Breeding and larval rearing of the rabbitfish,Siganus guttatus (Bloch)

Females of Siganus guttatus reared to sexual maturity in canvas tanks were induced to spawn by using human chorionic gonadotropin (HCG, Ayerst) at 500 IU/fish or about 2 IU/g body weight. The amount of HCG used depended on the initial mean egg diameter; the smaller the diameter, the more HCG was used. Fish with oocytes characterized by germinal vesicle migration (mean egg diameter ≥ 0.47 mm) spawned without HCG injection. Fertilization and hatching rates for both treated and untreated fish were more than 90%. The larvae were reared to metamorphosis using rotifers from day 2–17, rotifers + newly hatched Artemia nauplii from day 18–20 and rotifers + newly hatched Artemia nauplii + artificial feed from day 21–35. In addition, Isochrysis galbana was introduced to the rearing tanks from day 1–10 and Chlorella sp. and/or Tetraselmis sp. from day 1–35. Survival rates of larvae tended to be lower as the broodstock became older.     

Influence of nitrogen availability on the biochemical composition of three unicellular marine algae of commercial importance

Chaetoceros calcitrans (Paulsen) Takano, Tetraselmis suecica (Kylin) Butch. and Isochrysis galbana Parke were grown in artificial seawater containing either normal (9·8 mg atoms litre^?1) or reduced (0·613 mg atoms litre^?1) nitrogen. When grown in the nitrogen-deficient medium protein decreased and carbohydrate increased in all three species; lipid, however, increased in Chaetoceros and Isochrysis but decreased in Tetraselmis.The biochemical composition of Tetraselmis and Isochrysis sampled during the post-exponential phase of growth from normal medium was similar to that of cells growing exponentially in nitrogen-deficient medium. Salinities of 10–35‰ did not affect protein levels in Tetraselmis or Isochrysis but carbohydrate increased and lipid decreased in Isochrysis over the salinity range. Temperatures of 18–25 °C had little effect on the cell composition of either species.The energy potentially available from a unit volume of Chaetoceros and Isochrysis cells from normal medium was similar to that from cells grown in nitrogen-deficient conditions in both species. Tetraselmis had 34% more energy available when grown in normal compared to nitrogen-deficient medium.     

Environmental persistence of chlorine from prawn farm discharge monitored by measuring the light reactions of photosynthesis of phytoplankton

Chlorine (reactive chlorine: Cl₂+OCl^?) is used as a disinfectant on prawn farms but the environmental effects of discharged chlorine is of environmental concern. Toxicity of chlorine on prawn farm phytoplankton populations was monitored using the pulse amplitude fluorometer technique to measure phytoplankton photosynthesis. The dominant phytoplankton species found in the ponds of a prawn farm in Pang-Nga Province (Thailand) were Chlorella sp. (>95 %), with some Tetraselmis and Chaetoceros. Cells were suspended in clean sea water with (chlorine) of 15, 30, 45, 60, 75 and 90 ppm, respectively, in short-term experiments for 10 min (ST) and for long-term (24 h) exposure. Photosynthesis of Chlorella, Tetraselmis and Chaetoceros in clean sea water was inhibited by 50 % at (chlorine) of 4.68 ± 0.6, 7.26 ± 1.14 and 7.81 ± 0.78 ppm (mean ± SEM), respectively, in ST experiments. The chlorine consuming reactions with the large amounts of dissolved organic matter and ammonia in prawn farm pond water decreases toxicity but would form organochlorines and chloramine. Thiosulphate, often used to neutralise chlorine, was found to be of very limited toxicity to Chlorella in both short-term 1-h and 24-h experiments (up to ≈500 mmol m^?3, 124 ppm). Environmental effects of Chlorine in discharges from ponds are short term. Chlorine quickly disappears in the environment, particularly during daylight and so only has effects close to effluent points. Standard practice was to discharge on a falling tide in daylight. The long effluent channel (1 km) also ensured that very little reactive chlorine reached the estuary.     

