Microalgal Diets Research Articles

A novel stepwise salinity acclimation method to improve the survival of freshwater microalgae Haematococcus lacustris in seawater salinity.

Freshwater microalga Haematococcus lacustris rich in astaxanthin, as a supplemental live diet can directly supply natural astaxanthin to the aquaculture organisms, except marine aquaculture organisms, since H. lacustris cannot tolerate seawater salinity. The objective of the present study is to provide a salinity acclimation method that allows H. lacustris to survive and accumulate astaxanthin with the aim of developing a novel supplemental live diet for marine aquaculture organisms. H. lacustris cultured in freshwater was subjected to different stepwise salinity acclimation processes (two-, three-, and four-shift). As the controls, H. lacustris was exposed to five constant salinities conditions (0, 0.05, 0.075, 0.3, and 0.6M NaCl, respectively). Among the controls, almost all cells in the 0.3M and 0.6M NaCl conditions died immediately. In contrast, H. lacustris in the stepwise salinity acclimation processes survived in 0.6M NaCl (equivalent to seawater salinity of 35 psu), showing the highest living-cell proportion (50.0%) and astaxanthin yield (0.72mg·L-1) in the four-shift. The present study first demonstrated that H. lacustris tolerated seawater salinity through a stepwise acclimation process, proving a new strategy to supply live microalgal diets rich in natural astaxanthin for marine aquaculture.

The uptake of dissolved glucose by juvenile green‐lipped mussels (Perna canaliculus)

AbstractA major expense in the operation of bivalve nurseries is the culture of high‐quality live microalgae feeds, and efforts to develop effective alternative feeds have had limited success. Juvenile bivalves are known to be able to absorb dissolved nutrients, but this ability has received minimal attention as a route for supplementary feeding. This study assessed the capacity of juvenile green‐lipped mussels (GLMs) (Perna canaliculus) to uptake and assimilate dissolved glucose at five experimental concentrations (i.e. 10 µg mL−1, 100 µg mL−1, 1 mg mL−1, 10 mg mL−1 and 30 mg mL−1) as a supplement to cultured microalgae. Growth and survival of the mussels were measured over 3 weeks. Although all glucose concentrations improved the performance of mussel spat compared to the control, the best performing was a concentration of 1 mg mL−1 of dissolved glucose which enhanced daily spat growth 2.7 times that of the control live microalgal diet without glucose. Survival was high (i.e. >95%) for all treatments except for the highest experimental concentration of glucose, for which a concentration of 30 mg mL−1 resulted in mean mortality of 24%. Mussel spat supplemented with dissolved glucose accumulated up to 30% greater lipid and improved the carbohydrate content per mg g−1 of ash‐free dry weight as much as 3.5 times compared to those in the control treatment, indicating that they were in greater nutritional condition. This demonstration that dissolved glucose can be used to fuel growth by GLM spat at concentrations as low as 10 µg mL−1 suggests that other soluble nutrients may also act as a supplemental feed for cultured juvenile molluscs. Dissolved nutrients have the potential to improve the performance of spat in nursery systems while simultaneously reducing the reliance of cultured microalgae as a sole feed input.

First success in captive breeding of the Tiger Cowrie, Cypraea tigris (Gastropoda: Cypraeidae), with notes on its early life development

ABSTRACT The larval development of cowries has remained underexplored due to challenges associated with restricted growth and high mortalities, and as a result, their larvae never achieve competency or metamorphosis. In this study, we conducted a series of experiments using Cypraea tigris larvae to optimise the culture protocols. Broadly, there were no apparent differences in larval survival rates among the seawater quality levels (0.2, 1 aged, 50 μm filtered seawater). In contrast, a microalgal diet solely of Tisochrysis lutea and a mixed diet of Rhodomonas salina + Chaetoceros mulleri had higher larval survival rates than two other mixed diets (i.e., T. lutea + Tetraselmis suecica and T. suecica + R. salina). The provision of 10 ppm of the antibiotic streptomycin sulphate also boosted larval survival by preventing ciliate infection and minimising bacterial growth. We subsequently improved culture protocols by applying new information from these experiments and report the first successful captive breeding of C. tigris through to settlement. The C. tigris larvae reared at 28°C attained competency as early as 40 days post-hatching and metamorphosed by 42 days upon transfer to a well-conditioned tank. Observations of C. tigris larvae and early-stage juvenile development were documented for the first time and are reported herein.

