Long‐chain PUFA enrichment in microalgae and metabolic dynamics in Tapes philippinarum larvae

The possibility of increasing n‐3 and n‐6 long‐chain polyunsaturated fatty acids (PUFA) content in microalgal mixtures used to feed Tapes philippinarum larvae was explored by lowering culture temperature from 26 to 14 °C. Although fatty acid composition of different microalgal species has a genetic basis, the algal cultures grown at 14 °C significantly increased the content of long‐chain n‐3 PUFA in Isocrysis galbana and in Thalassiosira pseudonana, while in Tetraselmis tetrathelo, the PUFA increase only involved shorter chain PUFA, namely 16:4n‐3 and 18:4n‐3. However, larvae fed on the PUFA enriched microalgal mixture did not show improvements in growth and survival performances with respect to the control group fed the microalgal mixture grown at 26 °C. From a biochemical perspective, two key aspects emerged from the results: (i) clam larvae have adequate biotransformation and selection skills to adjust fatty acid profile to their requirements as they can even modulate the incorporation of essential long‐chain PUFA as 20:5n‐3 and 22:6n‐3 when the dietary supply exceeds the physiological requirements; (ii) bivalve can biosynthesize non‐methylene‐interrupted dienoic (NMID) fatty acids as confirmed by the constancy of relative proportion with larvae growth in spite of the NMID fatty acid absence in the diet.     

Changes in oil content,lipid class and fatty acid composition of the microalga Chaetoceros calcitrans over different phases of batch culture

The diatom Chaetoceros calcitrans is a microalgal species used as food for larva in aquaculture for many species worldwide. Chaetoceros calcitrans is an important source of omega 3 long chain (C ≥ 20) polyunsaturated fatty acids (n‐3 LC PUFA), chiefly eicosapentaenoic acid (EPA, 20:5n‐3). This article reports lipid content, lipid class composition and fatty acid profiles of each lipid class during the growth cycle of batch cultures of C. calcitrans. Total lipid content and the concentration of neutral lipid were highest in the late stationary growth phase (day 12). However, the amount of EPA was highest during the logarithmic growth phase (1.24 pg/cell on day 4). EPA was initially concentrated in the glycolipid fraction, but this fraction decreased during logarithmic growth, coinciding with the increase in neutral lipid. Docosahexaenoic acid (22:6n‐3, DHA) (0.91 pg/cell) was reported as a major fatty acid (>10 mg/100 g) in all lipid classes on day 1. DHA was depleted quickly from the neutral lipid and glycolipid classes, but at a slower rate from the polar lipid fraction. This work confirms that C. calcitrans is a good source of lipid, in particular EPA, for larval and adult filter feeders in aquaculture.     

Influence of microalga lipid composition on the sexual maturation of Mytilus galloprovincialis: a hatchery study

The effect of microalga lipid composition on the reproduction of the mussel Mytilus galloprovincialis has been assessed to determine the best feeding strategy for producing large quantities of mussel seed. Three diets based on two microalgae Isochrysis galbana (clon T‐iso) and Chaetoceros gracilis were tested. Besides, hatchery groups were compared with mussels from natural populations. Lipid content and fatty acid profile of digestive gland and mantle of both sexes, eggs and microalgae were analysed and related to sexual maturation. Hatchery groups, specifically the one fed on T‐iso, showed better results in reproduction success, and these differences were reflected on tissue and egg lipid composition. Microalga fatty acid profile influenced tissues and sexes, and higher levels of 18:1n‐9, 22:6n‐3 (DHA) and 18:2n‐6 were detected in groups fed on T‐iso while higher level of 20:5n‐3 (EPA) and 16:1n‐7 in groups fed on C. gracilis. Evidence of synthesis capacity of EPA from 18:4n‐3 and DHA from EPA is detected comparing their levels and the mobilization between tissues. Egg fatty acid profile was influenced by the female diet, and differences among groups were detected and confirmed by PCAs.     

