Biotic vs. Abiotic Substrate: Habitat Choice in Three Baltic Fish Species

The study aimed to determine the habitat preferences of the round goby (Neogobius melanostomus), European flounder (Platichthys flesus), and three-spined stickleback (Gasterosteus aculeatus). Two types of substrate were included in the experiment—biotic and abiotic. The abiotic substrate contained no living organisms but had a physical structure very similar to the biotic substrate. Observations were conducted in day and night cycles, repeated twice. Observation of each fish lasted 150 min. The time spent on each substrate and the number of substrate changes by each individual were determined. Based on the results obtained in this study, a preference for the biotic substrate during the day was observed in all three fish species. At night, only the European flounder showed a clear preference for the abiotic substrate. The round goby was more active at night, changing substrate twice as often as during the day. Individuals of this species also showed greater activity, i.e., additional behaviors. The number of substrate changes by the European flounder and the three-spined stickleback did not depend on light conditions. Sticklebacks exhibited high locomotor activity both during the day and at night, changing substrate significantly more often than the other species. None of the analyzed species completely avoided the abiotic substrate, suggesting that fish-habitat restoration through artificial structures may be viable.