Large-scale culturing of the subpolar foraminifera Globigerina bulloides reveals tolerance to a large range of environmental parameters associated to different life-strategies and an extended lifespan.

The subtropical to subpolar planktic foraminifera Globigerina bulloides is a calcifying marine protist, and one of the dominant foraminiferal species of the Nordic Seas. Previously, the relative abundance and shell geochemistry of fossil G. bulloides have been studied for palaeoceanographic reconstructions. There is however a lack of biological observations on the species and a poor understanding of its ecological tolerances, especially for high latitude genotypes. Here, we present observations from the first extensive culturing of G. bulloides under subpolar conditions, including the first low temperature (6-13°C) and variable salinity (30-38) experiments. Carbonate chemistry (pH and [CO3 2-]) was also manipulated. Experimental conditions were chosen to reflect a range of plausible past and future scenarios for the Nordic Seas. We found G. bulloides to be tolerant of environmental conditions well outside their optimal range (<10°C, salinity <33, pH <8). Observed life span was up to three months, which was attributed to a microalgal diet. Two alternative life strategies were employed, whereby individuals either experienced rapid growth and death, or a prolonged lifespan with minimal growth and death via slow decay. We posit this could help explain differences in geochemical signals recorded from different size fractions of fossil specimens used for palaeoceanographic reconstructions.

Effects of Three Microalgal Diets Varying in LC-PUFA Composition on Growth, Fad, and Elovl Expressions, and Fatty Acid Profiles in Juvenile Razor Clam Sinonovacula constricta

The razor clam Sinonovacula constricta is the first marine mollusk demonstrated to possess the complete long-chain polyunsaturated fatty acids (LC-PUFA) biosynthetic pathway. This study explored the impact of different microalgae on growth, Fad and Elovl expressions, and fatty acid (FA) profiles in juvenile S. constricta. Results revealed that juveniles fed with Isochrysis galbana (rich in DHA) or Chaetoceros calcitrans (rich in EPA) consistently exhibited higher growth than those fed Chlorella sp. (rich in LA and ALA), underscoring the importance of dietary LC-PUFA in S. constricta’s development. Expression of most Fad and Elovl in C. calcitrans and I. galbana-fed juveniles were initially up-regulated, then down-regulated, suggesting LC-PUFA demand for faster growth. Although Chlorella sp.-fed juveniles exhibited decreased mRNA levels for most genes, levels were notably higher lately compared to those fed C. calcitrans or I. galbana, hinting at potential LC-PUFA biosynthesis induction. FA profiles in S. constricta generally mirrored those in ingested microalgae, implying direct FA accumulation from diets. Some microalgal FA were absent in farmed S. constricta, while others emerged, indicating S. constricta’s ability to selectively accumulate and synthesize FA. This study enhances the understanding of dietary FA metabolism in S. constricta, valuable for selecting appropriate microalgae in its farming practices.

Synthesis and Structural Characterization of Selenium Nanoparticles-Bacillus sp. MKUST-01 Exopolysaccharide (SeNPs-EPS) Conjugate for Biomedical Applications.

Exopolysaccharides (EPS) are exogenous microbial metabolites generated predominantly during the development of bacteria. They have several biological potentials, including antibacterial, antioxidant, and anticancer actions. Polysaccharide-coated nanoparticles have high biological activity and are used in treatments and diagnostics. In this research, selenium nanoparticles (SeNPs) are synthesized and conjugated with bacterial (Bacillus sp. MKUST-01) exopolysaccharide (EPS). Initially, the creation of SeNPs conjugates was verified through UV-Vis spectral examination, which exhibited a prominent peak at 264 nm. Additionally, X-ray diffraction (XRD) analysis further substantiated the existence of crystalline Se, as evidenced by a robust reflection at 29.78°. Another reflection observed at 23.76° indicated the presence of carbon originating from the EPS. Fourier transform infrared spectroscopy (FT-IR) analysis of the EPS capped with SeNPs displayed characteristic peaks at 3425 cm-1, 2926 cm-1, 1639 cm-1, and 1411 cm-1, corresponding to the presence of O-H, C-H, C=O, and COO-groups. The SeNPs themselves were found to possess elongated rod-shaped structures with lengths ranging from 250 to 550 nm and a diameter of less than 70 nm, as confirmed using scanning electron microscopy and particle size analysis. In contrast to the SeNPs, the SeNPs-EPS conjugates showed no hemolytic activity. The overall antioxidant activity of SeNPs-EPS conjugates outperformed 20% higher than SeNPs and EPS. Additionally, experimental observations involving gnotobiotic Artemia nauplii experiments were also recorded, such as the supplementation of EPS and SeNPs-EPS conjugates corresponding to enhanced growth and increased survival rates compared to Artemia nauplii fed with SeNPs and a microalgal diet.

