Effect of cultivation methods on nutritional enrichment of euryhaline rotifer <Emphasis Type="Italic">Brachionus plicatilis</Emphasis>

This study aimed at comparing fatty acid contents of rotifers cultured with different methods after nutritional enrichment in order to evaluate the rotifer quality produced by these methods. Rotifers were cultured using either a batch or a continuous culture. From the batch culture, three experimental subpopulations were used, sampled from the culture at 1, 24, and 48 h after rotifer inoculation. The continuous culture was performed with two tanks; one was for cultivation with continuous feeding and water supply (cultivation tank), and another was for harvesting from the cultivation tank by overflow (harvest tank). From the continuous culture, two subpopulations were used: one from the cultivation and one from the harvest tank. Nutritional enrichment was performed after each culture. Each population was enriched with Nannochloropsis oculata or a commercial enrichment diet. When the enrichment was performed with N. oculata on populations at 24 h after inoculation originating from either of the two tanks of continuous culture or the batch culture tank, a higher quantity of arachidonic acid (ARA) and eicosapentaenoic acid (EPA) was obtained from the two tanks of continuous culture. The same results were obtained when enrichment diet was used, this time including docosahexaenoic acid (DHA).     

几种单胞藻对褶皱臂尾轮虫的营养强化研究

利用气相色谱法测定了小球藻、牟氏角毛藻、球等鞭金藻和投喂不同藻类后12h的褶皱臂尾轮虫的脂肪酸含量。试验结果表明,不论是投喂单种藻类还是2种混合藻类,强化后的轮虫其体内的脂肪酸含量均发生了明显变化,其中单链脂肪酸及低度不饱和脂肪酸的含量在投喂前后没有变化,各种脂肪酸的含量界于未强化的轮虫和所投喂的单胞藻饵料含量之间。3种高度不饱和脂肪酸的含量,除了二十二碳六烯酸因在牟氏角毛藻中含量较低,在单独投喂牟氏角毛藻后的轮虫中未检测出外,其余均与其所投喂的单胞藻的脂肪酸一致;轮虫中被检出的3种高度不饱和脂肪酸的含量,在单种藻类试验组中均低于所投喂藻类的含量;在2种藻类混合试验组中界于2种单胞藻含量之间。混合藻类比单种藻类强化轮虫具有更加全面的营养效果。     

Enriching rotifers with “premium” microalgae. Isochrysis aff. galbana clone T-ISO

The effect of semi-continuous culture on the nutritional value of microalgae was tested in the rotifer Brachionus plicatilis in short-term enrichment experiments. Isochrysis aff. galbana clone T-ISO was cultured semi-continuously with renewal rates from 10 to 50% of the volume of the culture per day and used to feed the rotifers. After 24 h, dramatic differences in dry weight and protein, lipid and carbohydrate contents were observed in the rotifers depending on the renewal rate applied to the microalgal culture. Rotifers fed T-ISO cultured with low renewal rates showed low dry weight and organic content, whereas rotifers fed microalgae from nutrient-sufficient, high renewal rate cultures showed higher dry weight and increases up to 60% in protein, 35% in lipid and 100% in carbohydrate contents. Feed conversion rate (FCR) and organic FCR decreased with increasing renewal rates, indicating a more efficient assimilation of the microalgal biomass obtained at high growth rates. The fatty acid profile of rotifers reflected that of T-ISO, with maximum content of polyunsaturated fatty acids (PUFAs), n-3 fatty acids and docosahexaenoic acid (DHA) being found in the rotifers fed microalgae from the renewal rate of 40%. Results demonstrate that the biochemical composition of B. plicatilis is strongly modified through the use of semi-continuous cultures of microalgae in short-term enrichment processes. This technique provides an excellent tool to improve the nutritional value of the live feed used in fish larvae cultures.     

