Wetland (SE Spain)

The annual cycle of physical and chemical variables and plankton dynamics was studied in two shallow ponds (East and West Ponds) of the El Hondo wetland, an ecosystem of international importance. Water conductivity increased up to 31-49 mS cm -1 as water level decreased due to high evaporation and minimal water inputs. Initially considered mesohaline, the waters were reclassified as polyhaline during the hot season. EP was subject to successive desiccation-flooding cycles, and flooding of the dried sediment caused the release of high concentrations of nitrogen and phosphorus compounds, which quickly depleted. The algal species composition was typical of eutrophic ecosystems, and the chlorophyll content indicated that EP was eutrophic and WP mesotrophic. Phytoplanktonic species richness and diversity were low in both ponds. Algal assemblages, in terms of biovolume, were mainly dominated by Dinophyceae in EP and by Cryptophyta in WP. The zooplankton community was dominated by Rotifers (Brachionus and Hexarthra), although Copepods and Ciliates were also important. Different water inputs to the ponds, partial drying in EP during the warm season with the subsequent higher increment of salinity, and the presence of dense populations of submerged macrophytes in WP, explain the differences in plankton communities found between the two ponds.

Bioaccumulation of butyltins via an estuarine food chain

An estuarine food chain of threetrophic levels–algae (Platymonas sp.), rotifers (Brachionus plicatilis) and mysids (Neomysis awatschensis Brandt) was setup in laboratory in order to investigate contributionsof water and food to the accumulation of butyltins inupper trophic organisms, as well as to evaluate thelikelihood of biomagnification of butyltins throughthe aquatic food chain. Kinetics of bioaccumulationand depuration of butyltins through the food chainwere studied. Bioconcentration factors of butyltins inthe three organisms were high (103–104).Butyltin burdens in the upper trophic organisms atsteady-state of bioaccumulation by the ingestion oftainted food exceeded those observed by exposure towater only. For total butyltins, food chain transfernumber was 1.44 for algae to rotifers and 0.59 forrotifers to mysids, respectively. Biomagnification wasnot confirmed. It is concluded that whether or notbiomagnification occurs depends not only on theproperty of compounds but also on the organisms involved.

Zooplankton Dynamics in the Hyper-Eutrophic Nakdong River System (Korea) Regulated by an Estuary Dam and Side Channels

Zooplankton in the main channel of the Nakdong River and in three tributaries was sampled from June 1994 to September 1995. Planktonic rotifers (Brachionus spp., Keratella spp., and Polyarthra spp.), cyclopoid nauplii and small cladocerans (Bosmina longirostris) were numerically dominant. There was considerable longitudinal variation of zooplankton biomass in the main channel as well as spatial heterogeneity among the major tributaries. In the middle region of the main channel, between river kilometer (RK) 170 and 150 above the estuary dam, total zooplankton abundance sharply increased from less than 100 ind. L -1 to more than 1,000 ind. L -1 . In a downstream direction toward the estuary dam, phytoplankton biomass increased while total zooplankton biomass decreased. However, as shown by the increasing transport of zooplankton biomass, zooplankton was diluted in the reach of the estuary dam. Advective effects from major tributaries appear to be the contributory factor for the higher zooplankton biomass in the middle region. Overall, rather the external factors (flushing, retention) than internal factors (e.g., phytoplankton) appear to be responsible for changes in zooplankton abundance toward the river mouth.

Nutrient enrichment and zooplankton effects on the phytoplankton community in microcosms from El Andino reservoir (Venezuela)