Effects of temperature and microalgal diet on the fecundity, population growth and fatty acid composition of Pseudodiaptomus ishigakiensis (Calanoid, Copepoda)

This study aims to investigate the optimal culture conditions of the marine calanoid copepod Pseudodiaptomus ishigakiensis, which is considered emerging live feed for marine larviculture. The effects of temperatures (20 °C, 25 °C, 30 °C and 35 °C) and microalgal diets Isochrysis galbana (ISO), Proteomonas sulcata (PRO), Chlorella sp. (CHL) and Tetraselmis chuii (TET) on the fecundity, population growth rate, composition of developmental stages and fatty acid composition of P. ishigakiensis were evaluated. The highest population growth rate (60.6 ± 4.9 ind./day) was found at 30 °C with the significantly-highest number of naupliar individuals (726.7 ± 30.6 ind.) and a high level of fecundity (14.4 ± 0.7 eggs/female). Whereas the lowest population growth was found at 35 °C (0.4 ± 0.2 ind./day). In the diet experiment, the population growth rate (73.8 ± 1.9 ind./day) was the highest in the PRO treatment with a great number of naupliar individuals (912.50 ± 24.7 ind.) and fecundity (13.4 ± 0.6 eggs/female). Both TET and CHL treatments showed the lowest population growth (0.5 ± 0.1 ind./day and 0.2 ± 0.1 ind./day, respectively) and absence of ovigerous female at the end of experiment, which indicated their unsuitability as feeds for P. ishigakiensis. Fatty acid compositions of copepods were affected by the fatty acid content of their microalgal diets. The copepods fed on ISO and PRO contained higher levels of eicosapentaenoic acid (EPA, C20:5 n-3; 4.51 ± 1.29–5.42 ± 0.64%) and docosahexaenoic acid (DHA, C22:6 n-3; 4.00 ± 0.34–5.92 ± 1.28%) composition compared to CHL and TET (EPA: 0.48 ± 0.15–2.65 ± 1.27%; DHA: 1.68 ± 0.26–1.89 ± 0.14%). This study revealed the optimal culture conditions and nutritional value of the copepod P. ishigakiensis, which provides implications for the managements of their mass culture, and utilization in marine larviculture.

Potential Effects of Microalgae-Supplemented Diets on the Growth, Blood Parameters, and the Activity of the Intestinal Microbiota in Sparus aurata and Mugil cephalus

This work aimed to assess the suitability of a microalgal blend as a dietary ingredient for feeding juveniles of marine carnivorous and herbivorous teleost, as is the case of Sparus aurata and Mugil cephalus, respectively, and to isolate microorganisms from different media and characterize them on the base of their enzymatic activities and their antagonism against important fish pathogens. Thirty juveniles of each species (70 ± 3.2 g S. aurata mean weight and 47 ± 2.8 g M. cephalus mean weight) were distributed in four tanks (15 individuals each) corresponding to four independent dietary treatments (control and microalgae diets designed for each species). Fish were fed their corresponding diets ad libitum for 108 days. At the end of the trial, fish were weighed, and plasma, liver, perivisceral fat, and the entire intestines were obtained for the evaluation of growth performance and metabolic assessment. Furthermore, 117 bacterial strains were isolated in different culture media from the gastrointestinal tract of S. aurata fed the microalgae blend and further characterized for their potential use as probiotics in aquaculture. S. aurata fed the microalgae-supplemented diet (25% dietary inclusion) showed a significant increase in weight gain, specific growth rate, feed efficiency, hepatosomatic, and intestine length indices. However, growth performance and somatic indices in M. cephalus were not affected by the experimental diets. Plasma samples from S. aurata fed the microalgal diet revealed higher levels of glucose and triglycerides and a decrease in cortisol levels. No significant differences were found in any biochemical parameters among the experimental diets in M. cephalus. In conclusion, both species demonstrated a favorable adaptation to the nutritional formulation employed in this study, and bacterial strains UMA-169 and UMA-216 (both identified as Bacillus pumilus) could be considered for use in aquaculture as they might benefit host health by improving digestion and absorption of different energy sources and by minimizing the colonization of pathogenic species.

