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The study was conducted to assess the community structure of planktonic rotifers and their relation to the environmental impact of Nile tilapia, Oreochromis niloticus (Linaeus, 1758), aquaculture activities (ponds and net-tanks), associated with a Neotropical semiarid reservoir in Brazil. Our hypothesis was that the ecological attributes of the rotifer community were different when considering the influence of fish aquaculture activities. We identified 28 species, with 10 species from the Brachionidae family. The average density and diversity index of rotifers were higher in reservoir stations, with mean values in the ponds approximately 50% lower than those of the reservoir. The microphagous species dominated during all the time, while the raptorial species were accidental in all studied environments. The ponds were represented by four significant indicator species: Brachionus caudatus, B. leydigi, Dicranophoroides caudatus and Testudinella patina and the reservoir by three: B. falcatus, B. havanaensis and Conochilus dossuarius. In general, nine species were significantly associated with some categories of environmental conditions, such as high or low turbidity and low values of conductivity and TDS. Four of the five best bioindicator species belonged to the microphagous genus Brachionus. B. havanaensis indicated five environmental conditions (IndVal > 93.1%), and it appeared to be a key species in this Neotropical semiarid reservoir influenced by aquaculture activities. The dominance of microphagous rotifers suggests a functional redundancy of species in the studied environments. We found that these systems and their management affected the planktonic rotifer community in this region of Brazil by increasing the species richness.

To investigate the dietary effect of taurine on the larval stage of tuna species, Pacific bluefin tuna (PBF) and yellowfin tuna (YFT), larvae were reared until 16 days after hatching (dAH) and 14 dAH, respectively, and replicate samples were fed either non-taurine-enriched rotifers (T-0) or rotifers enriched with 800 mg taurine L−1 (T-800). Most PBF and YFT larvae were at the preflexion stage until 7 and 8 dAH, and there were no differences in the growth performance and total protein content of larvae between the T-0 and T-800 groups (t-test; P > 0.05). Thereafter, however, for larvae of both species, these parameters in the T-800 group significantly increased with enhanced notochord development compared to those in T-0 group (t-test; P

The larval rearing performance of California yellowtail (Seriola lalandi) and white seabass (Atractoscion nobilis) was compared between larvae fed taurine-supplemented rotifers (Brachionus plicatilis) and Artemia (Artemia franciscana) and control groups fed live feeds with no taurine enhancement. Results from the S. lalandi trial demonstrated that when fed taurine-supplemented rotifers, survival was significantly higher than the control group (20.1% vs. 9.1%, P

The aim of this study was to evaluate the effect of the addition of Navicula spp. and Brachionus plicatilis on water quality and growth of postlarvae shrimp Litopenaeus vannamei reared in a biofloc system. Four treatments were considered: a control (biofloc system – BFT); BFT with the addition of Navicula spp. (BFT-N); BFT with the addition of Brachionus plicatilis (BFT-B) and BFT with the addition of Navicula spp. and Brachionus plicatilis (BFT-NB), each in triplicate. Shrimp (16.2 ± 0.03 mg) were stocked at a density of 2500 shrimp m−3 and plankton were added on days 1, 5, 10, 15, 20, 25 and 30 at a density of 5 × 104 cells mL−1 (Navicula spp.) and 30 organisms L−1 (Brachionus plicatilis). The shrimp were fed a formulated feed in four daily rations composed of 40% crude protein and 8% lipids. Significant differences between treatments were observed for final weight, yield, feed conversion ratio, specific growth rate, protein efficiency ratio and protein content of the shrimp. The combined plankton addition of Navicula spp. and B. plicatilis had better performance parameters, indicating their benefit as natural food sources for postlarvae L. vannamei in biofloc systems.