To quantify the effects of nutrient enrichment (N and P) and zooplankton grazing on the phytoplankton community structure of El Andino reservoir (Venezuela), in situ microcosms were installed for 6–7 days. Microcosms consisted of polyethylene bags (42 cm × 71 cm, non-cylindrical shaped) filled with 10 l of filtered epilimnetic water. Experiments were carried out on a monthly basis from January to December 1993. The lack/addition of nutrients was cross-classified with the absence/presence of zooplankton, resulting in an experimental design of four treatment levels: (1) no nutrient addition, zooplankton absent (C); (2) nutrient addition (150 NH4Cl μmol ml−1 and 10 KH2PO4 μmol ml−1; 1 ml per l of sample), zooplankton absent (N); (3) no nutrient addition, zooplankton present (collected from the reservoir water column using a 6-m vertical tow with a 80-μm plankton net) (Z); and (4) nutrient addition (as in [2]), zooplankton present (as in [3]) (NZ). Treatments were triplicated, and samples were collected at the start and end of each experiment. Significant differences between treatments were determined using a two-way ANOVA at p<0.05. Nutrient enrichment caused an increase in phytoplankton biomass, with the increase of all algal groups, except Pyrrhophyta. In spite of this, relative proportions of Cyanobacteria decreased in most cases. Chlorophyta and Bacillariophyta increased, probably due to their greater competitive abilities for phosphorus. After enrichment, Scenedesmus was the dominant species from January to June, while from July to December, Dactylococcopsis and Lyngbya dominated in the enriched microcosms. Zooplankton affected the phytoplankton community in microcoms through grazing and nutrient (mainly P) regeneration. Cladocerans (Ceriodaphnia cornuta, Moina micrura and Diaphanosoma sp.) mainly grazed on diatoms, although particulate material was present in almost all the gut contents analyzed. Particulate material probably consisted of micro-algae, detritus, bacteria, triturated algae and mineral particles. Ostracoda mainly fed on Peridinium and particulate material, whereas Thermocyclops sp. and rotifers (Brachionus spp. and Keratella spp.) mainly ingested particulate material. On the other hand, zooplankton excretion caused a slight increase in phytoplankton biomass and P concentrations in microcosms with the animals present. The effects of nutrient and zooplankton did not interact in most cases. Experimental results suggest that, at the initial stages of a eutrophication process, phytoplankton could increase their abundance and biomass, but might not change its community structure. Since there was a strong correlation between phosphorus and chlorophyll-a (bottom-up control), it is suggested that eutrophication could be avoided by controlling P input to the reservoir.

Development of larval diets for milkfish (Chanos chanos)

This study aimed to develop nutritionally balanced and cost-effective processed diets for milkfish larvae (Chanos chanos Forsskal). Two larval diets (feed A and feed B) were formulated and prepared to contain 45%| protein and 10%| lipid. Several larval diet preparations were tried such as microbound/ unpelleted (freeze-dried), microbound/pelleted (oven-dried) and microbound/flaked (drum-dried) and assessed in terms of feed particle size and buoyancy, water stability and feed acceptability. The preparation that gave the best particle size and buoyancy as well as good water stability was prepared as the microbound diet (using K-carrageenan as a binder) and flaked using a drum drier. A series of feeding experiments were conducted to determine the growth and survival of milkfish larvae reared on various feeding schemes using these processed larval diets which were fed either solely or in combination with live feed. Larvae in control treatments were reared on live foods such as Brachionus plicatilis and Artemia nauplii. Larvae were observed to ingest the diets, indicating that the feeds had suitable physical characteristics and were attractive to the larvae. The overall results of the feeding trials showed that the artificial diets could be fed to milkfish larvae in combination with Brachionus rotifers starting on day 2 or day 8, and could be fed alone starting from day 15. These promising results would reduce the dependence of milkfish larvae on live feed and would have significant economic benefits in the form of simplified milkfish hatchery procedures.

The longitudinal distribution and community dynamics of zooplankton in a regulated large river: a case study of the Nakdong River (Korea)

The longitudinal distribution and seasonal dynamics of zooplankton were examined along a 200-km section of the middle to lower Nakdong River, Korea. Zooplankton was sampled twice a month from January 1995 to December 1997 at five sites in the main river channel. There was considerable longitudinal variation in total zooplankton abundance (ANOVA, p < 0.001). All major zooplankton groups (rotifers, cladocerans, copepodids and nauplii) increased significantly with distance downstream along the river. There also were statistically significant seasonal differences in zooplankton abundance at the sampling sites (ANOVA, p < 0.01). Zooplankton abundance was high in spring and fall and low in summer and winter. The seasonal pattern of rotifers was similar to that of total zooplankton. This reflected the fact that rotifers (Brachionus calyciflorus, B. rubens, Keratella cochlearis and Polyarthra spp.) strongly dominated the zooplankton community at all locations. Among the macrozooplankton, small-bodied cladocerans (e.g. Bosmina spp.) dominated; the abundance of large-bodied cladocerans (e.g. Daphnia) was negligible (0–5 ind. l−1). Among the environmental variables considered, partial residence time seemed to play the most important role in determining characteristics of the river zooplankton community.

