Relationship between gape size and feeding selectivity of fish larvae from a Neotropical reservoir

Larvae feeding selectivity of Iheringichthys labrosus, Hypophthalmus edentatus and Plagioscion squamosissimus was assessed, examining the role of mouth gape in prey selection. Fish larvae were sampled in the Itaipu Reservoir (Brazil-Paraguay). Iheringichthys labrosus and H. edentatus larvae, with small and similar gape sizes, exhibited slightly different diets; I. labrosus preferred cladocerans (Bosmina hagmanni, Bosmina huauriensis and Bosminopsis deitersi) and the rotifer Brachionus calyciflorus. Hypophthalmus edentatus, however, primarily ingested the cladocerans B. hagmanni, Ceriodaphnia cornuta, Daphnia gessneri and Diaphanosoma spinulosum. Plagioscion squamosissimus, with a greater gape size, preferred Calanoida. The mechanistic processes that determine food selectivity of fish larvae in temperate aquatic systems were similar in the Neotropical system. The trophic spectrum of these species is characterized by small- to intermediate-sized prey. Plagioscion squamosissimus larvae, which have larger mouths, exploit primarily larger prey differing from the most abundant species or size classes; consequently, their diet is quite different from I. labrosus larvae and modestly similar to H. edentatus larvae, opportunistic feeders that they eat more abundant prey.