Harpacticoid copepods are being considered as alternative candidates for live feed in aquaculture, but their benthic affinity may pose problems for pelagic fish larvae. We compared the swimming behaviour and feeding incidence of herring larvae (Clupea harengus) in the presence of harpacticoid copepods (Tachidius discipes) and rotifers (Brachionus plicatilis). Additionally, we provided T. discipes via a floating sieve to improve the prey availability. The comparison was performed at 5 and 10 days post hatch (dph) via 2D-video observations. Quantitative analyses of larval trajectories allowed the estimation of feeding behaviour through a series of indicators: swimming speed, straightness of trajectories, turning angles and swimming activities (break, sink, slow, normal, fast). The outcomes highlighted that the prey type had no significant effect on swimming speed or straightness of the swimming path. However, at 10 dph directly copepod-fed larvae spent less time in slow but more time in the normal swimming-state than rotifer-fed larvae and larvae fed with Tachidius via sieve. This suggests higher energy expenditure of directly copepod-fed larvae. Moreover, the feeding incidence was higher in larvae fed with Tachidius via sieve than directly Tachidius-fed larvae. Thus, providing harpacticoid copepods via a floating sieve can improve the rearing of marine fish larvae.

A strain of the lineage Brachionus ‘Nevada’ was batch cultured with two diets, differing in biochemical composition: baker’s yeast (treatment 1), which has higher protein:lipid ratio compared with CULTURE SELCO (treatment 2). The biochemical composition (DNA, RNA, lipid, protein content) and fatty acid profile of rotifers of both treatments was analysed and related to previously published population structure data. CULTURE SELCO-fed rotifers showed higher DNA, RNA, lipid, n-3 highly unsaturated fatty acids (HUFA) average content, compared with yeast-fed rotifers, which had higher protein content. Rotifer lipid content showed significant diurnal variation in yeast-fed rotifers. Rotifer lipid and n-3 HUFA content was associated with reproductive output. DNA and RNA content was related to embryonic development while protein content, to somatic growth and mixis. The saturated and monounsaturated fatty acid rotifer content was stable irrespective of feed, in contrast to eicosapentanoic acid (EPA) and DHA. The levels of AA were similar in both rotifer populations, but those of EPA and docosahexaenoic acid (DHA) were about half in yeast-fed compared with CULTURE SELCO-fed rotifers. CULTURE SELCO resulted in a temporally stable rotifer lipid profile and a better enriched parthenogenetic population.

Unidirectional mass truncation selection for small-sized cysts was carried out on brine shrimp (Artemia franciscana Kellogg 1906), Vinh Chau strain, Vietnam, through cyst sieving and then culturing the selected individuals (

This study compared the efficacy of four products that are commonly used in hatchery for nutritional enhancement of rotifer Brachionus plicatilis as the starter food for yellowtail kingfish Seriola lalandi larvae. This experiment consisted of one fresh algae and three enrichment products: (1) Fresh algae were a mixture of Nannochloropsis and Isochrysis at 2:1 on a cell concentration basis; (2) S.presso, (Selco S.presso ® , INVE Aquaculture); (3) Algamac 3050 ® (Aquafauna, USA); (4) Nutrokol ® (NutraKol, Australia). Survival rates of the fish fed rotifers enriched with fresh microalgae (40.69%) and S.presso (31.21%) were higher than those fed Algamac 3050 (10.31%). On 3 day post hatch (DPH), fish feeding incidence in the fresh algae treatment was significantly higher than that in other treatments. On 6 DPH, fish showed the lowest feeding incidence in the Algamac 3050 treatment. The methods of enrichment did not affect total lipid levels in either rotifer or fish larvae, but Algamac 3050 enrichment achieved the highest DHA/EPA ratio and lowest EPA/ARA ratio in both rotifers and fish larvae. This study indicates that fresh algae can be replaced by S.presso, but Algamac 3050 is not as good as other formula for rotifer enrichment in rearing yellowtail kingfish larvae in this system.

Due to growing interest in bacterial probiotic incorporation within juvenile marine finfish production, multiple commercial products are currently available. The following trial was conducted to test the effect of incorporation of a commercially available Bacillus spp. probiotic blend (EcoAqua) on population growth dynamics of the rotifer Brachionus plicatilis. Incorporation consisted of 0.1 mL L−1 daily probiotic additions directly to rotifer cultures and 0.1 μL mL−1 additions to feed mixtures during preparation. Probiotic-treated cultures’ daily mean populations were found to be significantly greater (Pα(2),4,4