Fatty acid contribution of microalgal diets on spat performance of the tropical mangrove oyster Crassostrea rhizophorae, in Mochima Bay, Venezuela

Fatty acids play a fundamental role in the ecology and growth of many invertebrates, such as filter-feeder bivalve. To guarantee adequate nutrition during transfer from the nursery to the natural environment, we studied the survival, growth and fatty acid (FA) profile of Crassostrea rhizophorae oyster spat fed with seven microalgae combinations of Chaetoceros sp. Araya strain (Ch-A), Tisochrysis lutea (Tl) and Tetraselmis chuii (Tc). The diets included three monoalgal diets (Ch-A, Tl and Tc), three binary combinations (Tl+Ch-A, Tl+Tc and Ch-A+Tc) and one ternary mixture (Tc+Ch-A+Tl). Groups of triplicated carboys each containing 21 oyster spat were used to test the experimental diets, while an additional group was deployed directly in the environment as a control. After 36 days, total lipids, FA profiles and biometric parameters of the spat were analyzed.​ The spat were then transferred to the outdoor environment, and cultivated under suspension conditions for 30 additional days. At the end of this period, FA profiles and growth were again determined. Environmental variables were sampled weekly. Highest shell height growth and soft tissues mass were observed in the spat fed with Ch-A in any combination: the mono-algae Ch-A diet, the binary Ch-A+Tc and Ch-A+Tl diets, a tendency that persisted in the outdoor environment. Our results showed lower shell and soft tissues mass growth, and a drop in the levels of certain FAs of the spat after their transfer to the natural environment, such as 14:0, 16:1n-7, 18:1n-9, 18:4n-3 and 20:5n-3 FA. This effect probably reflected a compensation strategy for the scarce availability of food and higher temperatures observed in the natural environment.

Potential for Concentrated Microalgae as Replacement Diets for Juvenile Green-Lipped Mussels, Perna canaliculus

The nursery culture of bivalves typically relies on the feeding of costly live microalgae, while the use of natural sources of phytoplankton for feed is uncertain due to their variable quality and abundance. Replacement diets have been applied in bivalve nursery culture to replace live microalgae with varying success. This study investigated the potential use of two concentrated microalgal diets at a range of levels of substitution with live microalgae. Shellfish Diet 1800® (called SD) and LPB™ Frozen Shellfish Diet® (called LPB) were fed to juvenile green-lipped mussels (Perna canaliculus) at five levels of substitution for live microalgae (i.e., 0, 25, 50, 75, and 100%) for 27 days. The mortality of mussels fed with 100% LPB replacement was significantly higher than the mortality of mussels fed at the lower levels of replacement, i.e., 0 and 25%. The overall final size of spat tended to decrease with the increasing level replacement of live microalgae. Proximate analysis (i.e., crude ash-free dry weight, crude protein, crude lipid, and carbohydrate) showed that only the proportion of carbohydrate content of spat was influenced by feeding treatments, with the mean total carbohydrate content of mussels tending to decrease with increasing levels of replacement of live microalgae. The results indicate that both concentrated microalgal feeds (SD and LPB) are effective at replacing live microalgae by up to 50% without compromising the survival and nutritional profile (AFDW, protein, lipid, and carbohydrate content) of juvenile green-lipped mussels and are therefore a useful resource for improving the efficiency of production.

Using combinations of microalgae to condition European flat oyster (Ostrea edulis) broodstock and feed the larvae: Effects on reproduction, larval production and development