The influence of salinity on the production of two commercially important unicellular marine algae

During 1975 and 1976 it was found that lower growth and therefore productivity from 20 l semi-continuous cultures of Isochrysis galbana Parke and Tetraselmis suecica (Kylin) Butch. was related to an increase in salinity from 31 to 36‰ of the natural sea water used in medium preparation. This effect was removed in 1977 by lowering salinity to 25‰ prior to medium preparation. Small-scale trials with Isochrysis in 1977 showed that growth was improved when the salinity was reduced to 28‰. Optimal salinity ranges for growth in medium prepared from artificial sea water were found to be 15–25‰ for Isochrysis and 25–30‰ for Tetraselmis.     

Food ingestion and digestibility of five unicellular algae by 1-day-old Strombus gigas larvae

This work presents food ingestion and digestibility analysis carried out by means of epifluorescence microscopy of 1‐day‐old Strombus gigas (Linnaeus, 1758) larvae fed five different algal cells: Tetraselmis suecica, T. tetrathele, Chlorella keslleri, Chlorella sp. and Chaetoceros cerastoporum. Absolute ingestion and digestion indices (AII and ADI) were used to compare larval feeding behaviour. Differences in efficiency of ingestion and digestion were observed, according to the diet: the highest AII and ADI were observed with T. suecica and T. tetrathele (>90% and 85–88% respectively). With C. cerastoporum and Chlorella sp. these indices were zero. We confirm the use of Tetraselmis as a suitable diet for S. gigas hatchery. On the contrary, Chlorella sp. and C. cerastoporum are not recommended during the early larval stage, due to their non‐ingestion and digestion.     

Mutualism between euryhaline tilapia Sarotherodon melanotheron heudelotii and Chlorella sp.—Implications for nano-algal production in warmwater phytoplankton-based recirculating systems

The West-African euryhaline tilapia, Sarotherodon melanotheron heudelotii shift from visually feeding on zooplankton when juveniles to mostly filter feeding on phytoplankton when adults. When reared using an appropriate ration in intensive aquaculture systems, S. m. heudelotii also consume algal-based detritus, and contribute to sediment mineralization, clean up their environment, and ultimately stimulate and sustain algal growth. We analysed such practical advantages for phytoplankton-based recirculating systems, using S. m. heudelotii and Chlorella sp. as biological material originating from the prototype of such a system operated in Senegal. We performed a 24-h factorial design experiment in 36 tubs, cross-classifying three levels of S. m. heudelotii (fishless control, unfed fish, and fed fish) with four levels of Chlorella initial density.Chlorella overall mean density increased significantly from fishless, to unfed fish, and fed fish treatments, and with Chlorella initial density. S. m. heudelotii did not alter nitrogen nor phosphorus concentrations, only affected by algal initial densities. Most ammonia excreted by fish was probably uptaken by Chlorella. Bacteria-mediated diurnal nitrification was possibly an alternative ammonium loss mechanism at highest oxygen concentrations. Algae were not limited by nitrogen or phosphorus but most likely by low dissolved organic carbon availability. Chlorella differential responses with fed vs. unfed Sarotherodon suggest that CO₂ supplied by heterotrophic S. m. heudelotii respiration played a key role. Observed Chlorella growth rates were similar to the highest rates obtained in algal mass cultures, enriched with CO₂, nitrate and phosphate, under artificial lighting.Our results suggest the existence of a Sarotherodon-Chlorella mutualism in our systems, where S. m. heudelotii provide CO₂, the major limiting factor of Chlorella growth, whereas Chlorella oxygenate and detoxify the water media from ammonia, promoting S. m. heudelotii production. This mutualism could be used to optimize photosynthetic suspended-growth aquaculture systems, particularly in the Tropics where light is abundant and temperature is continuously high.     

Growth, filtration and ingestion rate of the rotifer Brachionus plicatilis fed with large (Asteromonas gracilis) and small (Chlorella sp.) celled algal species

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.     