One of the major challenges in marine fish culture is how to provide live food of adequate size and nutritional quality for first-feeding larvae. Commonly used live food organisms, rotifers and brine shrimp, may not always be the best option. To determine the suitability of different zooplankton in the larviculture of Elacatinus figaro, three diets were tested: RE – rotifers Brachionus sp. (10 ind mL−1)+ciliate Euplotes sp. (10 ind mL−1), enriched with fatty acids; RC – enriched rotifers (10 ind mL−1)+wild copepod nauplii (10 ind mL−1); and R – enriched rotifers (20 ind mL−1). Survival rates were estimated 10 days after hatch (DAH) for the three test groups, and growth rates were evaluated for RE and R at 10 and 20 DAH. Although survival rate was numerically higher for the RC diet (41.1±14.2%), no significant difference was detected between groups fed RE (20.5±18.1%), RC or R (32.1±16.5%). At 10 DAH, the growth rate was significantly higher in RC (5.7±0.6 mm) than in R (4.6±0.5 mm), a trend that was also observed at 20 DAH for RC (8.6±0.5 mm) and R (5.8±0.7 mm) (P

This study describes the rotifer mass culture protocol developed at the Institute of Aquaculture (HCMR) in Crete. Rotifers were cultured semi-continuously at a density of 257.6 ± 2.6 ind. mL−1, with a daily dilution rate of 25%. An automatic feeder was used to administer dry feed (Selco Sparkle®) every 10 min. A number of factors were investigated so as to provide an in-depth analysis of the advantages and disadvantages of the two systems, especially when compared with traditional protocols such as batch culture. The use of these two systems resulted in a culture of considerable duration (41 days) and daily yield (0.21 ± 0.01 ind. 106 day−1 L−1), using exclusively dry feed. Both systems can be easily applied in hatcheries, requiring few modifications on existing protocols and contribute to a stable and predictable production. Further improvements include manipulation of the dilution rate, food ration, culture volume and duration, as well as choice of a phytoplankton-based diet.

The rotifer Brachionus plicatilis is one of the most important live-feed organisms used in the larval culture of marine fish. Bioencapsulation of florfenicol in rotifers was investigated by delivering it directly to the organisms as particles and the doses ranged from 50 to 1000 mg L⁻¹. Analysis of the florfenicol concentrations in rotifers was performed using high-performance liquid chromatography. The uptake increased with the dose and the enrichment time, and the highest concentration achieved in this study, 1.25 ng rotifer⁻¹, was obtained using a dose of 1000 mg L⁻¹ and 150 min of enrichment. The optimal time for satisfactory enrichment of rotifers with florfenicol was found to be dose dependent and ranged from 30 to 120 min for doses between 400 and 800 mg L⁻¹. The parameters affecting the concentrations achieved in rotifers were the size of the florfenicol particles, enrichment time and dose.

The growth potential of cod larvae is not fully achieved when rotifers (Brachionus spp.) are used as live feed. In this experiment, we studied the effect of natural zooplankton (mainly copepods) on the growth of cod (Gadus morhua L.) larvae reared in intensive systems. Using a growth model developed for cod larvae, the growth rates observed could be evaluated and compared with growth rates reported previously. The cod larvae showed optimal growth rates until age 19 days post hatch (DPH) when they reached 9.77 ± 0.25 mm standard length (SL). Early weaning (20–25 DPH) resulted in significantly longer larvae at age 30 DPH compared with late weaning (25–32 DPH); however, in this period, the zooplankton concentrations were low. The experimental larvae showed considerably higher growth rates compared with rotifer (Brachionus spp.)-reared cod larvae in previous experiments. The nutritional composition of cod larvae was analysed and compared with published results on rotifer-reared larvae. The levels of iodine, manganese, selenium and n-3 PUFA were considerably higher in larvae fed copepods compared with larvae fed rotifers. The differences in nutritional status may well explain the differences in growth observed between copepod and rotifer-reared larvae.

