Developing the harpacticoid copepod Tisbe biminiensis culture: testing for salinity tolerance, ration levels, presence of sediment and density dependent analyses

Copepods have a number of advantages for use as live food in cultures of fish and crustacean larvae. This study aimed to develop culture techniques of Tisbe biminiensis Volkmann‐Rocco 1973 in volumes of 500 mL. The first experiment tested the effect of salinity on survival and fecundity. The other experiments studied the population growth comparing two levels of daily ration and the effect of sand sediment in cultures. The cultures were carried out on plastic boxes at 29°C, salinity of 34 g L^?1 and 12 h light/12 h dark photoperiod with aerated filtered seawater, total renewal every other day. Adult females tolerated the decrease of salinity from 34 to 27 g L^?1 but the offspring production decreased significantly. The salinity of 20 g L^?1 was not tolerated at all. Tisbe biminiensis attained one of the highest rates of increase in cultures among harpacticoids (0.33 day^?1) and a high density of 205 individual ind. mL^?1. The carrying capacity of the population was estimated as 67 200 ind. in 500 mL recipients. In conclusion, T. biminiensis grow fast and attain high densities in cultures of 500 mL volume without sediment, feeding a daily ration of 50–100% of copepodite biomass.     

Interactions between populations of the calanoid copepod Acartia tonsa Dana and the harpacticoid copepod Tisbe holothuriae Humes in mixed cultures of live feed for fish larvae

Copepods are considered high quality live feed for fish larvae due to their large within species size span, swimming pattern triggering hunting behaviour, and complete biochemical profile. In a continuous cultivation system aiming at the planktonic calanoid Acartia tonsa an intruding harpacticoid frequently appears. We experimentally evaluate how the interaction from the semi‐benthic Tisbe holothuriae is affecting our cultures and ask whether the two copepod‐species are expected to pose competitive exclusion or co‐exist long‐term. This is pursued by establishing ~40 days mono‐ and mixed copepod cultures reared in a stationary setup (S) theoretically advantageous for T. holothuriae and a rotating setup (R) with organisms kept in suspension by use of a plankton wheel, theoretically advantageous for A. tonsa. The carrying capacities of A. tonsa in either mono‐ or mixed cultures are not affected whether the copepods are subject to S or R treatment. Only exception is the S‐setup containing mixed culture were A. tonsa obtains a significantly lower carrying capacity compared with A. tonsa alone in R‐setup. The mono‐ and mixed cultures of T. holothuriae are, however, highly negatively affected by the R setup compared with S setup. A long‐term solution to limit the presence of T. holothuriae is to apply turbulence level in a classical stagnant tank setup to an extend that suppress T. holothuriae and simultaneously allow algae in suspension as food for A. tonsa, make their eggs sediment as well as minimize risk of benthic‐predation on eggs.     

Essential fatty acid enrichment of cultured rotifers (Brachionus plicatilis, Müller) using frozen-concentrated microalgae

There is a growing interest in preserving microalgal preparations to maintain constant properties over a long period. The aim is to ensure sufficient delivery of essential fatty acids (and other key nutrients) to mollusc and crustacean larvae and to zooplankton used as live prey in the first feeding of fish larvae. For example, the rotifer Brachionus plicatilis has to be enriched with polyunsaturated fatty acids (PUFA) prior to fish feeding. We used four microalgal species [ Isochrysis galbana (T-ISO), Chaetoceros muelleri (CHGRA), Pavlova lutheri (MONO), and Nannochloropsis sp.] both as fresh culture or in a frozen-concentrated form to enrich rotifers. Overall, rotifers had similar relative fatty acid levels when fed the frozen-concentrated or fresh microalgal diets. The levels of 20:4n-6, 22:6n-3, and 20:5n-3 between B. plicatilis and the microalgal diets were linearly correlated. The fatty acid 20:4n-6 was the most readily assimilated: the content found in rotifers reached half the level measured in the microalgal diets. Our results indicate that both the fresh and frozen-concentrated forms of the four microalgal species can be used to enrich PUFA levels in rotifers. Further experiments should be conducted to test if assimilation differs when rotifers are enriched with mono- or multispecific microalgal preparations.     

