Supervisors info:
Δρ. Αθηνά Οικονόμου-Αμίλλη Ομ. Καθηγήτρια Τμήμα Βιολογίας ΕΚΠΑ (Επιβλέπων),
Δρ. Ιωάννης Κλαδάς, Καθηγητής Πανεπιστημίου Πατρών, Τμήμα Ζωικής Παραγωγής, Αλιείας και Ιχθυοκαλλιεργειών,
Δρ. Εμμανουήλ Φλεμετάκης, Καθηγητής Γεωπονικού Πανεπιστημίου Αθηνών, Τμήμα Βιοτεχνολογίας.
Summary:
Microalgae form the basis of the food web in aquatic environments and are the basis of productivity in the majority of such ecosystems, including lagoons and other coastal transitional systems. The organisms of coastal ecosystems are adapted to cope with the strong and sudden fluctuations in the environmental conditions prevailing in these systems, demonstrating high productivity and usually producing secondary metabolites, which may have high nutritional and biotechnological value. In the present study, five strains of microalgae (LOG 1-1, VON 1-3, MPA 1-3, D4, D5) isolated from Greek transitional ecosystems, the lagoons of Logarou, Voda, Bastia and the salt ponds of the Great Embolus region were used. These strains, which are deposited in the Athu-Al microalgal bank, were characterized using both molecular and classical classification methods (optical and electron microscopy) as well as basic biokinetic and biochemical characterization (culture kinetic study, biovolume, content of primary metabolites and pigments). The results were used to evaluate their cultural and biotechnological interest. Also the data on the growth and nutritional value of these strains provide useful information for their use as feed in trophozoan breeding.
Rotifers are one of the most widespread zooplankton groups used as live food for rearing larval fish in marine fish farms, with the genus Brachionus being widely used in hatcheries due to its relatively easy and low cost of rearing. In a first stage, rearing experiments were conducted on a Greek strain of the rotifer Brachionus plicatilis (Phyl: Rotifera, Class: Monogononta, Order: Plioma, Family: Brachionidae, Genus: Brachionus, Species: Brachionus plicatilis) which was obtained from a collaborating laboratory of the University of Patras under the supervision of Professor Hotos using the above mentioned strains as food.
More specifically, after the acclimatization of the rotifers, rearing experiments were carried out using the five microalgal isolates as a food source and the Dunaliella tertiolecta UTEX 999 strain as a reference strain. All algae used were grown in 5 L volume cultures and cell density measurements were taken every 24 hours. Rotifers cultures were carried out in 1 L volume and 2 L plastic containers were used for better distribution and gas exchange while every 24 hours measurements of rotifers population density, total number of eggs and percentage of females laying eggs were made.
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After obtaining the above measurements, using the biovolume and cell density of the microalgae culture in combination with the cell density of the rotifers culture, the appropriate amount of feeding was calculated and the feeding of the rotifers was carried out. This step was deemed necessary to keep the biomass added per rotifers constant as the sizes of the microalgae used varied and the cell densities of both the microalgal and rotifers cultures changed daily.
Based on the results of the above experiment, the two strains (LOG 1-1 and D4), stood out as they led to growth that was comparable or in some cases even better than that achieved using the reference microalgae (Dunaliella tertiolecta UTEX 999), the strains (VON 1-3 and D5) led to little growth and the strain (MPA 1-3) failed to support the growth of the rotifers culture.
Apart from the successful rearing of rotifers, a very important parameter for their use in hatcheries is their nutritional value, which plays a key role in the proper development of the early life stages of farmed fish. For this reason, an enrichment protocol for the rotifers under study was tested using the six aforementioned microalgal strains. The purpose of the aquaculture enrichment process is to increase the nutritional value of rotifers intended for feeding the early developmental stages of fish, molluscs and other cultured organisms. Fatty acids, in particular polyunsaturated fatty acids (PUFA), are one of the most important objectives of enrichment. For this reason, an analysis of the fatty acid composition of microalgal strains as well as of rotifers after a short period of feeding with excess biomass from the strain in question was carried out. It is noteworthy that all the microalgae strains used resulted in a significant increase in the total fatty acid content of the rotifers under study (increase from 33 to 182 %) as well as enrichment with remarkable amounts of important polyunsaturated fatty acids such as linoleic acid (LA) and alpha-linolenic acid (ALA).
Keywords:
Microalgae, Rotifers, Cultivation, FAMEs, Aquaculture