The rotifer Brachionus plicatilis is an important com-ponentofaquacultureasa larval feed. Itstaxonomicstatus has been recently re-de¢nedasa species com-plex, consisting of at least 14 new species/lineages.ThisstudydealswiththelineageBrachionus‘Nevada’,which has been shown to occur in European hatch-eries. Astrainof B.‘Nevada’was mass culturedusingtwocommonlyappliedfeedingregimesandanalysedintermsofitsmorphometry.Anewformulawaspro-posed for the calculation of volume, which can beused as an index of adequacy of rotifers as feed for¢sh larvae.The results wererelatedtolife cycle para-meters. The pre-reproductive and reproductivephases were divided into distinct size groups. Diier-ences were also found betweenthe two diets in mor-phometry and demography. Rotifers of a larger size(yeast-based diet) showed a lower growth rate and alonger reproductive period, lifespan and mean gen-eration time compared with smaller-sized rotifers(CultureSelco s -baseddiet). Interms of loricalength,the present study’s strain of B. ‘Nevada’ (238.5mm)was intermediate between values reported for Bra-chionus ibericus (193.5 mm) and B. plicatilis sensustricto(299mm).Keywords: aquaculture,culturedorganisms,hatch-eries,morphometry,masscultureIntroductionThe monogonont rotifer Brachionus plicatilis hasbeenthesubjectofextensiveresearchduetoitswide-spread use in aquaculture (Lubzens, Zmora & Barr2001).This rotifer is mass cultured in order to be of-feredas feed during the ¢rst10^30 days after mouthopeningof¢sh larvae. Improvingthee⁄ciencyof ro-tifer mass cultures poses a theoretical challenge forscientistsandaneconomical bottleneck foraquacul-turists. Ittherefore becomes clear that this organismis ofconsiderablecommercialandscienti¢cinterest.The research relating to this species is hamperedby the fact that its taxonomy is not clear. In the last15 years, this rotifer has been divided into diierentmorphotypes (large and small) (Fu, Hirayama & Nat-sukari1991),species(Segers1995;Ciros-Pe¤rez,Go¤mez& Serra 2001) and, most recently, into an additionalarrayofgeneticallydivergentlineages(Go¤mez,Serra,Carvalho & Lunt 2002; Suatoni,Vicario, Rice, Snell C Fontaneto et al.2007).Brachionusrotundiformisrepresentsthesmallmorpho-type(SS-type)(Ciros-Pe¤rez,Go¤mez etal.2001)(Table1).Morphological, ecological and physiological infor-mationon B. plicatiliss.l. has to be revised inviewof

A feeding experiment was conducted to evaluate the effect of rotifers (Brachionus plicatilis) and Artemia sp. enriched differently on early growth, survival and lipid class composition of Atlantic cod larvae (Gadus morhua). Rotifers enrichments tested were: (1) AlgaMac 2000®, (2) AquaGrow® Advantage and (3) a combination of Pavlova sp. paste and AlgaMac 2000®. The same treatments were tested with Artemia as well as a combination of DC DHA Selco® and AlgaMac 2000® as a fourth treatment. After rotifer feeding, the larvae from treatment 3 [1.50 ± 0.11 mg dry weight (dw)] were significantly heavier than larvae from treatment 2 (1.03 ± 0.04 mg dw). After feeding Artemia, the larvae from treatment 1 were significantly heavier (12.06 ± 2.54 mg dw) than those from treatments 3 (6.5 ± 0.73 mg dw) and 4 (5.31 ± 1.01 mg dw). Treatment 3 resulted in the best survival through the 59 days of larviculture. After rotifer feeding, high larval concentrations of docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), arachidonic acid (AA) and ω6 docosapentaenoic acid (ω6DPA) could be linked to better larval growth and survival while after feeding Artemia, high larval DHA/EPA ratios (~3) and high DPA/AA ratios (>1) could be linked to better survival.

Two experiments were carried out to investigate the effects of docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA) and arachidonic acid (ARA) levels in rotifers (Brachionus plicatilis) and Artemia on the survival, development and metamorphosis of mud crab Scylla paramamosain larvae. Five different lipid emulsions, varying in the level of total n-3 and n-6 highly unsaturated fatty acids (HUFA), DHA, EPA and ARA were used to manipulate the fatty acid profile of the live food. Fatty acid profiles of the live food and crab larvae at zoea one, three and five stages were analysed to study the HUFA uptake by the larvae. The fatty acid content of the live food affected the fatty acid profiles of the crab larvae. In both experiments, the survival rate in the zoeal stages was not statistically different among treatments. However, larval development rate and metamorphosis success were affected by the dietary treatments. In this respect, the DHA/EPA ratio in the live food seems to be a key factor. Enrichment emulsions with a very high (50%) total HUFA content but a low DHA/EPA ratio (0.6), or zero total HUFA content caused developmental retardation and/or metamorphosis failure. An emulsion with a moderate total HUFA (30%) and a high DHA/EPA ratio (4) was the best in terms of larval development during the zoeal stages and resulted in improved metamorphosis. Dietary ARA seemed to improve first metamorphosis, but its exact role needs further clarification. For the larval rearing of S. paramamosain, an enrichment medium containing about 30% total n-3 HUFA with a minimum DHA/EPA ratio of 1 is recommended. Further investigation is needed on the total HUFA and optimum DHA/EPA ratio requirements for each crab larval stage.