Development of hatchery technology for the silver pomfret Pampus argenteus (Euphrasen): effect of microalgal species on larval survival

The silver pomfret Pampus argenteus (Euphrasen) is a new candidate for aquaculture and there is not much information available on its larval rearing. Investigations carried out using microalgae alone in the culture system for the initial feeding of the silver pomfret larvae showed that Chlorella, Isochrysis and Nannochloropsis without rotifers are not conducive to the survival of newly hatched larvae. At 6 days after hatching (DAH), a maximum survival of 3% (1.8 ± 1.69%) was observed with Isochrysis followed by Nannochloropsis (0.35 ± 0.21%) and Chlorella (0.25 ± 0.21%). All control larvae died at 6 DAH without microalgae. Further investigations using the above microalgae with rotifers and a mixture of these same microalgae with rotifers showed that significantly higher (P < 0.05) survival could be achieved in the mixture of microalgae with rotifers in the culture system. At 12 DAH, the larval survival was 9.73 ± 1.39% in mixed species of algae compared with that of Isochrysis (6.93 ± 1.86%), Nannochloropsis (6.83 ± 0.61%), Chlorella (5.93 ± 2.76%) and seawater without microalgae or the control (0.73 ± 0.31%). The first incidence of feeding on rotifers at 4 DAH was significantly higher (P < 0.05) in all treatments with microalgae than that of the control. The incidence of feeding in mixed species of algae at 4 DAH (60.0 ± 0.00%) and in Isochrysis (55.0 ± 35.36%) was significantly higher (P < 0.05) than that of Chlorella (40.0 ± 0.00%) and the control (25.0 ± 7.07%). Prey consumption of individual larvae increased significantly (P < 0.01) at 8 DAH compared with that at 4 DAH. During this period, predation on rotifers by larvae was significantly higher (P < 0.05) in mixed species of algae (12.85 ± 5.73 rotifers larva^?1) than that of the control (6.75 ± 1.20 rotifers larva^?1). The fatty acid composition of rotifers used during this investigation shows that significantly higher (P < 0.05) ω3 HUFA was present in rotifers treated with mixed algae plus commercial enrichment media ‘Super Selco’ and ‘DHA Protein Selco’. Rearing of silver pomfret larvae up to the juvenile stage using mixed species of microalgae in the hatchery has been discussed. During 38 days of the larval rearing period, it was possible to achieve 3.6–4.2% larval survival with a mean of 3.9 ± 0.42%, which was considerably higher than in previous attempts (survival up to 1.5%).     

On the grey mullets of the Nigerian coast,prospects of their culture and results of trials

Mullets have so far been recorded in the brackish water areas only and of the 8 species identified, Liza falcipinnis is the most abundant. Mullet fry (mixed species) are available throughout the year but in greater quantities between March and July. It is estimated that enough fry to stock more than 10 000 ha for polyculture can be collected from the coastal areas. With a view to culturing them in fresh water, it has been possible to acclimatize them to fresh water. This offers good prospects of culturing mullets together with common carp, catfish (Chrysichthys nigrodigitatus) and cichlias (Tilapia sp.)Polyculture trials in brackishwater ponds in Lagos indicate that the natural entry of mullet fry with the tide could result in productions of up to 239 kg ha^?1 year^?1 in addition to that of other species, without supplementary feed or fertilizer. Stocking of mullet fry increased the mullet yield. Experiments indicate that supplementary feed also increases both yield and average size. Predators such as Sphyraena sp. reduce mullet population in fish ponds and also their yield.     

Culture of the calanoid copepod Pseudodiaptomus euryhalinus (Johnson 1939) with different microalgal diets

The copepod Pseudodiaptomus euryhalinus was fed 320 cells μL^− 1 of monoalgal cultures of Chaetoceros muelleri, Nannochloropsis oculata, Isochrysis galbana, Tetraselmis suecica, or a commercial frozen concentrate of Tetraselmis sp., and the diet which gave the best production was compared in a second experiment to three mixed diets: C. muelleri:I. galbana supplied in 1:1 and 2:1 cell ratios and C. muelleri:I. galbana:frozen Tetraselmis sp. in 2:2:1 ratio. These gave better results than the cultures of N. oculata, I. galbana, T. suecica and the frozen Tetraselmis concentrate, but the production was similar to that obtained with C. muelleri supplied as a monoalgal diet, showing that the addition of C. muelleri may improve the performance of other monoalgal diets, whereas the addition of other microalgae is unlikely to improve the results obtained when C. muelleri is supplied as a monoalgal diet.     