Hatchery production of European flat oyster (Ostrea edulis) is erratic and is dependent upon broodstock conditioning and larval rearing conditions, including nutrition at both steps. In this study, the combined effects of broodstock and larval diets upon larval growth, survival, competence and metamorphosis and fatty acid and sterol compositions were studied. Four-year-old broodstock were conditioned in 700-L flow-through tanks (50 oysters per tank) at 19 °C and subjected to three dietary conditions in duplicate during 19 weeks. Two mixed diets were supplied continuously at an equivalent of 2 billion cells per day per oyster: Rhodomonas salina + Chaetoceros neogracile (Rs + C) or R. salina + Thalassiosira weissflogii (Rs + Tw), and the third condition was unfed. Samples of microalgae, released larvae (day 0), and larvae at day 9 were collected, and fatty acids (FAs) in neutral (NL) and polar lipids (PL) and sterols were analysed. Larval collection was continuous to estimate numbers of larvae released, which was dependent upon broodstock diet. Oysters fed Rs + C doubled the number of larvae compared to those receiving Rs + Tw - 47.8 compared to 23.1 million larvae, respectively. FAs in NL and PL, as well as sterol composition of released larvae, differed significantly depending upon broodstock diet. Larvae were reared in 5-L cylinders in a flow-through system at 22 °C. Larvae were subsequently fed different single and mixed microalgal diets in triplicate, incorporating Tisochrysis lutea (T), C. neogracile (C), and Diacronema lutheri (D), at a constant concentration of 1500 μm3 μL−1 at the outlet of the rearing tank. Larval growth responded to both broodstock and larval diets; whereas, larval survival, competence, and settlement were influenced by both factors and their interactions. Broodstock receiving Rs + C produced larvae that grew faster (5.6–10.8 μm day−1) than larvae from the other broodstock dietary regimes (4.6–9.6 μm day−1). Larvae from fed broodstock (Rs + C or Rs + Tw) receiving the bi-specific diet T + C exhibited the highest growth rate (9.5–10.8 μm day−1); whereas, those fed the single diet D. lutheri exhibited low growth and competence (4.6–6.1 μm day−1; 4%) on day 9. Fed larvae originating from broodstock fed Rs + C exhibited better survival (92–97%) than those released by broodstock fed Rs + Tw (70–93%). Except for those supplied with T, fed larvae exhibited higher settlement when originating from broodstock receiving Rs + C. On day 9, FA and sterol compositions of larvae reflected the biochemical content of the larval diets. Overall, the best results were observed in larvae fed T + C originating from broodstock fed Rs + C.

Effects of microalgal diet on growth, survival and fatty acid composition of larvae rock oyster Striostrea prismatica (Gray, 1825)

The biochemical nature and composition of fatty acids (FA's) in microalgae influence the nutritional quality and efficiency of this food source in bivalve larviculture. This research analyses the effect FA's content of Chaetoceros gracilis and Tisochrysis lutea on the FA's composition, growth and survival of Striostrea prismatica larvae. We analysed the FA's profiles of the microalgae, and the tissue of the larvae during a S. prismatica larviculture at day 1 (“D” larvae), day 8 (umbonate larvae) and day 22 (pediveliger) post fertilization (PF). Larvae growth and survival were evaluated during two phases: phase I from day 1 to day 8 PF and phase II from day 9 to day 22 PF. In phase I, we recorded a daily growth rate of 4.76 μm.day−1, while in phase II we recorded increases of 13.24 μm.day−1. In phase I, survival was 36.6%, and decreased further to 9.3% at the end of phase II. The sharp decrease in survival and low growth during phase I could possibly be explained by a specific nutritional deficiency of the microalgae diet (absence of FA's 15:0, 20:4n-3, 20:4n-6 and 22:5n- 3), especially if we consider the starting FA's profile of the “D” larvae. The larvae showed a high nutritional requirement for palmitic, stearic and oleic FA's and long-chain PUFA's, especially 20:5n-3 and 22:6n-3. The absence of these FA's in the diet and their presence in the larval profile suggest that S. prismatica could have the ability to synthesize these FA's; however, more research is needed to corroborate this hypothesis.

Evaluation of suitable micro‐algal diets for intensive culture of the calanoid copepod Acartia bilobata

Copepods are alternative live feed in marine fish hatcheries, and the quality and type of micro-algal diets influence their culture productivity. Three algal species of different groups including prymnesiophyte: Isochrysis galbana (Iso), the diatom: Chaetoceros muelleri (Cht) and eustigmatophyte: Nannochloropsis occulata (Nan) were fed to the calanoid copepod Acartia bilobata. Selected algae were offered as mono-algal diets: T1-Iso, T2-Cht and T3-Nan or as mixed algal diets: T4-Nan + Cht, T5-Nan + Iso, T6-Iso + Cht and T7-Iso + Cht + Nan. Reproductive parameters, egg production, hatching success, nauplii and copepodite survival, development and first maturity, were closely monitored. Results illustrated that I. galbana was the most suitable diet for this copepod species, supporting higher average relative egg production (5631.62 ± 133.49 egg L−1 day−1), hatching success (96.32 ± 1.40%) and superior adult survival (44.44 ± 3.20%). Different algal diets influenced the nauplii and copepodite survival rate. Maximum survival to adults (56.67 ± 3.78%) and shortened development time (5.75 ± 0.12 days) and time to first maturity (4.50 ± 0.12 days) were observed when fed with I. galbana. The groups fed with C. muelleri exhibited lower survival (6.67 ± 0.67%) during development into adults, and the group fed with N. occulata alone or with C. muelleri did not survived till the adults. Amongst seven algal diets tested, I. galbana was found ideal for maximizing culture productivity, and hence recommended for intensive culture of A. bilobata.

