Food For Marine Fish Larvae Research Articles

Suitable algal species and density for the culture of copepod Gladioferens imparipes as a potential live food for fish larvae

Four algal species (Isochrysis galbana, Chaetoceros muelleri, Tetraselmis suecica and Nannochloropsis oculata) were tested experimentally as food for the calanoid copepod Gladioferens imparipes, which could be a potential food for marine fish larvae. Each of the algal species was used at four separate concentrations (5 × 104, 1 × 105, 2 × 105 and 4 × 105 cells/ml). The results illustrated that I. galbana and C. muelleri were the most suitable diets for the copepod species, promoting high survival of the adults and shortening the maturation time. With both algal species, intensive successful rearing of nauplii to mature adults was conducted at all concentrations of the algal species, resulting in high number of ovigerous females. Meanwhile, I. galbana was the best diet enhancing the production of egg sac in the cultivated copepod. In addition, the fatty acids in the copepod species were affected by the algal diets, resulting in variable amounts of the HUFA (DHA, EPA and ARA) in the copepod relative to the algal diets.

Rotifer resting eggs: An alternative for rotifer mass cultures in fish farms – Lessons from a comprehensive study on production, storage and hatching of resting eggs

Rotifers of the Brachionus plicatilis complex species serve as the first live food for marine fish larvae. The essential daily supply of rotifers depends on a successful culture of billions of rotifers, as there are no current alternatives for this live food in the large scale production of farmed fish. This problem is not faced with Artemia, the second source of live food, as they are supplied as cysts and hatched according to demand. Rotifers produce resting eggs (RE) that can be stored for long periods of time and hatched when needed, but their use in aquaculture is limited, despite great advantages. Unlike Artemia cysts which are harvested from natural sources or salt works, rotifer RE originate from cultures. A systematic and comprehensive study was carried out to identify the main factors affecting RE production, storage and hatching, with the aim of increasing the efficiency and reducing the costs of production, thus facilitating their wider use in hatcheries.The current study was performed with a clone displaying high propensity towards RE production. RE production was affected by the food type, with a 2–5 fold difference between Nannochlorosis sp. from different sources, at optimal feeding regimes. We uncovered a central role for lipids in promoting RE production. Remarkably, addition of a lipid enriched solution to yeast, increased the number of RE by 10.4-fold, reduced the percent of damaged RE by 5.8-fold and production was similar to one type of algae. The food type did not affect either the length of the obligatory dormant period nor the hatching performance. RE started to hatch at 22–35 days after their formation but the peak was reached after ~44–62 days. RE that were dried close to the time of their formation did not hatch and the hatching potential was gradually obtained towards the end of the obligatory period. Wet RE stored for 2–65 months at 24-26 °C, exhibited a similar hatching performance. Dried RE, however, could be stored for only ~9 months at the same conditions, but for longer periods at 4 °C. Rotifers that hatched from RE can serve for mass production as RE production in these cultures accounted for 4.5% of the total number of females. An automated continuous culture system is proposed and discussed. The current study also provides novel insights into biological attributes on the production and survival of RE, as an important component of the natural food web in the aquatic environment.

Изменчивость размерных характеристик и выживаемости науплиусов крымских артемий Artemia spp. (Branchiopoda: Anostraca) при питании микроводорослями разных видов

