Aquaculture Europe 2021

October 4 - 7, 2021

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Add To Calendar 06/10/2021 14:30:0006/10/2021 14:50:00Europe/LisbonAquaculture Europe 2021NEW COMMERCIAL MICROALGAE DIETS FOR BIVALVES APPLIED TO PORTUGUESE OYSTER Crassostrea angulataSidney-HotelThe European Aquaculture Societywebmaster@aquaeas.orgfalseDD/MM/YYYYaaVZHLXMfzTRLzDrHmAi181982

NEW COMMERCIAL MICROALGAE DIETS FOR BIVALVES APPLIED TO PORTUGUESE OYSTER Crassostrea angulata

 

Patrícia Diogo1, Gonçalo Bastos1, Cristiana Gastão2, João Carneiro2, Ana Marreiros3,4, Alexandre Rodrigues1, António Falcão2, Victória del Pino1 and João Navalho1

 

1Necton, S.A., Belamandil, 8700-152 Olhão, Portugal, 2Viveiros Rio Mira LDA, Roncanito-Algoceira, 7630-013 Odemira, Portugal, 3Department of Biomedical Sciences and Medicine, University of Algarve, 8005-139, Faro, Portugal, 4Algarve Biomedical Center, Campus Gambelas, 8005-139, Faro, Portugal.

E-mail: patricia.diogo@necton.pt

 



Introduction

Few commercial multialgal diets formulated for bivalve’s are available and generally lack important microalgae difficult to produce industrially, such as Tisocrysis lutea and Skeletonema costatum. Microalgae production in hatcheries is expensive (30-50% of total costs)1, labour intensive and subjected to productivity fluctuations. Therefore, commercial microalgae diets are a major asset. The objective of a nursery is to achieve high larvae quantities of good quality and improve juvenile growth. Good quality nutrition is essential for broodstock maturation in order to generate high quality gametes and offspring, and to optimize juvenile growth. Oysters (Crassostrea spp.) depict the world’s most produced mollusc species. Portuguese oyster (Crassostrea angulata) has a high potential for aquaculture, although its natural populations suffered a decline in the past decades. Therefore, C. angulata production is important for aquaculture, being simultaneously relevant for natural populations restocking and conservation. Commercial microalgae diets can improve aquaculture management. This work aims to develop commercial diets for bivalves, formulated with a blend of microalgae species commonly used in aquaculture for oyster nutrition applied to Portuguese oyster broodstock and juveniles.

Material and methods

Pilot liquid concentrated products (8% of dry weight-DW) of industrially produced microalgae were formulated. Diet 1 contained Tetraselmis sp., Skeletonema sp., Tisocrysis lutea and Pavlova sp. (8/16:6/16:1/16:1/16), while diet 2 was formulated with Skeletonema sp., Tisocrysis lutea (T-ISO clone) and Tetraselmis sp. (11/16:5/6:1/16). Diets´ biochemical analysis was performed. Controls were based on live algae: microalgae for broodstock were produced on site (Tisocrysis lutea, Tetraselmis sp. and Skeletonema sp.); juveniles from the control group were grown in Mira river (Odemira, Portugal) feeding on the naturally occurring microalgae. Animals were fed daily with an amount equivalent to 4% of the oyster dry meat (g) in DW of microalgae (mg). A preliminary experiment was performed in C. angulata broodstock, where the control and Diet 2 groups were conditioned in duplicate (each replica n=20) at 20±1°C, 20‰, being evaluated the oysters’ weight, biometry and condition index. Gametes were extracted by gonadal incisions. Oocytes from females of control (n=2) and diet 2 treatment (n=2) were fertilized in vitro with sperm from a single control male in triplicate, to compare oocyte quality between treatments in this preliminary approach. Sperm concentration was quantified with a Neubauer chamber. The evaluation of oocyte fertilization and larvae survival (48 hours post fertilization) was conducted. Juveniles were directly placed in nets on the natural environment as control in duplicate (n=250 oysters per replica) or conditioned indoors and fed with Diet 1 and 2 for 3 months (duplicate, n=250). Juveniles were sampled (n=50) throughout time for measurements (survival, weight, length and width) (total n=3175) and collected for condition factor evaluation (n=266). The environmental conditions were daily monitored. IBM SPSS Statistics 26.0 software was used for statistical analysis, one-way ANOVA was used to compare differences between juvenile groups and Student´s t-test for in vitro fertilization data (p<0.05). A cluster analysis was applied to juvenile data and, subsequentially, a decision tree approach allowed to understand juvenile’s growth pattern in the different size groups of oysters in the treatments.

Results

Proximal composition showed the proteins, lipids and ashes content of Diet 1 (23, 10.9, 63%) and Diet 2 (9.9, 2.1, 82.2%) respectively. The broodstock established in control group was heavier and had higher length (94.4±15.6g, 83.2±7.2mm) compared to Diet 2 treatment (56.8±18.5g, 69.7±7.5mm) in the beginning of the experiment. Preliminary results of oocytes obtained by the broodstock fed with Diet 2 showed 86.3±10.6% of fertilization rate, which was significantly lower compared to control (93.9±8.6%). For juvenile there were no significant differences in the survival rate in all treatments. Juveniles fed with Diet 2 showed higher and less variable weight and length gain (R2=0.8542, R2=0.7219) than Diet 1 (R2=0.3101, R2=0.4233) and control (R2=0.1469, R2=0.3733). Even though oysters in the control started with higher weight and biometric measurements, at the end of the trial there were no significant differences in all treatments regarding the wet weight and height (n=3175). To the group of juveniles collected for condition factor index evaluation, a K-means cluster analysis was applied to aggregate oysters by size groups (large, medium and small size groups). A decision tree approach was applied through a CHAID method to the clusters obtained, with wet weight as dependent variable (n=266). In small size oyster cluster group, Diet 1 and control promoted the highest wet weight below 40.6mm, while above this length, Diet 2 improved oyster’s weight. In medium size oysters cluster group below 40.6m (33.5-34.8mm) Diet 1 showed the highest wet weight. In large size oysters cluster group below 40mm, Diet 1 and control had the highest weight, while in oysters above 40mm Diet 2 showed the highest value.

Discussion

Preliminary tests in C. angulata broostock showed that oysters fed on Diet 2 had an equivalent weight to the control group. Obtained oocytes with Diet 2 treatment exhibited high fertilization rate and larvae survival, although significantly lower than the control, which can be explained by the low number of animals. Therefore, in the future, a large-scale test will be performed with Diet 2 in oysters maturation and larvae quality. The growth of juvenile oysters with diets is more constant throughout time than in control, which suggests that natural environmental fluctuations promote variability in microalgae species and abundance, impacting oyster growth. In oysters below 40.6 mm, Diet 1 promoted equivalent weight to the natural environment. Higher protein and lipids content in Diet 1 can support the high requirements for growth of smaller oysters. Prototype Diet 2 promoted high and steady growth in Portuguese oyster juveniles. This is a balanced diet based on the microalgae species and proportions used in oysters hatcheries2. To enhance wet weight gain in Portuguese oysters a dietary protocol based on Diet 1 until 40.6 mm and Diet 2 after this length can be used. In conclusion, the formulation of microalgae diets, such as Diet 2, specifically developed for bivalves can simplify and support nurseries management.

References

1.Willer, D. & Aldridge, D. C. Microencapsulated diets to improve bivalve shellfish aquaculture. R. Soc. Open Sci. 4, (2017).

2.Anjos, C. et al. Broodstock conditioning of the Portuguese oyster (Crassostrea angulata, Lamarck, 1819): influence of different diets. Aquac. Res. 48, 3859–3878 (2017).