Colonization of the gut in first feeding turbot by bacterial strains added to the water or bioencapsulated in rotifers

Two bacterial strains, 4:44 and PB52, isolated from turbot(Scophthalmus maximus L.) were used during a first feedingexperiment with turbot larvae. Bacteria were either added directly tothe water on the day of hatching of the larvae (day 0), orbioencapsulated in rotifers (Brachionus plicatilis) distributedon day 2 after hatching. The two bacterial strains were found to bepresent in the water of the rearing tanks throughout the experiment. Theaddition of bacteria influenced the species-composition of themicroflora associated with intensively produced rotifers added to thetanks, and resulted in colonization of the gut of the larvae by theadded bacterial strains. The strain 4:44 showed a peak on day 9 afterhatching, and reached a mean(sem) of 2.5(1.4) × 104bacteria per larva, when added in a mixture with PB52, and 0.4(0.1)× 104 bacteria per larva, when added alone. The strainPB52, on day 12 after hatching, reached 5.2(1.5) × 104bacteria per larva when added in a mixture with strain 4:44, and12.5(0.7) × 104 bacteria per larva, when added alone.The added bacteria colonized the gut turbot larvae, whereas thebacterial land, the survival and growth of the larvae were in most casesnot influenced in a negative way by the addition of bacteria.

Nutrient enrichment and zooplankton effects on the phytoplankton community in microcosms from El Andino reservoir (Venezuela)

To quantify the effects of nutrient enrichment (N and P) and zooplankton grazing on the phytoplankton community structure of El Andino reservoir (Venezuela), in situ microcosms were installed for 6–7 days. Microcosms consisted of polyethylene bags (42 cm × 71 cm, non-cylindrical shaped) filled with 10 l of filtered epilimnetic water. Experiments were carried out on a monthly basis from January to December 1993. The lack/addition of nutrients was cross-classified with the absence/presence of zooplankton, resulting in an experimental design of four treatment levels: (1) no nutrient addition, zooplankton absent (C); (2) nutrient addition (150 NH4Cl μmol ml−1 and 10 KH2PO4 μmol ml−1; 1 ml per l of sample), zooplankton absent (N); (3) no nutrient addition, zooplankton present (collected from the reservoir water column using a 6-m vertical tow with a 80-μm plankton net) (Z); and (4) nutrient addition (as in [2]), zooplankton present (as in [3]) (NZ). Treatments were triplicated, and samples were collected at the start and end of each experiment. Significant differences between treatments were determined using a two-way ANOVA at p<0.05. Nutrient enrichment caused an increase in phytoplankton biomass, with the increase of all algal groups, except Pyrrhophyta. In spite of this, relative proportions of Cyanobacteria decreased in most cases. Chlorophyta and Bacillariophyta increased, probably due to their greater competitive abilities for phosphorus. After enrichment, Scenedesmus was the dominant species from January to June, while from July to December, Dactylococcopsis and Lyngbya dominated in the enriched microcosms. Zooplankton affected the phytoplankton community in microcoms through grazing and nutrient (mainly P) regeneration. Cladocerans (Ceriodaphnia cornuta, Moina micrura and Diaphanosoma sp.) mainly grazed on diatoms, although particulate material was present in almost all the gut contents analyzed. Particulate material probably consisted of micro-algae, detritus, bacteria, triturated algae and mineral particles. Ostracoda mainly fed on Peridinium and particulate material, whereas Thermocyclops sp. and rotifers (Brachionus spp. and Keratella spp.) mainly ingested particulate material. On the other hand, zooplankton excretion caused a slight increase in phytoplankton biomass and P concentrations in microcosms with the animals present. The effects of nutrient and zooplankton did not interact in most cases. Experimental results suggest that, at the initial stages of a eutrophication process, phytoplankton could increase their abundance and biomass, but might not change its community structure. Since there was a strong correlation between phosphorus and chlorophyll-a (bottom-up control), it is suggested that eutrophication could be avoided by controlling P input to the reservoir.