Науплиусы жаброногих рачков Artemia spp. (Branchiopoda: Anostraca) ― один из основных видов живых кормов, применяемых при культивировании личинок морских рыб. Для улучшения биохимического состава артемий их насыщают специализированными искусственными смесями или микроводорослями, содержащими незаменимые для личинок рыб компоненты. Размеры, скорость роста и выживаемость науплиусов (N) и метанауплиусов (MN) артемии могут иметь большое значение при их использовании в качестве живого корма. Цель настоящей работы ― выполнить сравнительный анализ размерных характеристик и выживаемости науплиусов крымских артемий производства компании Artemia cysts при питании разными видами микроводорослей. Науплиусы артемии получили в соответствии с общепринятой методикой. В качестве корма использовали следующие виды микроводорослей: Isochrysis galbana, Prorocentrum micans, Gymnodinium wulffii, Prorocentrum cordatum, Tetraselmis suecica, Phaeodactylum tricornutum. Средний диаметр сухих цист артемий составил 0,230 мм. Средние значения длины и ширины ортонауплиусов артемий ― 0,473 и 0,150 мм соответственно. Односуточные MN, питавшиеся T. suesica, имели достоверно меньшие средние значения длины [(0,698 ± 0,014) мм], чем MN, питавшиеся I. galbana, P. micans, G. wulfii и Ph. tricornutum (P < 0,05). Двух- и трёхсуточные MN, питавшиеся I. galbana, имели достоверно бόльшие средние значения длины и ширины (двухсуточные ― 1,19 и 0,324 мм; трёхсуточные ― 1,53 и 0,47 мм соответственно), чем MN, питавшиеся Ph. tricornutum, T. suesica, P. micans и P. cordatum. Среди всех метанауплиусов, насыщавшихся микроводорослями, минимальные средние значения длины имели MN, питавшиеся P. cordatum. Выживаемость метанауплиусов при насыщении P. cordatum, P. micans и T. suecica была максимальной (выше 95 %). Сочетание небольших размеров и высокой выживаемости метанауплиусов, питавшихся P. cordatum (микроводоросль со значительным содержанием докозагексаеновой и эйкозапентаеновой кислот), предполагает их использование в качестве перспективного живого корма для личинок морских рыб.

Selection of Copepods as Live Food for Marine Fish Larvae Based on Their Size, Fecundity, and Nutritional Value

Copepods are a major food source for marine fish larvae in nature. Many studies on copepods culture have been conducted to develop a new live food for the seedling production of marine fish larvae. But fish farmers still depend on rotifer and Artemia nauplii. This study was carried out to find suitable copepods as live food for the larvae in hatchery. Eight species of copepods (1 calanoid, 2 cyclpoid, 5 harpacticoid) that were fed Isochrysis galbana were examined in terms of the size of nauplii, fecundity, amino acids, and fatty acids contents. These species were divided into small (nauplii length 46-86 <TEX>${\mu}m$</TEX>) and large (nauplii length 120-188 <TEX>${\mu}m$</TEX>) size group. Nitokra spinipes in the small group and Tigriopus japonicus in the large group showed the highest fecundity with 151.1 and 139.6 nauplii production per gravid female, respectively. With regard to nutrients, essential amino acids were the highest with 21.2% in cyclopoid Paracyclopina nana in the small group and n-3 HUFA were the highest in calanoid Pseudodiaptomus inopinus (8.5 <TEX>${\mu}g/mg$</TEX>) in the large group and P. nana (8.8 <TEX>${\mu}g/mg$</TEX>). In terms of the size, fecundity, and nutritional value of copepods examined in this study, N. spinipes and P. nana seem to be suitable copepod species to develop as a new live food for small mouth fish larvae.

Climate change and the performance of larval coral reef fishes: the interaction between temperature and food availability.

Climate-change models predict that tropical ocean temperatures will increase by 2-3°C this century and affect plankton communities that are food for marine fish larvae. Both temperature and food supply can influence development time, growth, and metabolism of marine fishes, particularly during larval stages. However, little is known of the relative importance and potential interacting effects of ocean warming and changes to food supply on the performance of larval fishes. We tested this for larvae of the coral reef anemonefish, Amphiprion percula, in an orthogonal experiment comprising three temperatures and three feeding schedules. Temperatures were chosen to represent present-day summer averages (29.2°C) and end-of-century climate change projections of +1.5°C (30.7°C) and +3°C (32.2°C). Feeding schedules were chosen to represent a reduction in access to food (fed daily, every 2 days, or every 3 days). Overall, larvae took longer to settle at higher temperatures and with less frequent feeding, and there was a significant interaction between these factors. Time to metamorphosis was fastest in the 30.7(o)C and high food availability treatment (10.5 ± 0.2 days) and slowest in the 32.2(o)C and low food availability treatment (15.6 ± 0.5 days; i.e. 50% faster). Fish from the lower feeding regimens had a lower body condition and decreased survivorship to metamorphosis. Routine oxygen consumption rates were highest for fish raised at 32.2°C and fed every third day (162 ± 107 mg O2 kg(-1) h(-1)) and lowest for fish raised at 29.2°C and fed daily (122 ± 101 mg O2 kg(-1) h(-1); i.e. 35% lower). The elevated routine oxygen consumption rate, and therefore greater energy use at higher temperatures, may leave less energy available for growth and development, resulting in the longer time to metamorphosis. Overall, these results suggest that larval fishes will be severely impacted by climate-change scenarios that predict both elevated temperatures and reduced food supply.