Improvement of larval rearing technique for mass seed production of snow crab <Emphasis Type="Italic">Chionoecetes opilio</Emphasis>

Larval rearing experiments were conducted to examine the potential for mass seed production of the snow crab Chionoecetes opilio using a total of eight 20-kL tanks. Tanks were equipped with agitators, which move the water using a rectangular blade to prevent the zoeas sinking to the bottom of the tank. Larval rearing water was treated with sodium nifurstyrenate once a week to reduce the chance of larval infection by pathogenic bacteria. Zo eas were fed with rotifers and Artemia nauplii. A total of 122 830 megalops and 16 660 first-stage crabs were produced. Thus, the potential for mass seed production of snow crab was determined. Survival rates up to the megalopal stage were high in tanks with a feeding regime that fed rotifers to larvae through an entire zoeal stage. This study also describes the fatty acid composition of snow crab larvae. It revealed that the first zoeas had a high DHA content and DHA/EPA ratio, but these values significantly decreased in the second stage zoeas and megalops. Improving the DHA content and/or DHA/EPA ratio of larvae should be important in studies on mass seed production technology of the snow crab.     

Effect of enriched live feeds on survival and growth rates in larval Korean rockfish, Sebastes schlegeli Hilgendorf

High mortality frequently occurs in larval mass production of Korean rockfish, Sebastes schlegeli Hilgendorf. Nutritional deficiencies in live feeds, rotifers and Artemia nauplii, fed to larvae could be a reason. A series of experiments was carried out to evaluate the effect of nutritional enrichment of live feeds by ω‐yeast, Spirulina powder and Super Selco^TM on survival and growth rates in rockfish larvae. Preference of rockfish larvae for the live feeds was determined by analysis of stomach contents. In addition, the effect of green water produced by the use of Chlorella ellipsoidea and Spirulina powder on the growth performance of larvae was evaluated. Larvae fed rotifers nutritionally enriched with Super Selco showed significantly higher survival rates than those fed rotifers enriched with ω‐yeast. Larvae fed rotifers that were nutritionally enriched with both Super Selco and Spirulina together exhibited improved growth and survival rates. Larvae fed Artemia nauplii nutritionally enriched with Spirulina powder showed significantly higher survival than larvae fed Artemia nauplii without enrichment. When larvae were fed rotifers, Artemia nauplii or the mixture of rotifers and Artemia nauplii, the second and last group showed significantly higher survival than the first group. Fatty acid composition in live feeds was improved by enrichment of ω‐yeast and larvae fed this feed showed higher survival and growth rates compared with larvae fed non‐enriched feeds. No positive effect of green water in the tank produced with C. ellipsoidea or Spirulina powder was observed on survival and growth rates for larvae fed nutritionally enriched rotifers with Super Selco and Spirulina powder. However, when the larvae were fed Artemia nauplii that were nutritionally enriched with ω‐yeast and Spirulina powder, green water obtained by adding Spirulina powder to the tanks resulted in significantly higher growth rates of larvae than was obtained by adding C. ellipsoidea.     

Iodine‐enriched rotifers and Artemia prevent goitre in Senegalese sole (Solea senegalensis) larvae reared in a recirculation system

To study the effect of dietary supplementation of iodine in Solea senegalensis, larvae were randomly distributed in six tanks. Larvae in three tanks were given rotifers and Artemia enriched with iodine in addition to Rich Advance or Super Selco from 2 days after hatch (DAH) until 31 DAH. Larvae in a second set of three tanks were fed control rotifers and Artemia, enriched only with Rich Advance or Super Selco. Samples were collected at 2, 5, 10, 15 and 31 DAH to determine dry weight, total length, myotome height and thyroid status. Larvae fed the iodine‐enriched diet had significantly higher weight at 31 DAH and higher levels of whole body iodine concentration, compared to control larvae. At 31 DAH, larvae from the control treatment showed typical goitrous thyroid follicles. Thyroid cells of larvae from this treatment appeared columnar or afollicular, with the colloid partly or completely depleted, representative of hyperplasia (goitre). The lower growth rate in fish larvae from the control treatment was possibly a consequence of the hyperplasia, and the iodine enrichment prevented Senegalese sole larvae from developing goitre. This study demonstrates the importance of iodine enrichment of live feed for fish reared in a recirculation system.     

