Πειραματική συγκριτική διερεύνηση σε ελεγχόμενο περιβάλλον των βασικών βιολογικών παραμέτρων των αρπακτικοειδών κωπηπόδων των γενών tisbe και tigriopus

Abstract

ABSTRACT This dissertation concerns experimentation on two marine harpacticoid copepod species isolated from coastal lagoonal areas of the Messolonghi lagoon (W. Greece). Based on the relevant literature the first species belongs to Genus Tisbe (presumably Tisbe holothuriae) and the second to Genus Tigriopus (presumably Tigriopus fulvus). As we were unable to make exact identification at the species level by using molecular markers and in order to eliminate any uncertainty about their taxonomy we chose to refer to them with only their Genus name Tisbe and Tigriopus. Overall, from preliminary cultures in the laboratory, both species proved very sturdy and presented ease in handling, with rapid population increase in various vessels accepting all kind of microalgal food. The main purpose of the research was to find their suitability for mass culture in order to be candidates as live food in fish hatcheries.The experimentation included 3 sections. 1st was about fecundity as of the total production of nauplii from each egg-sac bearing female, 2nd the salinity tolerance of the copepods in an extreme range from fresh water till the extreme of 140 ppt, 3rd the influence of 5 cultured microalgae on their population growth. In terms of salinity tolerance as investigated with the probit method it was found that both species presented an impressive survival of 100 % (or almost 100 %) in a wide range of salinity ranging in 20-80 ppt for Tigriopus(LC50(95% CL) = 132 ± 5,35 ppt) and 30-70 ppt for Tisbe (LC50(95% CL) = 93 ± 3,23 ppt). The range probably can be wider if the copepods could had been previously gradually acclimatized in the tested salinities instead of being abruptly introduced in it from the standard salinity of 35 ppt (dictated from the probit method). Thus Tigriopus is more halotolerant than Tisbe especially in lower salinities (brackish water) with LC50 = 1 ppt vs LC50(95% CL) = 15 ± 2,41 ppt respectively. In salinity of 35 ppt where both species seem to perform their biological activities in natural terms, fecundity of each egg bearing females was estimated as hatched nauplii per day till the exhausting of the eggsac. Both species presented a gradual hatching of the eggs for a period extending several days and their productivity was almost the same with mean values 34,6 ± 1,95 nauplii per eggsac for Tisbe and 34,4 ± 2,83 nauplii per eggsac for Tigriopus. These values of nauplii production are quite promising in terms of mass culturing as compared with the those in the literature and probably can be further increased with optimization of culture conditions. In the feeding with microalgae experiment using 3 chlorophytes (Tetraselmis, Dunaliella, Asteromonas), 1 haptophyte (Isochrysis) and 1 cryptophyte (Rhodomonas) the 28 days experimentation using 1 gravid female per 4 ml cell (25 replicates) resulted in population increase with a maximum of 830 individuals for Tetraselmis fed Tigriopus and a minimum of 137 ind. for Isochrysis fed Tigriopus. All algae proved effective on the population growth with Tetraselmis and Asteromonas the most efficient especially for Tisbe fed with Asteromonas (SGR-r=0,11) and Tigriopus fed with Tetraselmis (r=0,13). Thus flagellated microalgae can be effective in copepod raising.