Examination of a practical method for copper enrichment of euryhaline rotifers (Brachionus plicatilis) as diet of Eriocheir sinensis zoea larvae

In this study, an effective method to enrich the rotifer Brachionus plicatilis with copper was developed as a feed for the Chinese mitten crab Eriocheir sinensis zoea larvae. Changes in the concentrations of other minerals in rotifers were also examined when copper was added for rotifer enrichment. The ability of Chlorella to absorb waterborne copper is much higher than that of rotifers, and hence, copper was preaccumulated in Chlorella before its ingestion by rotifers. The copper content in rotifers was comparable to the dietary copper requirement of the crab larvae when the rotifers were enriched with 0.1 mg Cu g⁻¹ Chlorella for 12 h. Further enrichment in rotifers with Cu‐enriched Chlorella and lipid emulsions did not significantly change the profile of major fatty acids and mineral composition in the rotifers. Evidence shows the feasibility of copper enrichment in rotifers using microalgae that can accumulate copper. This study indicates that copper in rotifers can be enriched by feeding copper‐enriched algae at a concentration of 0.1–0.2 mg Cu g⁻¹ Chlorella. The developmental rates of E. sinensis can be improved by feeding zoea larvae with copper‐enriched rotifers, but survival rates were not affected by dietary copper enrichment.     

Evaluating bioencapsulation of florfenicol in rotifers (Brachionus plicatilis)

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.     

Biochemical and technical observations supporting the use of copepods as live feed organisms in marine larviculture

The use of live prey is still necessary for a large number of raised fish species. Small sized rotifers are usually used as live preys during the first days of feeding in small mouth fish. An alternative to this is the use of copepods as prey for first feeding. In this study, the sizes, weight and biochemical contents of two copepods and one rotifer species raised on similar algal food conditions were compared. Rotifers contained a higher proportion of essential amino acids in the free amino acid (FAA) fraction (43%) than copepods (30–32%). However, rotifers had lower levels of important fatty acids like DHA (7% compared with 23–32% in copepods) and their DHA/EPA ratio was lower than that in copepods (0.54 compared with 1.35–1.63 in copepods). The FAA pattern of the preys tended to be species‐specific and its implications from an aquaculture point of view is discussed. In contrast, the‐protein bound amino acids tended to be very conservative among the studied organisms. The second part of the work is focused on ‘the price’ of hatching in Acartia tonsa eggs before or after cold storage at 3°C. The fatty acid contents in A. tonsa tended to decrease with the storage time. It also decreased with hatching of the nauplii, but its proportion compared with the dry weight remained constant.     

Use of essential oils extracted from three Origanum species for disinfection of cultured rotifers (Brachionus plicatilis)

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). When rotifers were incubated in seawater with added oregano essential oils at a final concentration of 10 mg L^?1 for 4 h, the numbers of total culturable bacteria were not significantly lower 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 < 0.05).     

Natural zooplankton as larval feed in intensive rearing systems for juvenile production of Atlantic cod (Gadus morhua L.)

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.     

Effects of adult stocking density on egg production and viability in cultures of the calanoid copepod Acartia tonsa (Dana)

The effect of stocking density of the calanoid copepod Acartia tonsa was evaluated in a 96 h rearing experiment. Possible density‐dependent egg production and egg viability were analysed at stocking densities of 100, 200, 300, 400 and 600 adults L⁻¹. Temperature, oxygen saturation and algal concentration were kept optimal. A non‐density‐dependent mortality rate of 15–19% day⁻¹ was documented. A non‐significant density‐dependent egg production was observed between 100 and 600 adults L⁻¹. The average egg production was 22.5±8.8 egg female⁻¹ day⁻¹ in all densities. The average egg hatching success was 84.7±4.8% and was never observed below 76.1%, with no significant differences across the stocking densities. Conclusively, as a practical recommendation for the aquaculture industry, copepod cultures with densities ranging from 100 to 600 adults L⁻¹ and presumably even more dense cultures are possible with the studied species obtaining a steady egg production and still high egg viability.     

The effect of different HUFA enrichment emulsions on the nutritional value of rotifers (Brachionus plicatilis) fed to larval haddock (Melanogrammus aeglefinus).

