The role of prey detection in the selection of prey by pinfish Lagodon rhomboides (Linnaeus)

Abstract

Selective feeding by fishes may be due in part to the conspicuousness of particular prey types; certain prey may be disproportionately detected by fish and thus could be subject to a greater risk of predation. In laboratory experiments designed to test the relative importance of chemoreception, vision, and prey activity in the process of prey detection, I allowed pinfish Lagodon rhomboides (Linnaeus) to choose among various seagrass-meadow-associated infaunal and epifaunal prey [ Melita, Cerapus, Caprella (amphipods); Hippolyte (shrimp); Americonuphis, Nereis (polychaetes); and Clytia, Sertularia (hydroids)]. In laboratory trials, pinfish approached individual prey enclosed in clear glass tubes with an open end (covered with 50-μm mesh Nitex screen to allow water exchange) that were provided with sand and seagrass blade substrata. Within each trial, one prey species was offered in an array consisting of an unaltered tube and tubes that had been manipulated to prevent detection of the enclosed prey using vision (opaque sides), olfaction (sealed tops), or both senses (opaque sides and sealed top). Pinfish most frequently approached prey in the clear-sided, screen-topped tubes and least frequently approached tubes with opaque sides and sealed tops; the tubes with sealed tops and clear sides or screened tops and opaque sides were approached with intermediate frequency. Approach frequencies were similar for all prey types tested. It appears that vision and chemoreception were used jointly by pinfish to locate the enclosed prey. In a second series of prey choice experiments, pinfish were offered four prey types (amphipods, shrimp, polychaetes, and hydroids), either live or freshly killed, in clear glass tubes with screen tops to determine if inactive, but otherwise similar prey, were approached as frequently as active prey. All prey types tested were approached with similar frequency; however, live prey were approached more frequently than dead prey (although not significantly more frequently). Small, mobile epifaunal prey (i.e., amphipods and other microcrustaceans) should be disproportionately detected on the seagrass blades by pinfish in the field and thus may be subject to a greater risk of predation than sessile prey.