Few marine rotifer species (e.g. Encentrum linheii and Synchaeta cecilia) have been cultured successfully besides Brachionus plicatilis and B. rotundiformis, commonly used to rear larvae of many marine fish species. The development of culture techniques for marine rotifers smaller in size than the Brachionus species may be useful for rearing fish species for which the currently used prey are too large. We evaluated the possibility of culturing Colurella dicentra isolated from a Mississippi Gulf Coast estuary. An experiment was conducted to determine the effects of salinity (10–35 g L−1) on its population growth rate. Rotifers were fed Nannochloropsis oculata at a density of 100 000 cells mL−1 for 15 days. Colurella dicentra survived in water with a salinity of 10–47 g L−1. Densities of up to 300 rotifers mL−1 were sometimes attained in cultures. Salinity influenced C. dicentra production (P 0.05), but were higher (P=0.05) than numbers at 25 g L−1 (4240±1783), 30 g L−1 (1300±264 SD) and 35 g L−1 (100±101 SD). The population growth rate (r) of the rotifers was the highest at 15 g L−1 (0.37–0.42 day−1), and the lowest at 35 g L−1 (−0.33–0.06 day−1). This is the first report of C. dicentra in the estuarine waters of the Gulf of Mexico, and also the first time it has been cultured successfully.

The effects of light intensity on feeding incidence and prey consumption at first feeding of spotted sand bass larvae (Paralabrax maculatofasciatus Steindachner), using four light intensity treatments (0, 100, 400, and 700 lx) were evaluated. Specimens were fed the rotifer Brachionus plicatilis at a density of 3 rotifers mL−1. One hour after the addition of prey, 30±3 (mean±SEM) larvae were sampled from each treatment aquarium. Feeding incidence was evaluated as the percentage of larvae with prey in the digestive tract. Feeding intensity was measured as the number of prey in the digestive tract of the larvae. Histological analysis was carried out to describe the eye structure at the time of first feeding. Larvae fed in darkness (0 lx) had a significantly lower (P 0.05) between light treatments. Histological analysis of the eye structure showed that first feeding larvae had well-formed lens along with a retina composed of pure single cones as photoreceptors.

Two feeding experiments were conducted to determine if Brachionus plicatilis and Artemia salina nauplii were ingested by mud crab Scylla serrata larvae. In the first experiment, larvae were fed with increasing densities of Artemia nauplii with or without Brachionus to determine consumption with increasing densities of Artemia and with increasing zoeal stage. This experiment also aimed to determine if the presence of Brachionus as an alternative prey influenced the intake of Artemia by the crab larvae. There was generally an increase in intake with increasing densities of Artemia and increased consumption of Artemia as the larvae grew. Consumption of Brachionus was consistently high in all zoeal stages. There was a significant reduction in the intake of Brachionus with increasing consumption of Artemia in the early zoeal stages (Z1, Z2, Z3), but at later stages (Z4, Z5) the intake of Artemia was no longer affected by the presence of Brachionus. In the second experiment, daily ingestion within instar of zoeal stages and megalopa were compared. There was an increased consumption of Artemia nauplii on the day before molting and increased ingestion of Brachionus on the day after larvae had molted, except at Z3. Megalopae exhibited a decline in Artemia nauplii intake on the days before metamorphosis to crablet.