Preserved copepods as a new technology for the marine ornamental fish aquaculture: A feeding study

The aim of this study was to evaluate the potential use of preserved copepod as prey in Amphiprion clarkii larviculture. After hatching, A. clarkii larvae were divided in three experimental groups for feeding studies as follows: group A (control group) fed rotifers ( Brachionus plicatilis) followed by Artemia nauplii; group B fed a mixed diet of rotifers- Artemia salina nauplii and preserved copepods and group C fed preserved copepods solely. In this study we observed a positive effect of feeding preserved copepods in A. clarkii larviculture as a supplement food to the traditional diet based on rotifers and Artemia nauplii. In group B larvae, fed a combination of rotifers/ Artemia and copepods, a significant increase of insulin like growth factor I and II, peroxisome proliferator activated receptor α−β and thyroid receptor α and β gene expression together with a significant decrease of myostatin gene expression was evidenced by real time PCR compared to the other experimental groups. In this same group we also observed the best results in terms of growth (total length and weight) and survival. These preserved copepods may be considered a suitable food for marine fish larvae larviculture when used as a supplement to the traditional diet based on rotifers and Artemia nauplii.

Choosing an Appropriate Live Feed for Larviculture of Marine Fish

FA167, a 7-page illustrated fact sheet by Cortney L. Ohs, Eric J. Cassiano, and Adelaide Rhodes, discusses the pros and cons of using rotifers, brine shrimp, and copepods as live food for marine fish larvae. Includes references. Published by the UF Program in Fisheries and Aquatic Sciences, December 2009. FA167/FA167: Choosing an Appropriate Live Feed for Larviculture of Marine Fish (ufl.edu)

Effects of nauplial density, product concentration and product dosage on the survival of the nauplii and EFA incorporation during Artemia enrichment with liposomes

In order to determine an optimal enrichment protocol with krill phospholipid liposomes, three different experiments were carried out to evaluate the effects of nauplial density, the concentration of liposome, and the number of doses delivered to the nauplii on the survival and the essential fatty acid (EFA) bioencapsulation in Artemia nauplii. No survival differences were found between the different liposome treatments and the control nauplii enriched with a commercial emulsion. This result confirms that previously described mortalities during Artemia enrichment with liposomes can be minimized and controlled. On the other hand, the EFA incorporation obtained from the three experiments indicates that maximal bioencapsulation is achieved when incubations are carried out under nauplial densities of 300 nauplii ml − 1 , where liposomes are dispensed in a single dose at the beginning of the incubation yielding a concentration of 0.5 g l − 1 . These findings complete those obtained in two preliminary studies, and propose a well defined enrichment protocol with krill liposomes as an alternative complementary method to improve the nutritional value of the Artemia nauplii used as food for marine fish larvae.

