Feeding ecology of Anableps anableps (Actinopterygii: Cyprinodontiformes: Anablepidae) off the north-eastern coast of Brazil

Abstract

Background. Diets, feeding ecology, and feeding strategies of several mangrove fish species have not been studied off the coast of Maranhão, which is exposed to a significant tidal regime. This includes also the largescale foureyed fish, Anableps anableps (Linnaeus, 1758). The aim of the presently reported study was to characterize diet, feeding strategies and seasonal patterns of the diet of A. anableps. Materials and methods. The sampling was carried out in São Marcos Bay between May 2007 and April 2008 using block nets. The stomach fullness index was used for stomach content analysis. Dietary items were identified and parameters such as the prey-specific abundance and the frequency of occurrence were calculated. The feeding strategy was analysed with the aid of the Costello diagram. Seasonal patterns in the feeding behaviour and similarity in diet composition were also analysed. Results. Diet composition did not differ between seasons but stomach fullness was greater in wet season months. The diet of A. anableps consisted of a mixture of epiphytic microalgae and macroalgae, insects, crustaceans, molluscs, fishes, and digested material such as mud and detritus. Insects represented the greatest richness among the food items. The Costello diagram revealed that A. anableps had a generalist feeding strategy, with a dominance of macroalgae, insect, and fishes. A broad niche was also found, as indicated by a strong association with interphenotypical components. Conclusion. This study presents data that confirm the forage characteristic of A. anableps and the influence of seasonality on its feeding behavior, in which the species takes advantage of the greater availability of food due to runoff and the larger flooded area, during the wet season. Further studies should be carried out to determine the energy needs of this species in satisfying its reproductive demands as well as the abundance of food resources in the surrounding environment and the confirmation of the generalist feeding strategy.

Light-induced shifts in opsin gene expression in the four-eyed fish Anableps anableps

“…The commercial diet provided for the animals in captivity, however, differs from their diet in natural settings. In the wild, the stomach content of A. anableps ranges from micro and macroalgae, insects, crustaceans, molluscs, fishes, to mud and detritus (Figueiredo et al, 2019). While we cannot rule out a potential feeding behavior of food content impact on opsin gene expression, we have no knowledge of a documented link between the former and the latter.…”

Acusicola rochai n. sp. (Copepoda: Ergasilidae) parasitizing Anableps anableps (Anablepidae) from the Amazon Coast, with a key for Acusicola spp.

“…Species of this genus are commonly known as ‘foureyes’ fish due to their unusual morphology: eyes divided into two portions, each with an individual pupil, enabling surface-swimming individuals to simultaneously focus on images above and below water. Anableps anableps is commonly found inhabiting freshwater and mangrove coastlines in Brazil, primarily in the Amazon River Delta, Northeast coast, and is frequently used as a subsistence resource by some populations (Nelson et al ., 2016; Figueiredo et al ., 2019; Rodrigues et al ., 2021; Froese and Pauly, 2024). Despite its local importance and peculiar aspect, only five species of parasitic crustaceans have been reported on An.…”