Sunshine bass, a hybrid of female white bass Morone chrysops (Rafinesque) and male striped bass M. saxatilis (Walbaum), fingerling production occurs almost exclusively in ponds. To increase production and maintain year-round production in temperate climates, indoor tank culture is required. While tank production of fingerlings has been demonstrated, little is known about feeding requirements. Sunshine bass larvae, stocked at 75 L−1 in 100 L of brackish water, were fed sequentially with rotifers Brachionus plicatilis cultured with a Nannochloropis algae paste and enriched with highly unsaturated fatty acids, decapsulated Artemia nauplii, and a microencapsulated commercial diet. The larvae in one treatment (three replicates) were initially fed rotifers at a daily rate of 20 mL−1, then nauplii at an initial rate of 2 mL−1, and then the commercial diet at 1 g. Larvae in two other treatments received two and three times as much food daily. The highest feeding rate resulted in a survival (52.9%) that was significantly higher than the survival rate (22.4%) of larvae fed the least. The total biomass produced was the highest in the treatment receiving the most food. The lowest feeding rate produced the least fish, but they were the heaviest. The intermediate feeding rate produced the shortest fish (11.3 mm).

The rotifer Brachionus plicatilis was fed in experimental conditions with a small celled (2–5 μm) Chlorella sp. and a large celled (16–22 μm) Asteromonas gracilis algae. The specific growth rate (SGR) of rotifers fed Asteromonas (maximum 0.79) was statistically higher than that for rotifers fed Chlorella (maximium 0.61). The filtration and ingestion rates using different rotifer and algal densities exhibited certain maxima depending on the species, the cell density and the condition of the rotifers. The filtration rate was higher with Asteromonas and, although ingestion rate was lower than with Chlorella, the ingestion in terms of cell volume was 10-fold higher. It seems that B. plicatilis ingests the larger cell diameter algal species more efficiently than the smaller species that is usually used for its mass culture.

The ability for food selectivity of rotifer Brachionus plicatiliswas studied in the laboratory by feeding mixtures of microalgae with various cell volumes. Chlorella sp. (≈22 µm3) was the reference algal species, and Asteromonas gracilis, (Chlorophyta) (≈2150 µm3), Tetraselmis suesica (≈268 µm3), Dunaliella salina (≈52 µm3) and Chaetoceros sp. (≈150 µm3) the experimental species. Each was mixed with Chlorella and fed in three experiments. In the first experiment, filtration and ingestion rates of rotifers each fed with algae revealed that the highest values were measured with the mixture of Chlorella + Asteromonas, and the lowest for Chlorella + Chaetoceros. In the second and the third experiments, by using several combinations of algal densities with the mixture of Chlorella + Asteromonas, a selectivity ability of the rotifers for Asteromonas was found. A hypothesis is presented that accounts for the preference of rotifers for Asteromonas, which is suggested as a new candidate species for use in live food production of fish hatcheries.

Studies were carried out to determine the effect of using the rotifer, Brachionus plicatilis (Muller) (S-type), subjected to different treatments on the growth and survival of blue-fin sea bream, Sparidentex hasta (Valenciennes), larvae. This was to illustrate the role of mixed algae added to the oil enrichments for the treatment of the rotifers to improve the sea bream larval survival. The highest sea bream larval survival (P 0.05) in the larval growth was observed between different treatments. However, larval survival was significantly high (P

Gamma-aminobutyric acid (GABA) has been shown to enhance the reproduction of the rotifer Brachionus plicatilis Muller in stressful culture conditions. During the enrichment of rotifers for feeding to marine fish larvae, they are usually stressed as a result of exposure to different marine oils and high population densities. This typically results in decreased rotifer survival, reproduction and swimming activity. In the present study, we used GABA to increase rotifer reproduction and the swimming activity of rotifers in enrichment cultures. GABA treatment 24 h before high density enrichment enhanced reproduction during enrichment culture, but not when carried out simultaneously with enrichment. Swimming activity was not significantly affected by GABA treatment 24 h before or simultaneously with nutrient enrichment.