Examination of a practical method for zinc enrichment of euryhaline rotifers (Brachionus plicatilis)

Larval growth and survival of marine finfish in mass seed production are affected by the nutritional value of live feeds such as rotifers and Artemia. Thus far, many studies have been conducted to develop effective methods for the enrichment of live feeds with essential fatty acids and vitamins. In this study, a practical method for enrichment of rotifers with zinc was investigated. Changes in the concentrations of other minerals when zinc was added to the rotifer-enrichment tanks were also studied. The mineral composition of rotifers and Chlorella after zinc enrichment revealed that the direct addition of zinc to the culture media was not effective because rotifers cannot efficiently accumulate waterborne zinc. The ability of Chlorella to absorb waterborne zinc is much higher than that of rotifers, and hence, zinc was pre-accumulated in Chlorella, which was then fed to the rotifers. The maximum zinc content of the rotifers was 585.0 μg g^? 1 (dry matter) when the rotifers were enriched with zinc alone. This zinc concentration is comparable to that found in natural zooplankton. In rotifers simultaneously enriched with zinc and n?3 highly unsaturated fatty acids (HUFAs), the zinc content increased, but the n?3 HUFA content did not. Therefore, separate enrichment with zinc and fatty acids was adopted. The zinc content of rotifers fed zinc-enriched Chlorella was significantly higher than that of rotifers fed unenriched Chlorella. After zinc enrichment, rotifers were enriched with fatty acids, and the docosahexaenoic acid (DHA) and n?3 HUFA levels in rotifers were higher than the levels obtained after simultaneous enrichment with zinc and fatty acids. With regard to the concentration of other minerals in rotifers after zinc enrichment, the manganese content tended to decrease when the zinc content increased.The results of this study demonstrated that zinc enrichment of rotifers was successfully performed by using microalgae that had accumulated zinc, and the enrichment of rotifers with fatty acids was also achieved after the completion of zinc enrichment and before feeding the larvae. This method could be utilized for the enrichment of zooplankton with other minerals as well.     

Low-temperature preservation (at 4 °C) of marine rotifer Brachionus

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. Müller 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 °C in B. 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 acclimation at 10 °C. (4) The combination of frequent exchange of culture media and acclimation significantly 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.     

Effects of docosahexaenoic acid on growth,survival and swim bladder inflation of larval amberjack ( Seriola dumerili, Risso)

The effect of docosahexaenoic acid (DHA) on the growth performance, survival and swim bladder inflation of larval Seriola dumerili during the rotifer feeding period was investigated in two feeding experiments. Amberjack larvae at 3 day post hatching were fed rotifers enriched with (1) freshwater C hlorella (Chlo), (2) a mixture (2:1, v/v) of Chlo and DHA‐enriched C hlorella (DHA‐Chlo), (3) DHA‐Chlo and (4) DHA‐Chlo and commercial DHA emulsion, in triplicate for 7 days. The average DHA contents of the rotifers were 0.0, 0.4, 1.0 and 1.9 mg g^?1 DM respectively. The survival rate was improved by the enrichment of rotifers with DHA‐Chlo alone, and DHA‐Chlo and emulsion. Growth and swim bladder inflation of fish fed rotifers enriched with DHA‐Chlo were significantly (P < 0.05) improved, however, with increased levels of DHA further improvement was not found. DHA content in the larval whole body proportionally increased with the DHA level in the rotifers. These results suggest that DHA enrichment of rotifers is effective to improve the growth, survival rate and swim bladder inflation of amberjack larvae. The DHA requirement of amberjack larvae is estimated to be 1.5 mg g^?1 on a dry matter basis of rotifers.     

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.     

Improved hatchery‐rearing techniques for juvenile production of blue swimming crab,Portunus pelagicus (Linnaeus, 1758)

The effects of tank colour, larval stocking density, antibiotic administration and water exchange on survival and moulting of blue swimming crab, Portunus pelagicus, were determined. Circular 4‐m³ experimental larval‐rearing tanks were used in triplicate for all treatments. White, dark grey, blue and brown were tested as tank background colours. The stocking densities tested were 10, 20, 40, 60, 80 and 100 larvae L^?1. The effect of oxytetracycline was estimated by comparing a treatment with oxytetracycline to a treatment without oxytetracycline administration. The daily water exchange rates tested were 0%, 25%, 50% and 100% of the tank volume. In all treatments, the larvae were fed with Artemia nauplii, rotifers and encapsulated Spirulina. The highest percentage survival was observed in the dark‐grey tanks when the stocking density of larvae was 20 larvae L^?1. No larva reached the juvenile crab size in white tanks. No significant difference in survival was found between treated and non‐treated larvae with oxytetracycline when the daily water exchange rate was more than 50%.     