Growth and kinetics of lipids and fatty acids of the clam Venerupis pullastra during larval development and postlarvae

This study examines the larval development, metamorphosis and postlarval stage of Venerupis pullastra in relation to growth, lipids content and fatty acid composition, specifically those believed to be essential for most bivalves (i.e. 20:5n‐3 and 22:6n‐3). Clam larvae were fed with two species of microalgae supplied individually or mixed –Isochrysis galbana and Tetraselmis suecica–species normally used in bivalve hatcheries. Larvae fed with T. suecica showed a progressive accumulation of lipids and fatty acids but did not survive to metamorphosis. Contrarily, larvae fed with I. galbana or mixed diet showed a progressive decline in lipids and essential fatty acids (20:5n‐3 and 22:6n‐3) from the pediveliger stage onwards, and a survival rate of 95% until the start of metamorphosis. The lower content in n‐6 and the absence of 22:6n‐3 in T. suecica diet might contribute to the massive mortality observed for larvae fed with this diet. That diet seems to fail in the supply of some particular nutrient that allows energetic transformation of reserves for growth and metamorphosis. Nevertheless, larvae fed on mixture diet showed higher weight growth values at postlarval stage than those larvae fed on I. galbana diet.     

Comparative growth and survival of spat of the Caribbean pearl oyster,Pinctada imbricata cultivated indoor with microalgae diets and outdoor with natural diet

We report the results of survival and growth in size and dry mass of spat of the Caribbean pearl oyster Pinctada imbricata cultivated under outdoor (field culture) and indoor (Laboratory) conditions. Field group fed on environmental seston. Laboratory groups were fed with mono, binary and ternary mixtures of three cultivated algae: Isochrysis galbana (Ig), Tetraselmis chuii (Ig) and the Chaetoceros sp. (Ch‐A, isolated from north‐eastern Venezuela). After 30 days of trial, fatty acid profiles of spat were determined along with growth in length and height shell, adductor muscle and soft tissue dry mass. During the field grow‐out phase (field culture), samplings were performed at days 1, 15 and 30 to measure environmental variables of phytoplankton biomass (chlorophyll a), dissolved oxygen, seston, temperature and salinity. A significant increase in size and soft tissue mass occurred in spat fed the diets including the tropical diatom (Chaetoceros sp.). In contrast, monoalgal diets of Tc and Ig yielded no significant differences in size and mass of spat, compared with the field culture. These results suggest that nutritional requirements of cultivated spat for specific fatty acids of physiological importance for marine bivalves, such as: 16:0, 16:1n‐7, 18:2n‐6, 20:4n‐6, 18:3n‐3 and 20:5n‐3, were satisfied from microalgal diets with Ch‐A, alone or in combination, compared with spat fed from the field culture.     

Biomass production,proximate composition and fatty acid profile of the local marine thraustochytrid isolate,Schizochytrium sp. LEY7 using low‐cost substrates at optimum culture conditions

This study was conducted to investigate low‐cost substrate alternative and the optimum culture conditions in mass producing the local marine thraustochytrid, Schizochytrium sp. LEY7 isolated from the mangrove leaves of Baybay, Southern Leyte Philippines. Results showed that Schizochytrium sp. LEY7 is able to utilize commercial grade glucose and yeast extract from NaCl‐treated baker's yeast as source of carbon and micronutrients respectively. Cost of mass producing the thraustochytrid isolate using the alternative production substrates was substantially reduced. Incubation temperature and salinity levels were the two growth factors significantly affecting the biomass production of the isolate. The short duration of lag phase shown by the isolate suggests a growth advantage in that cells are readily able to adapt to their new environment. Total lipids averaged to 19.4%. Principal fatty acids were palmitic acid (C16:0) with 33.52% and docosahexanoic acid (DHA, C22:6n‐3) with 39.92% proportion to total fatty acid. Eicosapentaenoic (C20:5n‐3, 1.01%) and arachidonic (C20:4n‐3, 0.90%) are present but in relatively lower amount. Our findings showed the potential of low‐cost substrate in mass producing the local thraustochytrid isolate, Schizochytrium sp. LEY7 as lipid and polyunsaturated fatty acid source in aquaculture. Biomass production was enhanced by optimizing the culture conditions.     