Food value of Brachionus plicatilis fed three selected algal species as live food for milkfish, Chanos chanos Forsskal, fry production

Abstract. The effects of three selected algal species, Tetraselmis tetrahele, Isochrysis galbana and marine Chlorella sp. on the population growth of Brachionus plicatilis was evaluated after 3, 5 and 7 days of culture. The rotifers fed on T. tetrahele showed superior growth with mean peak density of 92.5 individuals per ml to those fed on I. galbana (48.2 individuals per ml) and Chlorella sp. (47.2 individuals per ml) in 5 days. In another experiment, milkfish. Chanos chanos Forsskal, fry with initial mean body weight and standard length of 6.26 ± 1.07mg and 13.04 ± 1.40mm, respectively, were fed B. plicatilis reared on the three algal species for 30 days. Results showed that growth, measured in terms of gain in weight and length, was significantly different (P > 0.05) among treatments. Fastest growth was obtained in fry fed B. plicatilis cultured on T. tetrahele with mean gains in weight and length of 61.48 ± 8.40mg and 9.37 ± 1.68 mm, respectively, followed by fry fed B. plicatilis reared on I. galbana (43.56 ± 8.35mg and 6.25 ± 0.48mm). Milkfish fry fed B. plicatilis cultured on Chlorella sp. gave the poorest growth with mean gains in weight and length of 11.05 ± 1.82mg and 2.33 ± 0.29mm, respectively. Percentage survival ranged from 93.1 to 95.3 percent and was not significantly different between treatments (P < 0.05). The differences in population growth of B. plicatilis and consequently growth of milkfish fry was almost certainly attributed to the differences observed in the biological values of their algal diet, and in particular their protein and lipid contents. T. tetrahele and I. galbana improved the food value of B. plicatilis as live food for the milkfish fry. Their high dietary value was related to the higher algal protein and fat levels and contents of n-3 HUFA particularly 20:5n-3 and 22:6n-3 compared to B. plicatilis cultured on Chlorella sp. The results of the present study point to T. tetrahele as the most suitable food for the mass culture of the rotifer, B. plicatilis.     

Influence of different diets on the growth,survival, fecundity and proximate composition of brine shrimp Artemia franciscana (Kellog, 1906)

Artemia franciscana was studied under in vitro conditions, and fed with five different microalgae species, two organic diets and one mixed diet to evaluate the nutritional profile and growth performance. The A. franciscana instar‐I nauplii were stocked at a density of 100 per litre of ground borewell water with a salinity of 70 ppt in a plastic container and the culture continued for 12 days. The A. franciscana was fed with five microalgal species, such as Tetraselmis sp., Chaetoceros sp., Isochrysis sp., Thalassiosira sp. and Nannochloropsis sp., and organic diets of rice bran, soybean meal, and a mixture of Tetraselmis sp. and Chaetoceros sp. with rice bran, giving a total of eight experiments. The growth of A. franciscana was measured by length, and was observed to be the greatest (10,850 μm) in the group that was fed the mixed algae combination, and the lowest (7,290 μm) in the group that was fed Nannochloropsis sp. Among the different treatments, the highest survival value of 76% was seen in the group that was fed Chaetoceros sp. The fecundity was higher in A. franciscana that were fed with algae Chaetoceros sp., while the lower rate was observed with the group that was fed Nannochloropsis sp. Analysis of proximate composition showed increased levels in the animals fed with Chaetoceros sp. (lipid, 19.40%; eicosapentaenoic acid, 6.70 mg; docosahexaenoic acid, 10.20 mg; amino acids: proline, 2.06 μg; histidine, 0.77 μg, arginine, 0.65 μg, glycine, 0.80 μg, glutamic acid, 1.75 μg; threonine, 1.42 μg) and the mixed diet (protein, 58.59%; carbohydrate, 21.30%; amino acids: asparagine, 0.90 μg; serine, 1.65 μg; tryptophan, 1.66 μg; leucine, 1.50 μg; phenylalanine, 1.14 μg; valine, 0.66 μg). All components showed the lowest level in the diet fed with Tetraselmis species. These A. franciscana populations showed better survival, higher fecundity and biochemical profiles when cultured with microalgae Chaetoceros sp. These data are useful to improve A. franciscana culture in aquaculture to produce quality cysts and biomass, especially in feeding larvae of marine species.     