A feeding study was conducted in the winter 2001 to determine the effects of feeding rotifers (Brachionus plicatilis) enriched with various levels of essential fatty acids on the growth and survival of haddock larvae (Melanogrammus aeglefinus). Rotifer enrichment treatments were: 1) mixed algae, 2) high DHA (docosahexaenoic acid, 22:6n-3), 3) high DHA and EPA (eicosapentaenoic acid, 20:5n-3), and 4) DHA, EPA, and AA (arachidonic acid, 20:4n-6). Larvae were fed rotifers enriched with the different treatments from days 1 to 16 post-hatch. From day 17 until 25 all treatment groups were fed rotifers reared on mixed algae and then weaned onto the International Council for Exploration of the SEA (ICES) Standard Reference Weaning diet (http://allserv.rug.ac.t/aquaculture/rend/rend.htm) over a five day period. The experiment was terminated on day 41 post-hatch. The enrichment treatments affected the fatty acid composition of the rotifers and correlated with the accumulation of these fatty acids in the haddock larvae. However, no significant differences in larval growth or survival to 40 days post hatch were detected, suggesting that all treatments provided the minimal essential fatty acid requirements for haddock.     

Biochemical composition and fatty acid profile in a strain of the lineage ‘Nevada’, belonging to the Brachionus plicatilis (Rotifera) complex,fed different diets

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.     

Effect of the addition of diatoms (Navicula spp.) and rotifers (Brachionus plicatilis) on water quality and growth of the Litopenaeus vannamei postlarvae reared in a biofloc system

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.     

Effects of selenium supplementation on the antioxidation response in the rotifer (Brachionus plicatilis)

In the present study, the effects of selenium (Se) enrichment on the rotifer, Brachionus plicatilis, were investigated. Based on the results of six Se treatments obtained from triplicate experiments, we found that the efficiency of bioaccumulation by Se from non‐acid‐soluble sources was 62‐fold greater than that from acid‐soluble sources (Se‐Chlorella 15.6 ± 1.81% vs. selenite 0.25 ± 0.03%). However, supplementation of both acid‐soluble Se at low concentrations (≤40 µg per thousand rotifers) and Se‐Chlorella enhanced rotifer lifespan, increased the rate of spawning, inhibited lipid peroxidation, decreased levels of intracellular oxidization products and maintained the stability of mitochondrial membranes. These positive effects were correlated with the activities of antioxidant enzymes (e.g. catalase‐ and guaiacol‐dependent peroxidase) which increased along with the low Se concentrations (<80 µg per thousand rotifers). In contrast, the opposite effects were found when the rotifers were exposed to high Se concentrations (≥80 µg per thousand rotifers). The antioxidation and toxicity effects appeared to be correlated with the levels of total Se bioaccumulation. Above all, selenite, which is more toxic than Se‐chlorella, is less readily accumulated and biologically active. Se‐enriched rotifers fed by Se‐Chlorella are a fish larvae food supplement in aquaculture.     

The enrichment of rotifers (Brachionus plicatilis) and Artemia franciscana with taurine liposomes and their subsequent effects on the larval development of California yellowtail (Seriola lalandi)

Taurine is an essential or conditionally essential nutrient for many species of marine fish, especially during early development. There is growing evidence that marine fish larvae benefit from taurine‐enriched rotifers; however, it is unknown if larvae benefit from taurine‐enriched Artemia. We investigated the effects of taurine‐enriched rotifers (Brachionus plicatilis) and Artemia franciscana on the growth and whole‐body taurine concentrations of California yellowtail (Seriola lalandi; CYT) larvae. The approach used in this study was to encapsulate taurine within microparticles (liposomes), which were then fed to rotifers and Artemia. We found that feeding taurine liposomes to rotifers and Artemia resulted in taurine concentrations in these prey species that were similar to or above those previously reported in copepods. At the end of the rotifer phase, CYT larvae fed taurine‐enriched rotifers showed increased growth (final dry weights; DW) and had higher whole body taurine concentrations when compared to larvae fed unenriched rotifers. At the end of the Artemia phase, CYT whole body taurine concentrations varied among dietary treatments. Larval lengths and DWs were not significantly different among treatments at the end of the Artemia phase, suggesting that the taurine concentrations of unenriched Artemia were sufficient to support the growth of CYT larvae.     

Use of a potential probiotic Lactococcus lactis AR21 strain for the enhancement of growth in the rotifer Brachionus plicatilis (Müller)

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.     