High dietary protein, n − 3/ n − 6 ratio and β ‐carotene enhances Paracentrotus lividus (Lamarck, 1816) larval development

The nutritional characteristics of microalgae affect the growth, survival and fatty acid composition of sea urchin larvae. This study aimed to evaluate the influence of nutritive characteristics of single microalgal diets in Paracentrotus lividus (Lamarck, 1816) larval development, growth, and condition. Larvae of P. lividus were fed with three monospecific microalgal diets, Rhodomonas sp. (Rho), Dunaliella tertiolecta (Duna) and the diatom Chaetoceros calcitrans (Chae), and their development and growth were analysed until competence. Additionally, the fatty acid (FA) profile of larvae was analysed at competence and compared with the FA profile of the correspondent diet. The three groups of larvae attained competence simultaneously with differences in growth performance. The larvae fed with Chae attained the largest stomach and the shortest post-oral arm. The larvae were able to accumulate long-chain polyunsaturated fatty acids (PUFA), such as docosahexaenoic (DHA, C22:6n − 3), eicosapentaenoic (EPA, C20:5n − 3) and arachidonic (ARA, C20:4n − 6) acids, either by assimilation and retention of dietary FA or by the synthesis from α-linolenic acid (ALA, C18:3n − 3) and linoleic acid (LA, C18:2n − 6). Furthermore, the low DHA/EPA ratio and high EPA/ARA and n − 3/n − 6 ratios of Rho and Chae and the high levels of the β-carotene present in Chae improved larval growth and development. In conclusion, the results indicated that of the three microalgal diets tested, C. calcitrans provided important nutritional characteristics, especially in terms of FA composition and carotenoids, improving P. lividus larval growth and condition.

Molecular and biochemical effects on metabolism and immunity of Hyriopsis cumingii fed with four different microalgae

Hyriopsis cumingii has attracted attention because of its pearl production performance and water purification capacity. Realizing sustainable industrialized culture of H. cumingii or applying it to bivalve biomanipulation for controlling water eutrophication needs urgent studies about the selection of suitable algae and the effects of different microalgae on mussel physiology. To contrast molecular and biochemical effects of high-quality microalgal diets (Chlorella vulgaris, Navicula pelliculosa, and Cyclotella sp.) with toxic Microcystis aeruginosa on metabolism and immune physiology of H. cumingii, levels of related enzymes and genes were analyzed during the 28-day exposure period. Results showed that the Cyclotella sp. diet could significantly (p &amp;lt; 0.05) maintain higher levels of metabolic enzymes (glutamic oxaloacetate transaminase (GOT), glutamic pyruvate transaminase (GPT), pyruvate kinase (PK), and hexokinase (HK)) and genes (CPT1 and LDLR). C. vulgaris and N. pelliculosa treatments significantly (p &amp;lt; 0.05) reduced activities of these metabolic parameters. The M. aeruginosa treatment significantly (p &amp;lt; 0.05) enhanced levels of immune enzymes (alkaline phosphatase (AKP), superoxide dismutase (SOD), and catalase (CAT)) and genes (HcIL-17 and IAP) on day 1 or 7, and there was a significant (p &amp;lt; 0.05) reduction on day 28. Results suggested that Cyclotella sp. was the suitable algae for H. cumingii, followed by C. vulgaris and N. pelliculosa, and toxic algae caused metabolic disorders, immune injury, and poor physiological status. The study has practical significance in the sustainable cultivation of H. cumingii and provides a theoretical basis for bivalve biomanipulation in eutrophic water.

Oils Combination with Microalgal Products as a Strategy for Increasing the N-3 Long-Chain Polyunsaturated Fatty Acid Content in Fish Oil-Free Diets for Meagre (Argyrosomus regius)