Culture experiments with Oithona oculata Farran, 1913 (Copepoda: Cyclopoida), and its advantages as food for marine fish larvae

Culture experiments were made with Oithona oculata Farran, 1913, a coastal water copepod, at Tunas de Zaza and Santa Cruz del Sur, Cuba. A 1 1/2-year semicontinuous experimental-scale polyculture with the rotifer Brachionus rotundiformis (type “S”) in outdoor tarpaulin 2.5-m 3 tanks was established, with Nannochloropsis oculata (20×10 6 cells ml −1) and baker's yeast (1–2 g/10 6 rotifers day −1) as food, reaching a mean density of 5 copepods ml −1 and a maximum density of 8 copepods ml −1, with a daily harvest of 25% of the total volume. A 1-year batch-culture pilot-scale system was also established in indoor concrete 20-m 3 tanks using N. oculata (8–20×10 6 cells ml −1) as food, reaching a mean density of 7 copepods ml −1 and a maximum density of 10 copepods ml −1. Copepod monocultures maintained in polycarbonate 1000-l outdoor tanks were fed a mixture of five species of microalgae ( Chaetoceros ceratosphorum, Tetraselmis tetrathele, Chlorella spp., Dunaliella tertiolecta and N. oculata) at an average density of 2×10 6 cells ml −1. In these nonaerated cultures, final concentrations of 13 copepods ml −1 were obtained in 15-day cultures. Recommendations for improving pelagic copepod culture are presented and their advantages as live food for rearing marine fish larvae are analyzed.

Preparation of Salmon Roe Polar Lipid Concentrate as an HUFA Enricher of Artemia Nauplii

Polar lipids (PL) concentrate was prepared from total lipids (TL) of salmon roe in order to use for highly unsaturated fatty acids (HUFA) enricher of Artemia nauplii, an important live food for marine fish larvae. The PL were concentrated by a solvent partition procedure using a solvent system of equilibrated hexane, ethanol and water. Starting with 120 g of TL, the solvent partition procedure resulted in 29.3 g (27.2 %) of the salmon roe PL concentrate. Major components of the concentrate were phosphatidylcholines (PC; 80.0 %), phosphatidylethanolamines (PE; 7.0 %), and phosphatidylinositols (PI; 5.5 %). Lesser amounts of free fatty acids, sterols and monoacylglycerols were also found in the PL concentrate. Fatty acid analysis revealed the contents of docosahexaenoic acid (DHA; 26.9 %), icosapentaenoic acid (IPA; 14.2 %), and arachidonic acid (AA; 2.4 %). PC and PE isolated from the concentrate were rich in DHA and IPA, whereas PI were rich in AA. The salmon roe PL concentrate appeared to have a potential as an effective HUFA enricher of Artemia nauplii. The solvent partition procedure seems to be useful for convenient preparation of such fish roe PL concentrate.

해산 자치어의 먹이생물로써 섬모충 Euplotes sp.의 평가

This study was carried out to evaluate the ciliates Euplotes sp. as a live food for marine fish larvae. The ciliates and the rotifers Brachionus plicatilis, which were cultured with the baker's yeast Saccharomyces cerevisiae and the <TEX>$\omega$</TEX>-yeast emulsified with cuttle fish liver oil, were supplied to the larvae of flounder Paralichthys olivaceus and grouper Epinephelus akaara. Considering the size difference between the ciliates 68 <TEX>$\cdot$</TEX> 7 <TEX>$\mu$</TEX>n and the rotifers 160 <TEX>$\cdot$</TEX> 20 <TEX>$\mu$</TEX>n, the rotifers and ciliates were supplied to the larvae tank with the density of 2 inds./mL and 20 inds./mL, respectively. The survival rate and growth in length of the flounder larvae fed on rotifer were significantly higher than those on Euplotes sp.. In grouper larvae which have a small mouth diameter, even the survival rate of the larvae fed on the ciliates was better than that on the rotifers, it was very low less than <TEX>$20\%$</TEX>. Therefore, Euplotes sp. seem to be incongruent as a live food for marine fish larvae.

General Method for the Production of Developmentally-Arrested Bivalve Trochophore Larvae as a Potential Food for Marine Fish Larvae

Bivalve trochophore larvae are of an appropriate size (40-60 μm) for first-feeding marine fish larvae. Unfortunately, the trochophore stage is of short duration and the next stage develops a shell, which may hinder consumption and digestion by larvae. A general method from reviewed literature and the author's experience for arresting development at, or prior to, the trochophore stage by genetic modification is presented. Briefly, bivalve sperm are exposed to ultraviolet radiation (254 nm) for a short duration before being used to inseminate the eggs. Ultraviolet radiation alters the sperm DNA structure and results in developmental arrest at, or prior to, the trochophore stage thereby extending the useful life of the trochophore as a live food. The general utility of the method is that it is easy, inexpensive, and can be used on any bivalve species in which sperm or eggs are retrievable and can be kept viable in vitro.