Nutritional evaluation of live food organisms and commercial dry feeds used for seed production of amberjack Seriola dumerili

To improve the nutritional quality of live foods and dry feeds ordinarily used for the seed production of amberjack Seriola dumerili, the nutrient contents of rotifers, Artemia nauplii and commercial feeds used in two larval production stations were evaluated. For comparison of the nutrient contents, artificially produced larvae, wild-caught juveniles and wild zooplankton samples were also analyzed. The proportions of 22∶6n-3 in the polar lipid of the cultured larvae increased by feeding the dry feeds. The taurine contents of the cultured larvae reflected the contents of their foods (rotifers<dry feed<Artemia nauplii). The taurine content and the proportion of 22∶6n-3 in Acartia spp. were higher than in foods fed to the larvae. These parameters in the wild juveniles were higher than the cultured ones. The A/E ratios [(each essential amino acid/total essential amino acids)×1000] of the total amino acids of the live foods and dry feeds were similar to those of the cultured larvae, except for the lower ratios of histidine, arginine, threonine and lysine in the live foods. The mucosal folds of the intestine of the cultured larvae did not show typical signs of dietary phospholipid deficiency. These results suggest that requirements of nutrients such as 22∶6n-3 and taurine should be determined for mass production of amberjack seeds.     

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.     

Changes in mineral concentrations in amberjack Seriola dumerili larvae during seed production: high concentrations of certain minerals in rotifers do not directly affect the mineral concentrations in larvae

This study examined the changes in mineral concentrations in amberjack Seriola dumerili larvae during seed production taking into consideration the mineral concentrations of rotifers in the larval rearing tanks (tank rotifers), since the concentrations of certain minerals in tank rotifers have been reported to be very high. In the present study, the concentrations of Ca, Mg, Fe, Zn and Mn in tank rotifers were generally higher than in freshly enriched rotifers. The extent of the increase in tank rotifers varied depending on the mineral, larval production facility and larval production trial. Concentrations of Ca in the larvae increased as they grew, those of P and Mn increased up to ca. 30 days post-hatching (DPH), those of Mg and Fe increased up to ca. 20 DPH and then decreased, and those of Zn continuously decreased through the seed production periods (to ca. 40 DPH). However, there were no clear relationships between the mineral concentrations of the tank rotifers and the larvae. These results indicate that high concentrations of minerals in tank rotifers are not directly reflected in amberjack larvae. This suggests that amberjack larvae maintain their mineral status by controlling the uptake and/or excretion of food minerals.     

Effect of different algae used for enrichment of rotifers on growth, survival, and swim bladder inflation of larval amberjack Seriola dumerili

The effect of algae with different DHA contents used for the enrichment of rotifers on the growth performance, survival, and swim bladder inflation of larval amberjack Seriola dumerili was investigated. Rotifers were enriched with freshwater Chlorella vulgaris containing three levels of DHA (rotifer containing DHA 0.04, 0.60, 1.32?g DHA 100?g^?1 DM) and Nannochloropsis (0.04?g DHA 100?g^?1 DM; 2.54?g EPA 100?g^?1DM). The larvae were fed the enriched rotifers in triplicate from 3?days post-hatch for 7?days in static condition. The same algae used for rotifer enrichment were supplied to the larval tanks. Growth and survival rate of fish fed the rotifers enriched with Nannochloropsis were higher than those of fish fed the rotifers enriched with all three Chlorella treatments. Swim bladder inflation was lowest in fish fed the rotifers enriched with Nannochloropsis. The proportion of EPA was higher in fish fed the rotifers enriched with Nannochloropsis, while that of DHA increased proportionally with the DHA levels in the rotifers enriched with Chlorella. These results suggest that rotifers enriched with Nannochloropsis (EPA-rich rotifers) are effective to enhance growth and survival, but DHA instead of EPA is essential to improve the swim bladder inflation in amberjack larvae.     