Observation of gastric obstruction during early feeding of Arctic charr,Salvelinus alpinus (Salmonidae)

During early feeding of Arctic charr (Salvelinus alpinus) with commercial salmon feed, a proportion (2–14%) of the fry were found to have large particles lodged in the forward part of the alimentary canal. These particles were found to be part of the roughage component of the feed. It is considered that they would have led to the death by starvation of the fry which had ingested them.     

Effects of water quality,antibiotics, phytoplankton and food on survival and development of larvae of Scylla serrata (Crustacea: Portunidae)

Larvae of the portunid crab Scylla serrata were successfully reared using a combination of antibiotics (penicillin-G + polymyxin-B), phytoplankton (Chlorella sp.) and appropriate food (Artemia salina nauplii).Antibiotics enhanced premetamorphic survival of zoeae while leaving rate of zoeal development and success of metamorphosis to megalopa unaltered. Water filtration and ultraviolet sterilization had no significant effect on rates of zoeal survival or development. Although antibiotics did not affect metamorphosis of megalopa to the crab stage, the antibiotic mixture may have been detrimental to survival of megalopae.The presence of Chlorella, unlike antibiotics, left zoeal survival unaffected while stimulating production of megalopae. As with antibiotics, time from hatching to megalopa formation was unaltered by the presence of Chlorella.Survival and development of zoeae varied with type and concentration of food organisms used. Feeding with Artemia nauplii produced highest larval survival and continued development. Rotifers and zooplankton as a food source failed to support zoeal survival to the onset of metamorphosis and failed to enhance survival when fed in combination with Artemia nauplii.A daily optimum food concentration of ten Artemia nauplii per ml was established for zoeal survival, while success of metamorphosis of zoeae to megalopa increased as food concentration increased from 5 to 16 nauplii per ml. Rate of development was comparable in all zoeal feeding experiments.Megalopae survived better at the higher food (Artemia) concentrations used and tended to develop more rapidly to the crab stage at higher food levels.     

On the induced spawning and larval rearing of milkfish,Chanos chanos (Forskal)

A female milkfish, captured at sea, was injected with two hormonal injections of acetone-dried salmon pituitary powder and human chorionic gonadotropin, plus Vitamin B complex. It was stripped, and produced 128,000 ripe eggs with an average diameter of 1.15 mm. Fertilization rate was 38% following artificial fertilization with milt from an uninjected male. A total of 36,000 larvae hatched (74% of fertile eggs) after 26–32 h at 34 ‰ salinity and 27–32°C. The newly hatched larvae measured 3.4 mm in mean total length and possessed a large yolk sac. The mouth of the larvae opened about 54 h after hatching. The larvae were fed with fertilized oyster eggs, rotifers, copepods, brine shrimp, flour and prepared feed, together with Chlorella. A critical period was between the 4th and 6th days with mortality over 80%. The larvae started increasing in length by Day 8, and had the appearance of the wild fry by Day 11. On Day 13 a pigmentation pattern developed and the biggest larva measured 10.0 mm. By Day 18 the larvae measured 12.5 mm, and 14.5 mm by Day 21. A total of 2,859 fry was obtained; the highest larval survival rate obtained from different experimental groups was 46.8%.     