Positional distribution of highly unsaturated fatty acids in triacyl-sn-glycerols of Artemia nauplii enriched with docosahexaenoic acid ethyl ester.

This paper presents the positional distribution of fatty acids in triacyl-sn-glycerols (TAG) of Artemia nauplii used in aquaculture as a live food for marine fish larvae. The nauplii were enriched with docosahexaenoic acid (DHA) ethyl ester (EE) in the form of gelatin-acacia microcapsules for 4, 18, and 24 h. TAG of the initial, enriched, and unenriched Artemia nauplii were subjected to stereospecific analysis. A remarkable increase of DHA content in the enriched Artemia TAG confirmed the view that DHA-EE is effectively assimilated and incorporated into the TAG fraction of Artemia nauplii. TAG of the nauplii enriched with 25 mg/L of DHA-EE contained DHA at concentrations of 5.9-6.8, 4.3-6.0, and 14.3-22.3 mol% in the sn-1, sn-2, and sn-3 positions, respectively. When the nauplii were enriched with 100 mg/L of DHA-EE, proportions of DHA in the sn-1, sn-2, and sn-3 positions were 5.2-8.6, 3.9-6.0, and 12.2-25.4 mol%, respectively. In all of the enriched Artemia, DHA was preferentially located in the sn-3 position followed in sequence by the sn-1 and sn-2 positions. The lower content of DHA in the sn-1 and sn-2 positions was consistent with low content of this acid in 1,2-diacyl-sn-glycerophospholipids. When fish larvae are reared on Artemia nauplii enriched with EE-type DHA oil, the larvae feed on DHA esterified in TAG with a positional distribution pattern similar to that of marine mammals (sn-3 >> sn-1 > sn-2) rather than that of fish or marine invertebrates (sn-2 >> sn-3 > sn-1).

Biology of Moina mongolica (Moinidae, Cladocera) and perspective as live food for marine fish larvae: review

Moina mongolica, 1.0-1.4 mm long and 0.8 mm wide, is an Old World euryhaline species. This paper reviewed the recent advances on its autecology, reproductive biology, feeding ecology and perspective as live food for marine fish larviculture. Salinity tolerance of this species ranges from 0.4–1.4‰ to 65.2–75.4‰. Within 2–50‰ salinity, Moina mongolica can complete its life cycle through parthenogenesis. The optimum temperature is between 25 ◦ C and 28 ◦ C, while it tolerates high temperature between 34.4 ◦ C and 36.0 ◦ C and lower temperature between 3.2 ◦ C and 5.4 ◦ C. The non-toxic level of unionised ammonia (24 h LC50 )f orM. mongolica is < 2.6 mg NH 3–N l −1 . Juvenile individuals filter 2.37 ml d −1 and feed 9.45×10 6 algal cells d −1 , while mature individuals filter 9.45 ml d −1 and consume 4.94×10 6 algal cells d −1 .A t 28 ◦ C, M. mongolica reaches sex maturity in 4 d and gives birth once a day afterward; females carry 7.3 eggs brood −1 and spawn 2.8 times during their lifetime. A variety of food can be used for M. mongolica culture including unicellular algae, yeast and manure, but the best feeding regime is the combination of Nannochloropsis oculata and horse manure. Moina mongolica reproduces parthenogenetically during most lifetime, but resting eggs can be induced at temperature (16 ◦ C) combined with food density at 2000– 5000 N. oculata ml −1 . The tolerance to low dissolved oxygen (0.14–0.93 mg l −1 ) and high ammonia makes it suitable for mass production. Biochemical analyses showed that the content of eicospantanoic acid (20:5ω3) in M. mongolica accounts for 12.7% of total fatty acids, which is higher than other live food such as Artemia nauplii and rotifers. This cladoceran has the characteristics of wide salinity adaptation, rapid reproduction and ease of mass culture. The review highlights its potential as live food for marine fish larvae.