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.     

Cell growth, effect of filtrate and nutritive value of the tropical Prasinophyte Tetraselmis tetrathele (Butcher) at different phases of culture

A local algal isolate Tetraselmis tetrathele was studied to determine the suitable levels of three growth factors (nutrient medium, light intensity and photoperiod) for mass culture. Significantly higher population cell count (141.92 × 10⁴) were found in 4‐day‐old cultures (exponential phase) enriched with Conwy medium and exposed continuously to 93.31–103.5 μmole photon m^?2 s^?1 light intensity compared with two other media (F, SEAFDEC/AQD) under the same light conditions. Cultures exposed to higher levels of photosynthetic photon flux density and continuous photoperiod had a significantly higher cell count regardless of nutrient media used. The chemical composition of T. tetrathele varied as the culture aged. Significantly higher crude protein (49.6%) and crude ash (15.9%) were found in cultures harvested at exponential than at stationary phase of growth. In contrast, significantly higher carbohydrate (55.2%) was noted as the culture aged. There was an increase in the percentage of saturated, monoenoic and n‐3 highly unsaturated fatty acids at the stationary phase of growth. Addition of filtrate from various phases of growth and from 10‐day‐old cultures at various concentrations stimulated cell growth of T. tetrathele. This study identified the optimum growth conditions for mass culture of T. tetrathele and demonstrated its change in the chemical composition as the culture aged.     

Effect of different plant oils on growth performance,fatty acid composition and flesh quality of rainbow trout (Oncorhynchus mykiss)

This experiment intended to assess the effect of sesame (SO), sunflower (SFO) and linseed (LO) oils on growth performance, fatty acid composition of fillet and liver or flesh quality traits of rainbow trout. Fish fed different four iso‐nitrogenous and iso‐lipidic experimental feeds. The control feed contained only fish oil as the primary lipid source. The fillet eicosapentaenoic acid and docosahexaenoic acid levels were the highest in fish fed control feed. In contrast, the liver eicosapentaenoic acid level was the highest in fish fed LO feed. Fish fed SFO feed had the highest level of total n?6 fatty acids in fillet and liver. Fish fed SO feed had the highest level of 18:1 n?9 fatty acid in fillet and liver. During the 12 days refrigerated storage period at 1°C, thiobarbituric acid (TBA) and pH values gradually increased in all dietary groups. However, trimethylamin nitrogen (TMA‐N) values increased in all dietary groups between days 0 and 9 during the storage period. Generally, pH value in fillets of control group was slightly higher than the other fish groups during 12 days refrigerated storage. Nevertheless, the chemical indicators of spoilage, TBA, TMA‐N and pH values were in the limit of acceptability for human consumption. Results of growth performance and chemical tests in the present study showed that sesame, linseed and sunflower oils could be used in feeds for rainbow trout. Moreover, we concluded that further researches should be carried out on the partial replacement of fish oil by sesame oil in rainbow trout nutrition.     

Effects of starvation and feeding on the fatty acid profiles of Stage I phyllosoma of the spiny lobster, Jasus edwardsii

Fatty acid analyses were conducted on newly hatched and 8‐day‐old‐starved and fed Stage I phyllosoma larvae of the spiny lobster, Jasus edwardsii. Fed animals were offered excess 1.5 mm juvenile Artemia (enriched using the alga Isochrysis galbana, Tahitian isolate, T. iso.). After 8 days, there were significant increases in larval dry weight and the proportion of lipid in fed phyllosoma, whereas these parameters decreased in starved phyllosoma. The abundance of the saturated fatty acids 16 : 0 and 18 : 0 increased in both starved and fed phyllosoma, whereas the main monounsaturated fatty acids 16 : 1n‐7, 18 : 1n‐9 and 18 : 1n‐7 increased with feeding but decreased with starvation. There were no significant differences in the relative proportions of the highly unsaturated fatty acids (HUFAs) arachidonic (AA, 20 : 4n‐6), eicosapentaenoic (EPA, 20 : 5n‐3) and docosahexanoic (DHA, 22 : 6n‐3) acids between newly hatched and starved animals, whereas quantitatively DHA decreased with starvation and feeding. The DHA/EPA ratio was significantly lower in the starved and fed phyllosoma (0.5) compared with that found in the newly hatched phyllosoma (0.9). The lipid profiles of the newly hatched, starved and fed phyllosoma contained large amounts of n‐6 fatty acids resulting in low n‐3 : n‐6 ratios (2.8, 2.7 and 1.6 respectively). The importance of these results and the ability of enriched Artemia to provide a suitable fatty acid profile for this species are discussed.     