Diversification of species and ingredients is essential for further developing aquaculture production. The present study aimed to evaluate the potential of a blend of microalgae oils and poultry oil as total replacers of fish oil in aquafeeds, a fast-growing species for aquaculture diversification, that was shown to require high dietary n-3 LC-PUFA levels. For that purpose, meagre juveniles ( 2.74 ± 0.01 g initial body weight) were fed one of the four experimental diets for 30 days. A control diet (FO diet) was based on 5% fish oil and 7% of rapeseed oil, whereas in the other three diets, fish oil was totally replaced by either poultry oil only (PO diet), or blending poultry oil and one of two commercial algal oils (ED and DD diets). Growth performance, tissue composition, and the expression of genes related to fatty acid biosynthesis, antioxidant defense system, and heat shock proteins were determined. Diets with blends of poultry and microalgae oils supported good growth and feed utilization of meagre. Besides, these diets maintained high DHA tissue contents and good fillet lipid quality indices, like in those fish fed the control diet containing fish oil. Furthermore, the meagre fed ED diet showed the highest expression of gpx, in agreement with the highest dietary polyunsaturated fatty acid content. These results demonstrated the good potential of blending these two commercial microalgae oils with poultry oil to completely replace fish oil cost-effectevily in diets for meagre. In contrast, PO as the sole replacer of fish oil was not able to support fish growth performance and tissue contents of n-3 LC-PUFA, leading to an increased thrombogenic index in fish fillets. Additionally, the low dietay n-3 LC-PUFA content of PO diet upregulated the relative expression offads2 while downregulating gpx compared to microalgal diets.

Microencapsulated diets using thraustochytrids and macroalgae side streams for nursery rearing of Mytilus galloprovincialis spat

AbstractGlobal expansion of bivalve aquaculture can drive sustainable protein production. Inland culture of mussel spat can play an important role in supporting extensive mussel farming. Nursery culture of bivalves is, however, dependent on nutritious, cost‐efficient, and more reliable diets for spat. The aim of this study was to assess the impact of dietary alternatives to commercial algal feeds (Shellfish Diet 1800) on the survival and growth of Mytilus galloprovincialis spat, widely farmed in Europe. Spat (6.8 ± 1.1 mm) were supplied with different diets for 6 weeks: commercial microalgal diet (A), microencapsulated feeds containing a 1:1 blend of the macroalga Undaria pinnatifida and the microalga Schizochytrium (BioBullets; BB), or commercial microalgae and BioBullets combined (ABB). Unsupplemented spat showed no growth and little change in body condition (CI). Spat fed microcapsules grew at comparable rates, and body condition rose at higher levels (shell growth rates: 8.5 ± 3.7 μm day−1; ΔCI: 6.1 ± 1.1%) relative to those fed commercial microalgae (8.5 ± 5.7 μm day−1; ΔCI: 3.3 ± 0.8%). Supplementing microencapsulated feeds with the commercial microalgal diet did not significantly improve growth performances (9.3 ± 2.3 μm day−1; ΔCI: 4.7 ± 1.4%) relative to mussels fed microcapsules alone. Microencapsulated feeds for M. galloprovincialis spat production can significantly reduce nursery costs compared with commercial feeds or cultured microalgae. By sourcing encapsulated algae from aquaculture side streams, microencapsulated feeds can further promote circular economies.

Effect of fresh and spray-dried microalgal diets on the growth, digestive enzymatic activity, and gut microbiota of juvenile winged pearl oyster Pteria penguin

The effects of fresh and spray-dried microalgal diets on the growth, digestive enzymatic activity, and gut microbial community were investigated in juveniles of the winged pearl oyster Pteria penguin. A total of 240 pearl oysters were fed either live or spray-dried unialgal diets of the species Isochrysis zhanjiangensis and Platymonas subcordiformis at a final concentration of 150,000 cells/mL. The experiment was performed over 28 days in triplicate feeding trials under laboratory conditions. At the end of the feeding trials, the hepatopancreas and gut tissue were dissected to quantify the digestive enzymatic activity and analyze the gut bacterial community. The survival rate of the oyster juveniles in all trials was > 90 %. Moreover, the animals fed a spray-dried P. subcordiformis diet exhibited slightly higher shell growth rates. However, the mean shell height and the total wet weight were not significantly different among all experimental groups (P > 0.05). The digestive enzymes amylase, pepsin, and lipase exhibited significantly higher activity levels in oysters fed spray-dried diets than in those provided live microalgae. The different diets also provoked changes in the gut microbiota of the pearl oysters. A total of 27 phyla and 482 genera were detected within all groups examined; the Proteobacteria, Cyanobacteria, Bacteroidetes, and Spirochaetes were the dominant phyla. In general, spray-dried diets exhibited a higher number of operational taxonomic units (OTUs), Chao1, and Simpson and Shannon indices, implying the ability of these diets to promote high microbial biodiversity. Thus, these diets benefitted the maintenance of the intestinal micro-ecological balance and health. The study findings will help optimize intermediate culture technology and management of P. penguin juveniles.