The effects of temperature and dietary fatty acids on the fatty acid composition of harpacticoid copepods, for use as a live food for marine fish larvae

Two marine harpacticoid copepod species, Amonardia sp. and Tisbe sp., were isolated from plankton collected near Halifax, Nova Scotia. The effect of two algal diets ( Dunaliella tertiolecta and Isochrysis galbana) on the essential fatty acid (EFA) composition of Amonardia for use as an alternative live food for coldwater marine finfish larvae was evaluated. This copepod was able to synthesize a significant amount of the EFAs, 20:5 n−3 (eicosapentaenoic acid; EPA, 0.5%) and 22:6 n−3 (docosahexaenoic acid; DHA, 13.6%) from shorter chain n−3 polyunsaturated fatty acids (PUFAs), when fed the algae D. tertiolecta. The marine harpacticoids, Amonardia sp. and Tisbe sp., were fed the same algal diet ( I. galbana) and cultured at 20, 15 and 6°C. The temperature effect on n−3 EFA for both species showed the same general pattern. The concentration of n−3 HUFA decreased in the following order: 6°C>20°C>15°C. The EFA values for marine fish larvae of two cultured harpacticoid copepods, Tisbe sp. and Amonardia sp., are compared with that of wild zooplankton and trochophore larvae of the mussel Mytilus edulis

Effects of Rotifer and Artemia Fatty‐Acid Enrichment on Survival, Growth and Pigmentation of Summer Flounder Paralichthys dentatus Larvae

Abstract— Enrichment of live food for marine fish larvae with highly unsaturated fatty acids (HUFA) has been shown to improve survival, growth and stress resistance in many species and to decrease pigmentation abnormalities in flatfish. In order to aid the developing summer flounder industry, we conducted an experiment in which summer flounder larvae were fed diets differing in HUFA composition to determine whether enrichment with a commercially available product would increase survival and growth and reduce the incidence of abnormal pigmentation. We also examined whether growing unenriched rotifers on different species of algae would affect the survival, growth and pigmentation of the flounder larvae to which they were fed. Growth of summer flounder larvae was significantly better when they were fed HUFA‐enriched Mtifers and Artemia rather than unenriched and, among the unenriched treatments, was significantly better when the larvae were fed rotifers raised on Isochrysis galbana rather than on Tetraselmis suecica. The percentage of larvae that failed to complete metamorphosis during the experiment was significantly higher in the unenriched treatments than in the enriched treatments. Neither survival nor percentage of individuals with pigmentation abnormalities were significantly different among the treatments.

The effects of dietary fatty acids on the fatty acid composition of the harpacticoid copepod, Tisbe sp., for use as a live food for marine fish larvae

The marine harpacticoid copepod Tisbe sp. was isolated from plankton collected near Halifax, Nova Scotia and raised in the laboratory for over 20 generations. The effects of feeding various algal ( Chaetocerus calcitrans, Dunaliella tertiolecta, and Isochrysis galbana) and baker's yeast diets on the nutritional value, or essential fatty acid (EFA) composition, of the copepod for use as an alternative live food for cold-water marine finfish larvae was evaluated in this study. The copepod was able to synthesize a significant amount of the EFA's, 20:5 n−3 (EPA) and 22:6 n−3 (DHA) from shorter chain n−3 polyunsaturated fatty acids, when fed the algae D. tertiolecta (6.2% EPA, 12.4% DHA) or baker's yeast (12.4% EPA, 28.4% DHA) which are deficient in these EFA's. The copepod also maintained a consistently high DHA:EPA ratio (>2) when fed each of the dietary treatments.