Marine microalgae as dietary supplements in the culture of juvenile Chinese horseshoe crabs,Tachypleus tridentatus (Xiphosura)

Five treatments (short‐neck clam Ruditapes philippinarum and four formulated diets with the green microalgae Dunaliella tertiolecta or the golden‐brown microalgae Isochrysis galbana in the ratio (dw/dw) of 5% or 10% to that of clam meat) were used to investigate the growth performance and haemolymph quality of juvenile Chinese horseshoe crabs Tachypleus tridentatus under laboratory culture. At the end of the 12‐week study, various growth and moulting indicators as well as haemolymph biochemical parameters did not show any significant differences among the treatments. Significantly higher percentages of haemolymph amoebocyte viability and granular‐spherical amoebocyte state were noted in both 5% and 10% I. galbana‐supplemented diets compared to that of clam meat. However, the percentages of these two haemolymph parameters in juveniles fed with D. tertiolecta decreased significantly at the end of the experiment. Such differences were attributed to the presence of polyunsaturated fatty acid (PUFA), notably eicosapentaenoic acid (EPA), in I. galbana that was absent in D. tertiolecta and clam meat. Like many marine invertebrates, juvenile horseshoe crabs do not naturally obtain sufficient PUFAs from their diets to meet developmental and physiological needs; hence, supplementing microalgae with high levels of EPA in a protein‐rich diet boosts immune competence and the health status of juvenile horseshoe crabs while under culture.     

Effect of live algae used as green water on survival,growth, behaviour,ontogeny and bacterial profile of lobster larvae (Homarus americanus Milne Edwards)

Green water is a technique commonly used in aquaculture, that consists of adding live algae in the water culture and its benefits have been shown for several species. Several hypotheses exist to explain the benefits of green water: increase in nutritional value; action as a probiotic; increase in contrast to reveal preys for larvae; or increase in predator behaviour of larvae. Green water produced with a mix of strains Isochrysis galbana and Chaetoceros muelleri (50:50, cells:cells) applied in four different ways was tested. The survival and the growth of American lobster (Homarus americanus) between stage I and stage IV post‐larvae were not affected by the addition of live algae. The lipid classes were not affected by the addition of algae and limited variation was observed in the fatty acids and bacterial profiles. Furthermore, the green water techniques had a limited effect on the behaviour of post‐larvae stage IV lobster at releasing. Behaviour was mostly affected by the age of post‐larvae. The bacteria Lewinella sp., Leucothrix sp. and Thiothrix sp. appeared to represent a common and core component of Stage IV lobster post‐larvae microflora. The results show that the algae do not increase either nutritional value or feed intake of the lobster larvae. Probiotic effect may be more important when larvae are raised in a close system where potential bacterial pathogens could have more chances to colonize the culture. Also, the dark green colour of the larval tank used in this study may have mimicked the effect of green water in the control group. Biochemical results suggest that dietary supplementation with phospholipids and DHA is needed in a lobster hatchery using frozen Artemia and our open formula Dry mix.     