Larval cultivation of Periglypta chemnitzii based on microalgal dietary selection

Periglypta chemnitzii is an edible shellfish whose hardy nature makes it an ideal species for cultivation by aquaculture. The crucial factor determining whether a species is appropriate for aquaculture is successful breeding of the offspring. In this study, we gathered information regarding reproduction and larval cultivation of P. chemnitzii and assessed the suitability of different microalgae diets to serve as a baseline for the purpose of artificial breeding of the offspring. The embryonic and larval development, larval morphological changes, movement, and feeding behaviour of P. chemnitzii were observed under an optical microscope. Eight microalgal species (Chlorella vulgaris, Nannochloropsis oculata, Dunaliella salina, Platymonas subcordiformis, Pavlova viridis, Dicrateria zhanjianggensis, Isochrysis galbana, and Chaetoceros muelleri) were fed to the larvae at different ages to observe the ingestion and digestion by the larvae. Four kinds of single microalgae diets (C. vulgaris, P. subcordiformis, C. muelleri, and D. zhanjianggensis) and three kinds of mixed diets (P. subcordiformis + C. muelleri, P. subcordiformis + D. zhanjianggensis, and C. muelleri + D. zhanjianggensis) were fed to larvae respectively, and their growth and survival rate was monitored. We found that the fertilised eggs of P. chemnitzii hatched into D-shaped larvae after 11 h 26 min; the larvae then developed to the metamorphic stage at 6 days post hatch (dph) and began settlement at 7 dph. The larvae could ingest C. vulgaris, N. oculata, D. salina, P. viridis, D. zhanjianggensis, and I. galbana at 1 dph; some larvae could also ingest P. subcordiformis and C. muelleri at 2 dph. Notably, C. vulgaris and N. oculata were more difficult to digest. Further, mixed diets were more beneficial than single diets for larval growth and survival. In particular, the mixed combination of P. subcordiformis + C. muelleri afforded the fastest growth and the highest survival rate. In single diets, the fastest growth was attained with C. muelleri; whereas the highest survival rate was obtained with P. subcordiformis. Compared with other bivalve molluscs, the clam P. chemnitzii has larger embryos and larger-sized newly hatched larvae, and its embryonic development and planktonic larval stage are also shorter than that of other species. P. chemnitzii larvae were more likely to ingest the smaller, round-shaped microalgal species and digest the species without cell walls, and therefore, D. zhanjianggensis should be the first choice as an opening diet for P. chemnitzii larval cultivation, followed by a mixed microalgal diet of P. subcordiformis + C. muelleri from 3 dph onwards.

Elemental C and N balances evidence stoichiometric adjustments to dietary protein content in growth phenotypes of the Manila clam (Ruditapes philippinarum)

Juveniles from two separately bred families of the Manila clam Ruditapes philippinarum were used to constitute fast (F)- and slow (S)-growing groups by size segregation. The growth phenotypes that resulted from these 4 family*growth category combinations were then used to measure elemental C and N balances in the acute and chronic responses to two different microalgal diets that were isocaloric but differed (x3) in their protein:energy ratios. Both diets were based on the same phytoplankton species (Rhodomonas lens) that were harvested in the exponential (low C:N ratio) or stationary (high C:N ratio) phases of an indoor culture. Aims were to assess the differential acquisition and processing of elemental nutrients according to differences in their dietary availability and the variable requirements set by the growth trends exhibited by different phenotypes. Clams fed the high N diet achieved the highest C and N balances through a combination of higher feeding rates and absorption efficiencies of overall organics. However, the main differential effects were associated with increased absorption efficiencies for N relative to C, which were particularly observed in clams subjected to chronic N deficit in the diet. This occurred in all growth phenotypes and resulted in the partial homeostatic regulation of nutrient imbalance operating at the preabsorptive level. Further adjustments occurred at the postabsorptive level with increased N disposal in the form of ammonia excretion and the resulting decrease of metabolic C:N indices recorded in clams fed the high N diets. The main phenotypic differences were observed in the intrafamily (F vs. S growth groups) rather than in the interfamily comparisons, with F clams exceeding the absorption rate of nutrients (both C and N) of S clams by 50%. Physiological responses to the acute dietary change were found to be faster in F clams, indicative of a higher plasticity of this phenotype. Whereas, stoichiometric adjustments by S clams resulted in higher N release through excretion, suggesting less efficient protein turnover.