Temporal variation in plankton assemblages and physicochemistry of Devils Lake, North Dakota

Seasonal and annual variation in biomass and structure of algal assemblages of hyposaline Devils Lake were examined in relation to turbidity, ambient concentrations of major ions, trace elements and nutrients, and the standing crop of herbivores. Lake level declined during the early years of study, but rose markedly in subsequent years as historically large volumes of water flowed into this hydrologically-closed basin. Winter algal assemblages were dominated (in biomass) most years by small, non-motile chlorophytes ( Choricystis minor, Kirchneriella lunaris or Dunaliella sp.), or Euglena sp. in the most saline sub-basin. Spring assemblages were dominated by diatoms (Stephanodiscus cf. minutulus, Surirella peisonis, Cyclotella meneghiniana and Entomoneis paludosa were especially prominent) or chlorophytes ( C. minor) until the lake level rose. C. minor abundances then declined in spring assemblages and diatoms ( Stephanodiscus cf. agassizensis and S. niagarae; E. paludosa in the more saline sub-basins) dominated. The potential for nitrogen-deficient conditions for phytoplankton growth was evidenced most summers and early autumns by consistently high concentrations of reactive-P relative to inorganic-N and blooms of the N-fixing cyanophyte Aphanizomenon flos-aquae; Microcystis aeruginosa typically was a co-dominant (>30% of biomass) in these assemblages. Pulses of diatoms ( S. cf. agassizensis and C. meneghiniana) occurred in summers following unusually prolonged periods of calm weather or large water inflows. Physical (irradiance, turbulence) and chemical (major nutrients) variables were the primary factors associated with phytoplankton growth. Transparency and major nutrient concentrations accounted for more of the annual variation in phytoplankton structure than did salinity. Seasonal abundance patterns of the dominant zooplankton (the copepod Diaptomus sicilis; the cladocerans Ceriodaphnia quadrangula, Chydorus sphaericus, Daphnia pulex and Diaphanosoma birgei; and the rotifers Brachionus spp., Filinia longiseta, Keratella cochlearis and K. quadrata) also indicated variation in algal populations related to grazing.

Toxicological analysis of the marine cyanobacterium Nodularia harveyana

Nodularia harveyana, a dinitrogen-fixing cyanobacterial isolate from the Mediteranean Sea, grown in an outdoor photobioreactor, was assayed for its bioactive compounds. The active substance(s) were lypophilic and showed strong allelopathic actvity against other axenic cyanobacteria, antibiotic activity against Gram-positive pathogenic bacteria and antifungal activity against two plant pathogens. The extracts were toxic (LC50 at 30 μL) for grazers such as a rotifer (Brachionus calyciflorus) and a crustacean (Thamnocephalus platyurus).

Somatic and population growth in selected cladoceran and rotifer species offered the cyanobacterium it Microcystis aeruginosa as food

The ability of cladocerans and rotifers to utilise the cyanobacterium Microcystis aeruginosa was tested by comparing the somatic and population growth in cultures using Chlorella and Microcystis as food types. Five species of cladocerans (Ceriodaphnia cornuta, Scapholeberis kingi, Moina macrocopa, Daphnia carinata, Simocephalus vetulus) and two species of rotifers (Brachionus calyciflorus, Hexarthra mira) were used in this study. In order to exclude the possibility of poor utilisation of Microcystis due to mechanical interference, single cells of Microcystis, (obtained by sonicating large colonies) were also offered. Experiments were done at 20 °Cs and 30 °C . In all the treatments tested, the population growth rate per day of the cladocerans ranged from -0.715 to 0.612 and that of the rotifers from -1.15 to 0.781. While C. cornuta, S. kingi and S. vetulus could utilise Microcystis, M. macrocopa and D. carinata were extremely susceptible to its toxins. The ability of the cladoceran populations to grow on Microcystis single cells was not related to the body length or gut length alone but to their ratio. The toxic effects of Microcystis were mitigated at the higher temperature. A strain of C. cornuta, collected from a Microcystis-dominated lake, had a higher growth rate on the toxic cyanobacteria suggesting that the tolerance to Microcystis could be a heritable trait. Of the two rotifer species, only H. mira survived and reproduced in some treatments of Microcystis.