Ceramic clay reduces the load of organic matter and bacteria in marine fish larval culture tanks

Ceramic clay has been increasingly used to improve contrast and prey detection in tanks for rearing of fish larvae. In contrast to live microalgae or algae pastes, clay increases turbidity without contributing to the organic matter load. In addition, clay may aggregate and sediment organic matter and bacteria, facilitating its removal. Marine larvae are sensitive to infections by opportunistic bacteria. Fish, algae, and live feed increase the microbial carrying capacity of the rearing water which allow exponential growth of bacteria and favor fast-growing opportunists. Reducing substrate levels by replacing microalgae with clay may reduce bacteria proliferation and benefit larvae. We compared the effects of three rearing regimes including live Isochrysis galbana, Nannochloropsis oculata paste, and ceramic clay on the bacterial community, concentration of organic matter, and growth and survival of Atlantic cod larvae (Gadus morhua L.). The application of clay resulted in reduced substrate levels for bacteria in the rearing water compared to the addition of live algae or algae paste. To some extent, clay aggregated and transported organic matter to the bottom of the larval fish tanks, where it could be effectively removed. Fish tanks receiving clay showed a lower abundance of bacteria in the water than tanks added algae paste or live algae. Fish tanks with algae paste showed a higher abundance of bacteria and a higher share of cultivable bacteria and TCBS counts than the other two treatments. Tanks with live algae showed low relative abundances of opportunistic bacteria and TCBS counts in both water and rotifers. Cod larvae in tanks with clay or live algae initiated exponential growth earlier than larvae in tanks with algae paste. Larvae in tanks receiving clay had significantly higher dry weight than larvae in tanks receiving algae paste at day 5 and 20 post hatching. The survival of larvae in the tanks added clay was variable. Two of the three tanks with clay had significantly higher larval survival than the tanks with live algae or algae paste. However, one tank with clay underwent 100% mortality. It is not possible to conclude whether this was related to the use of clay or an incidental development of a harmful microbial community in this tank. The effects of clay addition on larval performance should be studied further. Clay addition appears to be an easy way to reduce bacterial load during early first feeding of marine larvae without compromising the beneficial effects of turbidity.     

Effect of Rotifer Enrichment on Sunshine Bass Morone chrysops × M. saxatilis Larvae Growth and Survival and Fatty Acid Composition

The effect of enriching rotifer prey with highly unsaturated fatty acids on sunshine bass Morone chrysops × M. saxatilis larval survival and growth from ages 4 to 12 d posthatch was determined. Comparisons were made among larvae fed (1) rotifers cultured with Nannochloropsis paste versus rotifers cultured with Nannochloropsis paste and enriched with Culture Selco 3000; (2) no rotifers versus rotifers cultured with Nannochloropsis paste and enriched with Culture Selco 3000; and (3) rotifers cultured with Nannochloropsis paste and enriched with Culture Selco 3000, rotifers cultured with Nannochloropsis and Pavlova pastes and enriched with Culture Selco 3000, and rotifers cultured with Nannochloropsis paste and enriched with Culture Selco 3000 and Super Selco. The only differences in survival were unfed larvae with practically no survival compared to 55.4% survival for larvae fed rotifers cultured with paste plus Culture Selco 3000. Larvae fed rotifers cultured with paste plus Culture Selco 3000 were longer and had greater condition than those fed rotifers cultured with paste. Additional enrichment with Pavlova sp. or Super Selco had no affect. A canonical analysis of fatty acid contents of diets, rotifers, and fry supported evidence from harvest results. Distances between centroids indicated distinct differences among diets, less distinction among the rotifers, and little difference among fry. Enrichment enhanced growth, but additional enrichment beyond that done during rotifer culture did not increase survival, growth, or condition.     

