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Abstract

Cryptobenthic fishes are an important part of the fish community whose role has often been overlooked in the past. Due to the lack of knowledge, cryptobenthic fish species have been considered as rare and not numerous in the past. However, recent studies show quite the opposite, as due to their high abundance in the environment, they are very important and they are able to shape the ecosystem. Despite their importance, the cryptobenthic fish fauna of the Adriatic, as well as the Mediterranean Sea in general, is poorly known, especially regarding their ecology. The purpose of the thesis was to review the occurrence of the cryptobenthic fish fauna in the Slovenian part of the Gulf of Trieste (North Adriatic) and to deepen the knowledge on the ecology of the Gobiesocidae family which is one of the least known fish families in the Mediterranean Sea.
In the present study, a total of 12 cryptobenthic fish species belonging to four fish families were confirmed in the Slovenian sea: Gobiidae, Gobiesocidae, Blenniidae and Clinidae. Three species (Chromogobius quadrivittatus, Odondebuenia balearica, Thorogobius ephippiatus) were observed for the first time in Slovenian territorial waters. The family Gobiesocidae was represented by three species: Lepadogaster lepadogaster, L. candolii and Apletodon incognitus.
We have shown that the studied species have different habitat preferences, as well as depth distribution. Species of the genus Lepadogaster occurred mainly on the rocky bottom, where L. lepadogaster was found in the mediolittoral and upper infralittoral, and L. candolii occurred mainly deeper in the infralittoral. Both species occurred beneath the stones under which pebbles appear as a substrate. A. incognitus occurred deeper than the other two species, and its occurrence is related to the seagrass meadows where it inhabited mostly empty shells of oysters. Seashells were occupied also by L. candolii, which in small proportion occurred in seagrass meadows too.
Fish nests were also found in shelters, which were observed in L. lepadogaster from the end of March to the end of May and in A. incognitus from mid-May to mid-July. The nest of L. candolii was observed only once in May.
For the purpose of studying clingfish diet, a method based on faecal pellets has been developed. Diet study has shown that all three species are opportunists whose most important prey are crustaceans. Benthic copepods, amphipods and decapods were the most important prey groups.
Clingfishes are also important intermediate and final hosts of different parasites. In total, three groups of external parasites were found on the clingfishes: parasitic larvae of the family Gnathiidae (Isopoda) and parasitic copepods of the families Caligidae and Lernaeopodidae. Internal parasites were represented mainly by flatworms (Trematoda).
The research provides important information on the occurrence of cryptobenthic fish species of the Slovenian sea and basic data on the ecology of the three clingfishes. With this knowledge we would like to contribute to the understanding of the ecology of neglected species whose role in the ecosystem is far from negligible but of utmost importance.