Production and use of copepods in marine fish larviculture

Batch and continuous cultures of the harpacticoid copepod Tisbe holothuriae have been run for numerous generations in the laboratory at the North Sea Centre and the harvested nauplii used as food in preliminary trials with first-feeding turbot ( Psetta maxima syn. Scophthalmus maximus). The naupliar swimming behaviour in terms of vertical distribution in a typical fish larval tank and the use of T. holothuriae nauplii as live food for first-feeding turbot larvae were investigated. It was possible to cultivate harpacticoid copepods in shallow trays or in continuous bioreactors with large area substratum. Two such systems were compared in terms of area productivity and the use of ammonia excretion as a means for controlling feeding of the copepods was investigated. Finally, the potential benefits of the use of copepods as live food for marine fish larvae are discussed.

Feeding behaviour and prey size selection of gilthead seabream, Sparus aurata, larvae fed on inert and live food

Prey selection shortly after the onset of feeding by laboratory-reared gilthead seabream, Sparus aurata L., larvae was studied using larvae fed on two types of microcapsule (hard- and soft-walled) having diameters ranging from 25 to 300 μm. Preferences between inert food and live prey (rotifers and Artemia sp. nauplii) were also studied. Seabream larvae were able to ingest inert food from first feeding. Larvae of all size classes ingested hard microcapsules with diameters in the range 25 to 250 μm. However, larvae with a total length (TL) below 4 mm preferentially selected particles 25 to 50 μm in diameter, larvae of TL 4 and 5 mm preferred particles 51 to 100 μm in diameter, while larvae above 5 mm TL preferred particles 101 to 150 μm in diameter. With soft microcapsules, larvae always preferred particles larger than in the previous case, and above 4.5 mm TL they preferentially selected particles 201 to 250 μm in diameter. In addition, the gradual increase of preferred diameters with increasing TL was more pronounced when larvae were increasing TL was more pronounced when larvae were fed on soft particles. Mean values for prey width/mouth width ratios were approximately 0.24 and 0.30 when larvae were fed on hard-walled and soft-walled microcapsules, respectively, irrespective of the absolute value of larval length. When a mixed diet of live and inert food items was offered, live prey were always preferentially selected, even if the prey width/mouth width ratio was apparently not favourable. Only a physical constraint such as excessive prey width could counter this preference for living prey vs inert microcapsules. These results contribute to our knowledge in larval feeding behaviour, especially in the presence of inert food, and represent a fundamental step in developing prepared food for marine fish larvae.

Factors affecting survival of rotifers ( Brachionus plicatilis O.F. Müller) at 4°C

The possibility of maintaining rotifers ( Brachionus plicatilis O.F. Müller) at 4°C for extended periods of time at high densities and at a low cost was examined. It was found that the dynamic processes involved in the maintenance of a rotifer population (hatching and production of eggs) continue to operate at 4°C, but their rate is reduced to one-tenth of that occurring at 25°C. The survival of rotifers and the percent of eggs carried by them were affected by the frequency of changing the culture media, the salinity in which they were cultured, and the amount of food provided and its type (algae, yeast or Topal). Higher survival rates were observed in rotifers maintained in the dark. Statistical analysis revealed that in most cases, the time spent at 4°C significantly affected both survival and the percent of eggs. On several occasions, time interacted with the tested effect, that is, there were differences in the direction of the trend in time between the tested groups. In such a case, the contribution of each of the studied effects could not be evaluated over the total period of the experiments. It had to be analysed separately for each of the observation days; the most relevant being the last day of the experiment. Results of the present research indicate that the cheapest system would involve maintaining rotifers (at least 1000 ml −1) cultured in 10‰ seawater at 4°C with yeast as food. Media would have to be changed every 4–8 days, and the cultures should be maintained in the dark. These rotifers may be used directly, following proper enrichment with unsaturated fatty acids, as food for marine fish larvae, or alternatively to initiate new cultures. The present paper proposes a new method for the preservation of rotifers for periods extending to days or weeks. This would allow more flexibility in managing the supply and demand in a marine hatchery. Alternatively, stored rotifers could be distributed from one main location to small hatcheries or other users lacking facilities for culturing rotifers.