A method for the early assessment of the quality of turbot larvae

The bacterial environment should be taken into account for assessing the quality of fish larvae, besides biochemical and developmental criteria. Detrimental effects of associated flora have been observed on the survival rates of larvae (e.g. Nicolas et al., 1989), and experimental infections were performed on fish larvae by introducing the pathogen either directly into the rearing medium or into live food organisms (e.g. Kusuda et ai, 1986). A challenge test was used for assessing the effect of a food additive on the ability of turbot (Scophthalmus maximus) larvae to resist infection, but that required rearing the larvae separately (Gatesoupe, 1993). Bergh et al. (1992) have proposed an infection test with transfer of eggs into polystyrene dishes, but it was not convenient for larvae with exogenous food source. The present paper was an attempt to develop a new test with transfer of larvae after feeding. Then this test was inserted into a simple survey of the quality of turbot larvae, with a view to drawing up relations between rearing success, associated bacteria and resistance against pathogens. For this purpose, seven batches of larvae were successively reared in 150 1 cylindrical tanks with conical bottoms from day 1 after hatching until day 10. Three tanks were used for batches 1, 3, 5 and 6, while five tanks were used for batches 4 and 7. The larvae of batch 2 were reared in one tank. The rearing temperature was gradually increased from 14 °C to 18 °C by day 5. The salinity was 35%. For feeding the larvae, rotifers (Brachionus plicatilis) were cultured in seawater according to the method already described (Gatesoupe, 1990). The rotifer diet was made up of baker's years, menhaden (Breuoortia tyrannus) oi l (Sigma F8020), soybean lecithin, DL-a-tocopherol (USB), and vitamin premix (Spyridakis et ai, 1988), at the daily rates of 60.8, 7.7, 0.7, 0.015, and 0.7 mg r1, respectively, on a dry matter basis. The larvae were fed with the rotifers from day 3 to day 9, at the daily rates of 20, 50, 75, 100, 150, 200, and 250 rotifers per initial larva, corresponding to the seven consecutive days of feeding. Each day, the rotifers were transferred from their culture medium into clean seawater tanks (200 rotifers m l 1 ) , where they were enriched with spray-dried fish autolysate, menhaden oi l , soybean lecithin, and DL-a-tocopherol, at the rates of 15, 7.7, 0.7, and 0.015 mg T 1 , respectively, on a dry matter basis. The rotifers were continuously distributed to turbot with a peristaltic pump, the flow rate of which was adjusted so that the whole volume was carried through in 24 h. At day 10, the survivors were counted and 30 fish were sampled in each tank,

Chemical suppression of feeding in larval weakfish (Cynoscion regalis) by trochophores of the serpulid polychaeteHydroides dianthus

We studied the effect of exudates from trochophore larvae of the polychaeteHydroides dianthus on feeding in larval weakfish (Cynoscion regalis). Laboratory prey consisted ofH. dianthus trochophores and/or comparably sized rotifers (Brachionus plicatilis). When experiments were conducted in filtered seawater, ingestion of rotifers was always greater than ingestion of trochophores. However, consumption of rotifers was depressed when water fromH. dianthus cultures (=trochophore water) was the experimental medium. The same effect was noted whether we added trochophore water from polychaete cultures that were two or five days postfertilization. However, no effect was noted when we used water from rotifer cultures. We concluded thatH. dianthus trochophores release a water-soluble compound that inhibits feeding in weakfish larvae.

Feeding, Growth, and Survival of Atlantic Cod (Gadus morhua) Larvae Reared in Replicate Plastic Enclosures

Feeding, growth, and survival of Atlantic cod (Gadus morhua) larvae were examined during their first 2 mo of life. The experiment was carried out in eight plastic enclosures of 10 m3 volume each. Larval cod, at an initial stocking density of 10 larvae/L, were fed rotifers (Brachionus plicatilis) and natural zooplankton collected from the sea. The enclosures replicated well with regard to hydrography, feeding conditions, and larval growth and survival. Larval mortality was low during the first month, with a mean mortality rate (Z) of 0.02/d. Growth, however, was very slow and mortality increased significantly after about 4 wk, possibly due to starvation. Brachionus plicatilis dominated the gut content during the first 3–4 wk. The zooplankton concentration averaged 15–80 rotifers/L during the first 2 wk, which seemed to be insufficient under the present rearing conditions. Most of the larvae were distributed in the upper parts of the rearing enclosures, while rotifers were distributed deeper. This, together with the high larval density, inadequate rotifer enrichment, and low temperature probably amplified the unfavourable feeding conditions.