Assessment of the fecundity,population growth and fatty acid composition of Apocyclops royi (Cyclopoida,Copepoda) fed on different microalgal diets

The brackish cyclopoid copepod Apocyclops royi is used in Taiwanese aquaculture industry as a prey for fish larvae. This study investigated the effects of seven microalgal diets, namely single‐species diets of Isochrysis galbana (ISO), Nannochloropsis oculata (NAN), and Tetraselmis chui (TET), two‐species diets (ISO+NAN, ISO+TET and TET+NAN), and a three‐species diet (ISO+NAN+TET), on the population growth, female fecundity and fatty acid composition of A. royi. For reproductive traits, the combination ISO+NAN was found to be the most supportive diet for both population growth and female fecundity. For nutritional value, copepods fed ISO and ISO+NAN were detected to have the highest content of docosahexaenoic acid (DHA) (18.99% and 10.73% total fatty acid, respectively) and, more importantly, a high DHA/EPA ratio (6.09 and 4.09, respectively). Additionally, a comparison of fatty acid composition between copepods and microalgae gives a tentative indication that A. royi may have the ability to synthesize long‐chain polyunsaturated fatty acids (PUFA) from short‐chain PUFA. Our findings illustrate that ISO+NAN is the most suitable microalgal diet for mass culturing A. royi because it increases productivity and enhances the nutritional value of the copepods for use as fish larvae prey.     

Evaluation of nutritional and environmental variables during early larval culture of pigfish Orthopristis chrysoptera (Linnaeus)

Pigfish (Orthopristis chrysoptera Linnaeus) are a commonly used baitfish in the southeastern United States. Aquaculture methods for broodfish spawning and juvenile grow‐out have been developed but there is still a paucity of information regarding larval culture methods. Five, short duration (10 days) experiments were conducted to determine effective strategies to yield high larval survival and growth during early development. Experiment one examined the rotifer enrichments Ori‐Green, DHA Protein Selco, and AlgaMac 3050 as well as a non‐enriched control along with corresponding fatty acid levels in the enriched rotifers and pigfish larvae. Experiment two evaluated three, once daily feeding frequencies of either 5, 10 or 20 rotifers mL^?1. Experiment three compared feeding 20 rotifers mL^?1 once daily to feeding 5 rotifers mL^?1 twice daily. Experiment four examined four different larval stocking densities: 50, 75, 100, or 125 larvae L^?1. Experiment five examined green water strategies using either live Tahitian strain Isochrysis galbana (Parke) or Nannochloropsis oculata (Hibberd) paste at either 250 000 or 500 000 cells mL^?1 as well as a clear water control. Results indicated rotifer enrichment with DHA Protein Selco and green water application using live T‐ISO at 500 000 cells mL^?1 had the highest survival of pigfish during early stages of larval culture. A once daily rotifer feeding regime of 20 rotifers mL^?1 and stocking density of 50 larvae L^?1 also improved survival. These results provide producers with methods to improve efficiency for pigfish larval culture and provide researchers with new foundational data, such as potential fatty acid requirements.     

The effect of food quality on glycogen content,the fatty acid profile and winter mortality in cultivated oyster spat (Ostrea edulis)

Winter mortality in hatchery reared oyster spat (Ostrea edulis) that received three different diets during the summer period was investigated. Oysters fed a natural type diet had a winter mortality of 18.3 ± 6.3% while oysters fed cultivated algae (a mixture of Tetraselmis suecica, Isochrysis galbana and Chaetoceros muelleri) had a mortality of 73.0 ± 9.7%. A group of oysters fed a mix between the two diets had a mortality of 54.7 ± 10.6%. Tissue samples were taken at the start of the experiment, after the summer period and after the winter period in order to determine growth and the content of glycogen and fatty acids. The glycogen content decreased for all groups during the winter but the decrease was highest in oysters fed the natural diet. This group also contained the largest variety of fatty acids, but there was no difference in the content of the essential fatty acids EPA, DPA and DHA between the groups. It is concluded that transplantation of spat to the sea in spring and early summer may reduce winter mortality since the feeding period on a more varied natural algal diet is prolonged compared to transplantation of spat later in the season.     