Fatty Acid Composition of Different Microalgae Strains (Nannochloropsis sp., Nannochloropsis oculata (Droop) Hibberd, Nannochloris atomus Butcher and Isochrysis sp.) According to the Culture Phase and the Carbon Dioxide Concentration

This study aimed to evaluate the influence of different volumes of supplemented carbon dioxide. which is a potential donator of carbon atom, on the fatty acid profile of four microalgae strains (Nannochloropsis sp., Nannochloropsis oculata (Droop) Hibberd. Nannochloris atomus Butcher and Isochrysis sp.) currently used to enrich rotifers fed to marine fish larvae during two different phases of growth (logarithmic and stationary). Half of the microalgae were cultured at a low CO₂ concentration (0.5 L/min). corresponding to 1 % the air volume (0.038 L/min per L of culture) and the other half of microalgae were cultured at a high concentration of CO₂ (1.1 L/min), corresponding to 2% the air volume (0.086 L/min per L of culture). The resulting fatty acid profile was species-specific and Nannochloris atomus appeared less suitable for inarine organism feeding because of its high percentage of alpha-linolenic acid which represents the only n-3 PUFA of this alga (28.7%). On the contrary, Isochrysis sp. showed the largest proportions of n-3 PUFA also when maintained in the stationary phase (36.46%). Algae cultures contained higher percentages of n-3 PUFA during the logarithmic phase than in the stationary phase when the proportions of short-chain fatty acids increased. High levels of concentrated CO₂ generally increased the content of long chain fatty acids from 17 carbon atoms onwards. The percentages of total n-3 and n-6 were higher than those recorded at low CO₂ concentration. Similarly, the n-3/n-6 ratio was higher at the maximum CO₂ concentration (logarithmic phase). During stationary phase the difference between the two groups was less apparent than that observed in the logarithmic one. The high CO₂ addition exerted a significant and more favorable influence than the low supplementation on the C18:1, C20:0, C20:4n-6, and C22:6n-3 concentrations in both phases, in all four microalgae strains studied.     

Development of First-Feeding Protocols for Indoor Larviculture of Largemouth Bass (Micropterus salmoides)

Largemouth bass (LMB) Micropterus salmoides fry do not accept prepared diets at first feeding. Fry are initially reared in fertilized ponds on natural live foods until large enough to be feed trained. Unpredictable weather patterns and depletion of natural forages can affect nursery pond survival. A series of experiments was conducted to investigate the use of Artemia nauplii prepared diets and optimal feeding schedules to raise LMB fry from first feeding through habituation to a commercial dry diet. In Studies 1, 2, and 3, swim-up fry were transferred to a recirculating system and stocked into either 3-L (Studies 1 and 2) or 10-L (Study 3) acrylic aquaria. Study 1 screened candidate diets to evaluate whether LMB fry could be transitioned directly to prepared diets or if they required live foods. In Study 2 the optimum duration for feeding live Artemia (1, 2, or 3 weeks) and the appropriate size of commercial diets (<200 or 200–360 μm) were evaluated. Study 3 was designed to identify the best transitional feed. Results from Study 1 indicate that fry fed Otohime-A (<200 μm) and decapsulated Artemia cysts performed better than those fed other diets tested. However, survivals were low (6%–8%) indicating a need for live feed initially. In Trial 2, fry fed live Artemia nauplii for two weeks and then transitioned to a 200–360 μm diet (Otohime-B) performed better than other diet combinations tested. In Study 3, survival was significantly higher in treatments using decapsulated Artemia cysts or Otohime-B as transitional diets between initial live Artemia feeding and trout starter. These data indicate that LMB fry can be successfully raised from first feeding to fully habituated to a commercial trout starter by feeding live Artemia nauplii for two weeks, followed by a gradual transition to either decapsulated Artemia cysts or Otohime-B for one week, then gradually transitioning to trout starter. Surviving fish were easily transitioned to commercial floating feed (Study 4). This protocol yielded survival rates of approximately 70% and may improve the reliability of LMB fingerling production by eliminating the outdoor nursery pond phase.     

Optimisation of larval culture of the mussel <Emphasis Type="Italic">Mytilus</Emphasis><Emphasis Type="Italic">edulis</Emphasis> (L.)