Effect of light irradiation on dynamics of vitamin A compounds in rotifers and Artemia

ABSTRACT:   The dynamics of vitamin A (VA) compounds in live food during enrichment were examined under different light conditions. Rotifers Brachionus plicatilis and Artemia nauplii ( Artemia ) were enriched with or without 10 mg VA palmitate (VAp) in 1 L of culture medium for 24 h under either bright (2000 lx), or dark (<1 lx) conditions. VAp, retinol (ROH), retinal (RAL) and retinoic acid (RA) contents were analyzed at 0 h (before enrichment) and at 3, 6, 12, 18 and 24 h after the onset of enrichment. Retinoid content in rotifers enriched in darkness was always higher than that enriched under light. VAp content showed two peaks at 3 and 18 h in rotifers enriched in darkness, but it showed one peak at 3 h in rotifers enriched under light. ROH and RA contents increased over the 24-h period in rotifers enriched in darkness, whereas they decreased 12 h onward in rotifers enriched under light. In Artemia , VAp and ROH contents were always higher than when enriched under the bright condition, but their dynamics showed a similar pattern in Artemia enriched under dark and bright conditions.     

Does the presence of microalgae influence fish larvae prey capture?

The green water technique has been widely shown to improve fish larvae growth, survival and feed ingestion. Therefore, fish larvae (Sparus aurata L. and Solea senegalensis Kaup) feeding behaviour was studied through gut content analysis, when using different species of microalgae, as the ‘green water’ technique. Six treatments were used: Stain – food green stain; Tetra – microalgae Tetraselmis chuii; Iso – microalgae Isochrysis galbana; Tetra Sup –T. chuii supernatant (obtained from centrifugation); Phyto – a microalgae paste, Nannochloropsis oculata, (Phytobloom^®); and C water – clear water, as control. At 9, 16 and 23 days after hatching (DAH) for S. aurata, and 4, 9 and 14 DAH for S. senegalensis, 40 unfed fish larvae were transferred to 3 L experimental tanks, filled with the different ‘green water’ technique. Fish larvae were sampled 2 h after being fed with live prey, anaesthetized and fixed in buffered formaldehyde for posterior gut content determination. Feeding was evaluated by the feeding rate, percentage of larvae with prey items in the digestive tract and feeding intensity, number of prey in each larva digestive tract. Fish larvae feeding ability was influenced by the interaction between light conditions and substances provided by the presence of microalgae during fish larvae development. Sparus aurata was more dependent on microalgae addition than S. senegalensis larvae, which may be related to the type of prey, larval behaviour, ontogeny and physiology. The presence of microalgae influenced the selection of larger prey (Artemia over rotifers) by S. aurata aged 23 DAH.     

Effects of diet transition regimen on survival, growth and lipid composition of intensively reared Atlantic cod, Gadus morhua, larvae

Replicated groups of Atlantic cod were rearedfor up to 40 days in 100 l tanks stocked at adensity of 75 eggs l^–1. Larvae weretransferred from rotifers, Brachionusplicatilis, to either fresh-hatched orenriched Artemia nauplii on each of days5, 15 and 25 post-hatch (ph). Rotifers wereprogressively withdrawn over a 5 day period.The type of Artemia offered(fresh-hatched, enriched) did not affectsurvival or growth rates at any of the 3transfer ages. Larvae transferred toArtemia from day 5 ph suffered a highincidence of swimbladder over-inflation andhigh mortality during metamorphosis (< 1%survival to day 36 ph). Cod in the day 15 and day25 transfer groups did not differ significantlyin weight-specific growth rate or size on day40 ph (mean standard length 13.8 mm, dry weight3.8 mg). Highest mean survival rates to day 40ph (18.1%) and lowest mortality followingtransfer to nursery tanks were also observed inthe day 25 transfer groups. Fish that receivedArtemia from day 5 ph containedcirca twice as much total lipid per unit bodyweight and had a 30% higher triacylglycerol(TAG) content compared to all other groups.Ratios of the essential fatty acidsdocosahexaenoic acid (DHA), eicosapentaenoicacid (EPA) and arachidonic acid (ARA) alsodiffered according to age-at-transition.DHA:EPA ratio exceeded 1 only in codtransferred to Artemia on day 25 ph.Based on these findings, it is recommended thatintensively reared Atlantic cod should continueto receive rotifers until completion ofmetamorphosis.