The effect of seaweed extracts,as a supplement or alternative culture medium,on the growth rate and biochemical composition of the microalga,Isochrysis galbana (Park 1949)

Aqueous extracts of green [Ulva lactuca Linnaeus and Enteromorpha intestinalis (Linnaeus) Nees] and red [Gracilaria corticata (J. Agardh) J. Agardh] seaweeds from the Persian Gulf of Iran were examined for their potential usefulness as components of microalga Isochrysis galbana culture medium against conventional f/2 medium. Isochrysis galbana was successfully cultured using the tested seaweed extracts (SWE) and exhibited higher or similar cell density and biomass when SWE were used as a supplement or an alternative medium respectively. When the SWE were used as an alternative medium, microalgal protein, lipid and ash content were similar but carbohydrate increased compared with control. Total saturated fatty acids decreased with a corresponding increase in total mono‐ and polyunsaturated fatty acids following supplementation of f/2 medium with SWE. Eicosapentaenoic acid (EPA) was not affected by SWE treatments but docosahexaenoic acid (DHA) tended to decrease, except for I. galbana cultured with U. lactuca extract. With the exception of potassium, SWE did not significantly impact the mineral content of cultured I. galbana. The study points to the potential usefulness of specific SWE in the production of microalgae as a food source in aquaculture.     

Effects of culture conditions on larval growth and survival of stalked barnacles (Pollicipes pollicipes)

Pollicipes pollicipes (Crustacea: Scalpelliformes) is a highly prized food in Portugal and Spain and consequently a species of considerable interest to aquaculture. Surprisingly, however, larval culture conditions for this barnacle have not been optimized. This study investigated the effects of temperature, diet, photoperiod and salinity on the growth and survival of P. pollicipes larvae. Temperature had a significant effect on specific growth rate (2.6–5.9% total width per day, from 11 to 24°C), reducing mean development time to the cyprid from 25 days at 11 °C to 10 days at 24°C, although this was accompanied by a significant increase in mortality to over 90% above 22°C. Mid‐range temperatures (15–20°C) maximized total survival (19–31% respectively). Algal diets of Tetraselmis suecica, T. suecica/Skeletonema marinoi and S. marinoi/Isochrysis galbana did not affect specific growth rate significantly, but survival (on average 39% in 15 days) and the proportion of high‐quality healthy cyprids was significantly higher on the latter two diets (11–15% of initial number of larvae). Photoperiod did not significantly affect the survival, although specific growth rate was significantly higher at 24:0 and 16:8 L:D. Salinity (20–40 g L^?1 range) did not affect growth and survival significantly. The best growth and survival were accomplished using rearing temperatures of 15–20°C, daily feeding with T. suecica/S. marinoi or I. galbana/S. marinoi and a photoperiod of 24:0 L:D.     

Dietary lipid sources for seabream and seabass: growth performance, tissue composition and flesh quality

Due to its traditionally good availability, digestibility and high content of n ? 3 HUFA, fish oil is the main lipid source in fish feeds. However, world demand for this product has grown significantly in recent years, whereas its production, based on fisheries landings, is static. The purpose of the present study was to assess the effect of partial replacement of fish oil in compound diets for gilthead seabream and seabass, by several vegetable oil sources, on growth, dietary fatty acid utilization and flesh quality. Five iso‐energetic and isoproteic experimental diets were formulated (25% lipid content). Fish oil was the only added lipid source in the control (FO) diet, and it was included in the other experimental diets at a level high enough (40% of FO diet) to keep the n ? 3 HUFA levels well over 3% in order to cover the essential fatty acid requirements of these species. Fish oil was replaced by soyabean oil (SO), rapeseed oil (RO) and linseed oil (LO) or a mixture (Mix) of them. Feed intake in all dietary groups was in the range of results obtained for commercial diets in both species, and growth and feed utilization were very good. The results show that, providing a minimum content of essential fatty acids in the diet, it is possible to replace up to 60% of the fish oil by SO, LO and RO or a mixture of them in diets for seabream and seabass, without compromising fish growth. Fatty acid composition of liver and muscle reflected that of the diet, but utilization of dietary lipids differed between these two tissues and was also different for the different fatty acids. Despite reduction in dietary saturated fatty acids by the inclusion of vegetable oils, their levels in fish liver were as high as in fish fed the fish oil diet, whereas, in muscle, levels were reduced according to that in the diet. Linoleic and linolenic acids were accumulated in the liver proportionally to their levels in the diet, suggesting a lower oxidation of these fatty acids in comparison to other 18C fatty acids. Regarding eicosapentaenoic acid (20 : 5n ? 3; EPA), docosahexaenoic acid (22 : 6n ? 3; DHA) and arachidonic acid (20 : 4n ? 6; ARA), these essential fatty acids were reduced in the liver at a similar rate, whereas DHA was preferentially retained in the muscle in comparison with the other fatty acids, denoting a higher oxidation particularly of EPA, in the muscle. Some other PUFA increased despite their low dietary levels in seabream fed LO diets and in seabass fed SO diet, suggesting the stimulation of delta‐6 and delta‐5 desaturase activity in marine fish. Despite differences in fatty acid composition, fillet of fish fed vegetable oils was very well accepted by trained judges when assessed cooked.     

