What to choose when the best preference is not available: does the Nile tilapia follow a linear sequence of preferences?

Preference tests have been applied to detect better welfare conditions for the animals. Among these tests, the available choice options are variable and thus, the best preferences may not be included. Considering welfare purposes, it is relevant to know whether the animal would select a second option as a preference in this situation, which could be offered when the best preferences are not available. Here, we evaluate whether Nile tilapia fish (Oreochromis niloticus) follow a linear sequence of preference responses when selecting background colors. We found that when a fish's most preferred option was unavailable, this animal selected less intensely one of the remaining options as a new preference. However, surprisingly, the new preference was not predominantly the previously second selected option. Such a finding could not be explained in terms of intensity of the responses when the mostly preferred option was available or not. These data corroborate that changing the scenario where the preference is being tested affects animal decision for the remaining available options. That is, the environmental context is important for the fish to evaluate their preferred options. Preference tests have been used to detect better welfare conditions for the animals, but the choice options are variable in such tests and thus, the best preferences may not be included as options. Knowing whether the animal would select the second option as the new best preference in such conditions is important for welfare purposes, because if this is the case, the second option could be offered whether the best preference is unavailable. Here we demonstrated that this is not necessarily the case and thus, changing the scenario where the preference is being tested by removing the best option affects animal decision for the remaining available options, which has implications for welfare purposes.