Mass production of rotifers is essential as live food during the larval rearing season, but a major problem of rotifer culture is unpredictable culture collapse. If mass-produced rotifers could be kept alive at low temperature for an extended period of time, they could be supplied as live food to cultured marine fish larvae without interruption. Four experiments were performed to test this possibility in six strains of Brachionus plicatilis O. F. Muller and eight strains of Brachionus rotundiformis Tschugunoff. The results showed that: (1) B. rotundiformis strains were less tolerant to 4 ∞C than B. plicatilis strains. Among the B. rotundiformis strains, the strains known as SS type were the most susceptible and showed the lowest survival. (2) Exchange of culture media during the incubation at 4 ∞ Ci nB. plicatilis and B. rotundiformis resulted in higher survival than not changing the culture media, but there were no differences in the regression slope with or without changing the culture media. (3) Acclimation at 15 ∞C for 96 h for B. plicatilis and B. rotundiformis before transfer to 4 ∞C resulted in higher survival rates than acclim- ation at 10 ∞C. (4) The combination of frequent exchange of culture media and acclimation sig- nificantly improved the survival of B. plicatilis and B. rotundiformis compared with controls that were maintained at 4 ∞C without exchange of the culture media. Large-scale trials using B. plicatilis (Kamiura strain) cultured in 30-L tanks were conducted in a hatchery at a density of 2000-20 000 individuals mL -1 . Rotifers were transferred directly from 25 ∞C to 4 ∞C. About 50% of the rotifers at 20 000 individuals mL -1 survived after 14 days at 4 ∞C. These preserved rotifers could be cultured at 20 ∞C, recovering within 4 days.

Despite the fact that the suitability of copepods as live prey for marine fish larvae is now well established, their use in aquaculture remains sporadic. Although of lower nutritional value, the relative ease of production of rotifers (Brachionus spp.) and Artemia nauplii continues to ensure their predominance. Studies in the literature have highlighted differences in the levels and ratios of fatty acids, lipid classes and pigments between copepods and traditional live prey. Such differences may have important consequences for fish larval nutrition. The consequences of poor nutrition during fish larval development may be obvious, for example deformities or malpigmentation, but in many cases may be obscure, as in affects on temperature tolerance or growth during later life stages. In some aquaculture systems, copepods are cultured in large quantities in outdoor, extensive or semi-intensive units. Intensive-rearing systems for copepods require further development. However, it is now established that intensive rearing on monoalgal diets does not result in severe deterioration of the nutritional value of the copepods, at least in terms of their highly unsaturated fatty acid (HUFA) content. In some cases, the provision of copepods for a short period of time during the larval stage is sufficient to ensure normal development. However, it remains to be demonstrated that the extra costs involved result in increased profits as a result of higher percentages of normally pigmented juvenile fish, improved growth and survival and reduced incidence of disease. This paper reviews the advances in production systems for copepods, their nutritional value as live prey for fish and their present and potential use in aquaculture.

Based on the results of individual and batch culture experiments in small volumes, we conducted experiments in larger volumes of 100 mL, 1 L and 10 L to determine: (1) at what phase of population growth would gamma-aminobutyric acid (GABA) treatment be most effective; and (2) whether GABA treatment of concentrated rotifers for several hours before mass culture would also be effective. GABA treatment of rotifer cultures at lag phase significantly enhanced population growth, whereas treatment at log phase had a lesser effect, and treatment at stationary phase had no effect. Addition of GABA to rotifer cultures every 2 days hastened population growth until day 8, but resulted in culture collapse thereafter. To reduce the cost of the use of GABA in mass cultures, GABA treatment may be conducted on concentrated rotifers (100 individuals mL−1) before mass culture. GABA treatment of concentrated rotifers for 24 h and 48 h before mass culture resulted in a significantly higher population density compared with their respective controls (no GABA treatment) on day 4, and on days 4 and 6 respectively.

A commercial microencapsulated diet was used as a total or partial replacement of live prey for feeding larvae of winter flounder Pseudopleuronectes americanus (Walbaum), a potential alternative finfish species for coldwater marine aquaculture. Growth performance (morphometric measurements and biochemical composition) and nutritional condition (RNA/DNA ratios) of larvae fed live prey (Brachionus plicatilis Muller), a microencapsulated diet or a mixed diet of live prey and microcapsules were compared. Newly hatched larvae were unable to digest microencapsulated diet; live prey at initial feeding was required for their survival and growth. Larvae offered a mixed diet showed slower growth than larvae fed exclusively with live prey. However, at the onset of stomach differentiation, RNA/DNA ratios (indicators of protein synthesis potential) of the larvae fed both diets became similar. We suggest that, at that stage (size 5.5–6.3 mm), enzymatic activity had developed enough to allow digestion of inert food. As the RNA/DNA ratio is a good indicator of nutritional condition, it appears to be an interesting tool for the assessment of diet adequacy in marine larval feeding technology.