Effect of algal addition on stability of fatty acids and some water‐soluble vitamins in juvenile Artemia franciscana

A minor stabilization effect was found for the content of total lipids, total fatty acids and docosahexaenoic acid (DHA) when Artemia franciscana was maintained at high concentrations of Isochrysis galbana for 72 h at 12 °C, both in 3‐ and 4‐day‐old individuals. The eicosapentaenoic (EPA) level was only stabilized at higher algal concentrations in the 4‐day‐old A. franciscana. In the 3‐day‐old A. franciscana, the EPA content increased at all algal concentrations during the first 24 h of post enrichment, presumably as an effect of DHA catabolism. Apparently, the 4‐day‐old A. franciscana metabolized DHA, and other lipids, faster than the 3‐day‐old A. franciscana did. During the 72 h incubation with I. galbana, the content of ascorbic acid (AA) in A. franciscana increased approximately to 1000–1200 μg g^–1 dry weight (DW) at algal concentrations above 3 mg C L^–1, close to AA content of the algae. The vitamin B₆ content in A. franciscana decreased from approximately 20 to 4–11 μg g^–1 DW, with highest loss rates at the higher algal concentrations. The thiamin content of A. franciscana was independent of algal concentration and remained at 20–30 μg g^–1 DW. The nutritional effects of the algal incubation on the 3‐ and 4‐day‐old A. franciscana at algal concentrations which can be used during the cultivation of Atlantic‐halibut larvae (<2 mg C L^–1) was insignificant, except for the small enrichment effect of AA already at 1 mg C L^–1. Other beneficial effects of the algae should not be ruled out, like possible effects on the microflora of A. franciscana even at algal concentrations less than 2 mg C L^–1.     

Effect of three diets on the gametogenic development and fatty acid profile of Paracentrotus lividus (Lamarck, 1816) gonads

In this study, the effects of three diets were investigated to enhance Paracentrotus lividus production for commercial purposes. P. lividus were fed ad libitum for 80 days with: diet A—fresh Codium tomentosum Stackhouse, 1797; diet B—formulated using a jellified mix of macroalgae and vegetables, including C. tomentosum (20%), Coralina sp. Linnaeus, 1758 (17%), cabbage Brassica oleracea var. capitata Linnaeus, 1753 (30%), carrot Daucus carota Linnaeus, 1753 (30%) and agar (3%) as a gelling agent. Diet C consisted of maize Zea mays Linnaeus, 1753 (56%) and New Zealand spinach Tetragonia tetragonoides (Pallas, 1781) Kuntze, 1891 (44%). Their effects on the gonadal and somatic growths, gonadosomatic index (GI) and gametogenesis were evaluated, as well as on the total lipid content and fatty acid composition of sea urchin's gonads. Diet A provided high values of eicosapentaenoic acid (EPA). Gonads of sea urchins fed with diet A were found mostly in growth and maturation stages of gametogenesis and showed the lowest lipid content. Sea urchins fed with diet B presented their gonads in the reabsorption stage and had the highest values of omega‐3 polyunsaturated fatty acids (PUFAs). Sea urchins fed with diet C were in the early stages of gametogenesis and had the highest values of lipid content, plus omega‐6 PUFAs. Once as an ingredient in a balanced mix with vegetables, C. tomentosum can be a key factor to the development of new promising high‐quality and low‐cost feed for P. lividus roe enhancement.