Studying the phototactic response of our Adriatic sturgeons 19.07.21

To assess the fitness of our Adriatic sturgeons (Acipenser naccarii) we started to investigate the response to diverse stimuli. Among them, we chose to further explore the response to light (phototaxis) in our inbred and outbred stocks. A positive phototactic response can be linked to higher success in finding new sources of food, since many potential preys are themselves attracted to light, like zooplankton, little crustaceans, and insect larvae.
The phototactic response has been studied in other sturgeon species showing different behaviours depending on the species. For example, the prelarvae of Siberian sturgeon (Acipenser baerii) showed a positive phototactic response after the firsts days post-hatch. Instead, other species like the Russian sturgeon (Acipenser gueldenstaedtii) and ship sturgeon (Acipenser nudiventris) showed a negative phototactic response. 
For the Adriatic sturgeon, no studies are nowadays present involving this behaviour and we could follow the response to light of these animals several months after the hatching. In the firsts weeks post-hatch, all the individuals tested in our stocks showed a positive phototactic response. Several months after, positive phototaxis was still present in most individuals. For this reason, we decided to perform phototaxis tests taking 20 individuals of different sizes, from each stock. The weight of each fish was measured. During the test, we maintained a constant temperature of 17°C, and the individual was placed at the extremity of a 2-meter-long covered tank. Then the other tank’s extremity was uncovered letting the light passing through and creating an illuminated area to attract the individual, allowing us to measure the time taken to reach the end of the tank. Possibly, this behaviour can be related to the health condition of the individual and can be used as a fitness indicator. These tests aim to assess if differences in the response’s time are present for individuals of distinct stocks (inbred versus outbred) or distinct size classes (fast growing versus slow growing).

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