Morphometric changes in a strain of the lineage 'Nevada', belonging to the Brachionus plicatilis (Rotifera) complex

The rotifer Brachionus plicatilis is an important component of aquaculture as a larval feed. Its taxonomic status has been recently re-defined as a species complex, consisting of at least 14 new species/lineages. This study deals with the lineage Brachionus 'Nevada', which has been shown to occur in European hatcheries. A strain of B . 'Nevada' was mass cultured using two commonly applied feeding regimes and analysed in terms of its morphometry. A new formula was proposed for the calculation of volume, which can be used as an index of adequacy of rotifers as feed for fish larvae. The results were related to life cycle parameters. The pre-reproductive and reproductive phases were divided into distinct size groups. Differences were also found between the two diets in morphometry and demography. Rotifers of a larger size (yeast-based diet) showed a lower growth rate and a longer reproductive period, lifespan and mean generation time compared with smaller-sized rotifers (Culture Selco^®-based diet). In terms of lorica length, the present study's strain of B . 'Nevada' (238.5 μm) was intermediate between values reported for Brachionus ibericus (193.5 μm) and B. plicatilis sensu stricto (299 μm).     

Relationship between daily survival rates of larval Japanese anchovy (Engraulis japonicus) and concentrations of copepod nauplii in the Seto Inland Sea, Japan

We attempted to estimate the survival rates of larval cohorts (3–15 mm in body length) of the Japanese anchovy Engraulis japonicus population in Hiuchi‐nada, Seto Inland Sea, Japan, and examined the relationship to their food availability. The survival rates were directly calculated from the change in larval density during the survey. The estimated daily survival rate ranged between 0 and 89% d⁻¹, but increased with the increase in the mean concentration of small‐sized copepod nauplii (<100 μm in body length) sampled at 10 m depth. When the food concentration was higher than about 5 nauplii L⁻¹, the daily survival rate of larval anchovy reached an asymptote of approximately 89% day⁻¹. It might be possible to provide a framework for the forecast for larval abundance immediately prior to recruitment size (10–15 mm SL), based on larval abundance of the monitored size (3–8 mm SL) and the survival rate which is estimated from the concentration of small‐sized nauplii.     

Testing the yield of a pilot‐scale bubble column photobioreactor for cultivation of the microalga Rhodomonas salina as feed for intensive calanoid copepod cultures

A dual column photobioreactor (PBR) (2 × 47 L) with mixed CO₂/air bubbling was tested for cultivation of the microalga Rhodomonas salina as food for live feed copepods. In the continuous growth phase, the cell density was relatively stable at 2.40 ± 0.13 × 10⁶ cells/ml at an average dilution rate of 0.46 ± 0.02 per day throughout the 30‐day experiment. The produced algae had a high content of both total fatty acids (TFA) and free amino acids (FAA). Especially, the harvested algae contained a high proportion of poly‐unsaturated fatty acids that made up 80% of the TFA and of essential amino acids (35% of all FAA), implicating desirable components as feed for copepods. The current PBR was sufficient to feed a culture of the calanoid copepod Acartia tonsa at a density of 2,500 adult/L in ca. 500 L culture with a daily yield of approximately 17 × 10⁶ eggs. To be able to sustain the integrated copepods production, the suggested volume of the algae cultures should be ca. 20% of the copepod culture volume.     

Cyprinid herpesvirus 3 as a potential biological control agent for carp (Cyprinus carpio) in Australia: susceptibility of non‐target species

Carp (Cyprinus carpio L.) is a pest species in Australian waterways, and cyprinid herpesvirus 3 (CyHV‐3) is being considered as a potential biological control (biocontrol) agent. An important consideration for any such agent is its target specificity. In this study, the susceptibility to CyHV‐3 of a range of non‐target species (NTS) was tested. The NTS were as follows: 13 native Australian, and one introduced, fish species; a lamprey species; a crustacean; two native amphibian species (tadpole and mature stages); two native reptilian species; chickens; and laboratory mice. Animals were exposed to 100–1000 times the approximate minimum amount of CyHV‐3 required to cause disease in carp by intraperitoneal and/or bath challenge, and then examined clinically each day over the course of 28 days post‐challenge. There were no clinical signs, mortalities or histological evidence consistent with a viral infection in a wide taxonomic range of NTS. Furthermore, there was no molecular evidence of infection with CyHV‐3, and, in particular, all RT‐PCRs for viral mRNA were negative. As a consequence, the results encourage further investigation of CyHV‐3 as a potential biocontrol agent that is specific for carp.