Shelter or complexity? Nile tilapia (Oreochromis niloticus) preference for enrichment structures is a matter of time and frequency of visits.

Abstract

Assessing fish preferences for resources may be an interesting approach to select environmental enrichments to improve their welfare. However, different operational variables may end up indicating distinct preferences. Here we investigated whether Nile tilapia (Oreochromis niloticus) express different preferences for environmental enrichment structures providing shelter and complexity by analyzing such responses based on time spent or frequency of visits as operational variables. We performed repeated choice tests with a clay pot providing single “shelter” and a suspended “complex” structure of intertwined ropes to infer the preferences of each individual (n = 44). Considering the frequency of visits in the enrichments, a similar number of fish preferred “shelter” or “complexity”, and there was no difference for the intensity of these responses. However, for the time spent at the enrichments, “shelter” was more intensely preferred. Moreover, there were individuals expressing opposite preferences depending on the operational variable, and most of them preferred “shelter” by time spent in it. In conclusion, Nile tilapia usually prefers to visit “shelter” and “complexity” similarly, but staying longer at the “shelter”. Thus, the frequency of visits to a resource or the time spent at one place, variables commonly used to infer animals’ preferences, can reflect different outcomes.