Substrates that are cleaved to yield fluorescent products can be used to quickly quantify enzyme activity in vivo with image analysis or in vitro with fluorometry. This study was carried out to determine whether enzyme activity in rotifers is useful for assessing the physiological condition of rotifers. Neonates of Brachionus plicatilis Muller hatched from cysts were exposed to a concentration series of unionized ammonia ranging from 0 to 9.8 p.p.m., increasing seawater viscosity relative to 1.17 to control sea water by the addition of methyl cellulose and the addition of the protozoan Euplotes sp. to a density of 40 mL−1. Rotifer glucosidase and esterase activities decreased with increasing unionized ammonia and viscosity respectively. Activities of glucosidase and phospholipase decreased with increasing protozoan contamination. There was a significant relationship between enzyme activities and rotifer population growth. In vivo activities of certain rotifer enzymes can therefore serve as biomarkers for the rapid assessment of environmental stressors in rotifer mass cultures.

The gilthead seabream Sparus aurata L. is a sequential spawner whose reproductive cycle can be manipulated to obtain year-round egg and fry production. Hence, there is an overproduction of eggs in commercial hatcheries that is normally wasted. Two feeding experiments were conducted with the purpose of investigating the potential use of fresh and freeze-dried gilthead seabream eggs for the enrichment of live preys. The first experiment was also designed to study the possibility of using freeze-drying as a conservation process for eggs in excess. Larvae were reared for 20 days after hatching (DAH),on a diet of Brachionus sp. As experimental controls, the commercial enrichment emulsion SUPER HUFA was used in the first experiment, and the microalgae Nannochloropsis sp. in the second. This study demonstrated the potential of gilthead seabream eggs as an enrichment product to be used in the feeding of the first larval stages of Sparus aurata L. The data obtained emphasize the need to have an overall perspective of the nutritional requirements of the organisms in culture.

The effect of a potential probiotic on the growth performance of a rotifer and its inhibition against Vibrio anguillarum was studied. Probiotic strain AR21 had no significant observable effect on the growth rate of rotifers under optimal culture conditions in three consecutive experiments. In the first and second experiments, the AR21 strain exhibited an inhibitory effect against the V. anguillarum strain when rotifer cultures were maintained at a suboptimal feeding regime. The growth rate of the rotifers in suboptimal feeding conditions was significantly higher in the treatment receiving AR21 and V. anguillarum than in the treatment where only V. anguillarum was added.

Scanning electron microscopy indicated that stored resting eggs of the marine rotifer Brachionus plicatilis Muller were colonized by numerous bacterial cells that affect the hatchability of resting eggs. The effectiveness of chemical disinfectants on the hatching of the resting eggs was studied using selected chemicals and antibacterial drags. The hatching success rate of the fresh and stored eggs was 26 ± 5.8% and 0%, respectively. Sodium hypochlorite (1.0 p.p.m.) increased the hatching rate to 48 ± 1.3% in freshly-collected and 28 ± 1.8% in stored eggs. Physical disintegration of the bacterial mat occurred after 1 h of treatment with sodium hypochlorite. Among antibacterial drugs, sodium nifurstyrenate (Erubaju) enhanced the hatching success rate to 40 ± 1.2% and 20 ± 1.1% for the freshly-collected eggs and stored resting eggs, respectively. However, tetracycline and oxytetracycline did not significantly influence the hatching of the stored eggs. These observations are discussed in relation to the development of an improved method for the processing and hatching of rotifer resting eggs.

Essential oils extracted from three plant species of the genus Origanum, Origanum vulgare subsp. hirtum, Origanum onites L. and Origanum marjorana L., were assayed as potential antibacterial agents for disinfection of rotifers Brachionus plicatilis. Survival of rotifers in seawater with added oregano essential oils was significantly higher than in the control treatment (P 0.05), while the numbers of presumptive Vibrio in rotifers were significantly reduced compared with the control treatment (P