The blue mussel Mytilus edulis is a commercially important species whose fishery and culture generally relies on natural spat collection. Hatchery-production could provide an alternative source of seed, enabling reliable expansion of the industry. Mussel spawning and larval rearing trials were carried out to optimise elements of hatchery production. Culturing fertilised eggs at low density (20–200 eggs cm⁻²) rather than high density (400–720 eggs cm⁻²) significantly improved the quality of first veliger larvae and differences in this improvement were evident between the eggs from different females (maternal effects). Veliger larval growth at 17 or 21°C was significantly faster than growth at 14°C. Feeding veliger larvae an identical total ration either daily or at 2–3 day intervals did not significantly affect their growth. Different microalgal diets (1: Isochrysis sp. (clone T-ISO), 2: Chaetoceros calcitrans forma pumilus, 3: C. muelleri, 4: mixed Isochrysis sp. (clone T-ISO) and C. calcitrans f. pumilus, and 5: mixed Isochrysis sp. (clone T-ISO) and C. muelleri) were tested on veliger larval growth and mixed diets outperformed single-species diets.     

Dealing with the presence of the ciliate Euplotes sp. in cultures of the copepod Acartia tonsa

Ciliates in live feed cultures can be a pest that lower production yields. This could dramatically affect the management and success of copepod cultures. In this study, we investigated the effect of the ciliate Euplotes sp. on egg production, specific egg production and egg hatching success of Acartia tonsa fed with Rhodomonas salina. We found that at a concentration of 2 cells ml^?1, Euplotes sp. had no effect on the production and hatching success of eggs but increased/decreased the mortality/quality of non-subitaneous eggs. Euplotes sp. had a good fatty acid profile containing high proportion of unsaturated fatty acids, but the amount of fatty acids compared to their carbon weight was very low and, therefore, it was considered as a poor food source. We propose a short-term interruption of food supply to copepod cultures in order to mitigate bloom formation of ciliates. This will force copepods to feed on them actively as prey and therefore decrease their long-term negative effects.     

Mutualism between euryhaline tilapia Sarotherodon melanotheron heudelotii and Chlorella sp.—Implications for nano-algal production in warmwater phytoplankton-based recirculating systems

The West-African euryhaline tilapia, Sarotherodon melanotheron heudelotii shift from visually feeding on zooplankton when juveniles to mostly filter feeding on phytoplankton when adults. When reared using an appropriate ration in intensive aquaculture systems, S. m. heudelotii also consume algal-based detritus, and contribute to sediment mineralization, clean up their environment, and ultimately stimulate and sustain algal growth. We analysed such practical advantages for phytoplankton-based recirculating systems, using S. m. heudelotii and Chlorella sp. as biological material originating from the prototype of such a system operated in Senegal. We performed a 24-h factorial design experiment in 36 tubs, cross-classifying three levels of S. m. heudelotii (fishless control, unfed fish, and fed fish) with four levels of Chlorella initial density.Chlorella overall mean density increased significantly from fishless, to unfed fish, and fed fish treatments, and with Chlorella initial density. S. m. heudelotii did not alter nitrogen nor phosphorus concentrations, only affected by algal initial densities. Most ammonia excreted by fish was probably uptaken by Chlorella. Bacteria-mediated diurnal nitrification was possibly an alternative ammonium loss mechanism at highest oxygen concentrations. Algae were not limited by nitrogen or phosphorus but most likely by low dissolved organic carbon availability. Chlorella differential responses with fed vs. unfed Sarotherodon suggest that CO₂ supplied by heterotrophic S. m. heudelotii respiration played a key role. Observed Chlorella growth rates were similar to the highest rates obtained in algal mass cultures, enriched with CO₂, nitrate and phosphate, under artificial lighting.Our results suggest the existence of a Sarotherodon-Chlorella mutualism in our systems, where S. m. heudelotii provide CO₂, the major limiting factor of Chlorella growth, whereas Chlorella oxygenate and detoxify the water media from ammonia, promoting S. m. heudelotii production. This mutualism could be used to optimize photosynthetic suspended-growth aquaculture systems, particularly in the Tropics where light is abundant and temperature is continuously high.