High incorporation of esential fatty acids by the Rotifer Brachionus plicatilis fed on the Prymnesiophyte Alga Pavlova lutheri

The lipid and fatty acid compositions of rotifers (Brachionus plicatilis) fed on yeast or on the unicellular prymnesiophyte Pavlova lutheri, an alga commonly used in Australian hatcheries, were compared by TLC-FID, GC and GC-MS. Significantly higher relative proportions of energy-rich triacylglycerol were present in the Pavlova-fed rotifers than in the yeast-fed animals, and total lipid content reached a maximum between 12 and 24 h. High incorporation of the essential fatty acids eicosapentaenoic acid (EPA; 20: 5ω3) and docosahexaenoic acid (DHA; 22:6ω3) occurred in the Pavlova-fed rotifers. EPA and DHA content was 11.6% of total fatty acids after 3 h of feeding and reached 20 and 23% after 24 and 48 h respectively. The proportion of essential fatty acids in rotifers fed Pavlova compares very favourably with data obtained by overseas workers using a variety of microalgae and dietary supplements. On the basis of fatty acid composition alone, these results confirm the suitability of P. lutheri as a feedstock for Australian mariculture operations.

Laboratory culture and feeding of the hydromedusa Cladonema californicum Hyman (Anthomedusa: Cladonemidae)

This report describes culture, growth and feeding characteristics of the medusa stage of Cladonema californicum Hyman. Polyps were grown in the laboratory in order to collect undamaged medusae. Budding of medusae from polyps occurs predominantly during the light hours of a 12:12 light:dark cycle. Growth of medusae was most rapid when fed Artemia sp. nauplii; lower growth rates were associated with the harpacticoid copepod Tisbe sp. and the rotifer Brachionus. Ingestion rates of unstarved medusae are dependent upon bell diameter and, at all but the highest prey concentrations (300 prey/1), C. californicum medusae ingest prey at rates linearly related to prey concentration.

Growth of Juvenile Barramundi (Lates calcarifer) on Dry Feeds

Abstract A suitable feeding program for juvenile barramundi (Lates calcarifer) includes rotifers (Brachionus plicatilis) and Artemia sp. nauplii for larvae, followed by dry starter and production feeds for juveniles. When 9–62-g barramundi were fed similar diets containing 9.3 and 12.9% fat, daily ration (2.4%) and growth (2.5%) were similar, but feed conversion ([dry weight of feed eaten]! [wet fish weight gained]: 0.93 and 1.01 for the low- and high-fat diets, respectively) was significantly lower (P < 0.05) with 12.9% fat. When 15–71-g barramundi were fed a series of six dry diets, the feed containing the most fish meal (60%) and fat (16.9%) produced the best feed conversion (0.89); however, a diet containing 20% fish meal and 13.4% fat gave practically the same results. When 74–150-g fish were fed one or two meals a day, daily growth was similar (1.7%), but daily ration (1.9% for one meal and 2.0% for two meals) and feed conversion (1.09 and 1.21, respectively) were significantly lower (P < 0.05) with...

Selenium uptake and transfer in an aquatic food chain and its effects on fathead minnow larvae

The transfer of Se (Na2SeO4) was followed through a laboratory food chain (wateralgae-rotifer-larval fish) and its effect on larval fathead minnows (Pimephales promelas). Selenium transfer between algae (Chlorella pyrenoidosa) and rotifers (Brachionus calyciflorus) was a function of time and food availability. Selenium concentrations in the rotifers ranged from 46 to 91Μg Se · g−1 dry weight after 5 hr of feeding. Selenium concentrations (±SD) in larval fish reached 61.1±1.1 Μg Se · g−1 dry weight for 9 day-old larvae and 51.7+1.6 Μg Se · g−1 for 17 day-old larvae after 7 and 9 days of feeding with Se-contaminated rotifers, respectively. Final dry weights of larvae fed Se-contaminated rotifers were significantly lower than those of controls, although acute toxicity (mortality) was not demonstrated. The biological halflife of food-derived Se in the larvae was 28 days.

A Flow-Through System for Rearing Flatfish Through Metamorphosis

Abstract The details of a flow-through system developed at the New England Aquarium for rearing starry flounders (Platichthys stellatus) through metamorphosis are presented to provide a comparison with closed systems, and an abbreviated manual for rearing of flatfish and their food organisms. The flow-through system allowed rapid response to changes in water quality and permitted the use of very high food concentrations. The success of the operation also depended on the production of up to 106 rotifers (Brachionus plicatilis) per day, which depended on the production of at least 20 liters per day of algal (Dunaliella sp.) culture. Up to 682 fish were reared through metamorphosis per 19-liter tank.