Chirocentrodon bleekerianus (TELEOSTEI: CLUPEIFORMES: PRISTIGASTERIDAE), A SMALL PREDACEOUS HERRING WITH FOLDED AND DISTINCTIVELY ORIENTED PREY IN STOMACH

Predaceous fish-eating species of the order Clupeiformes have a large mouth with well-developed teeth, and reach the greatest sizes within their families (up to 90 cm). We found that the pristigasterid Chirocentrodon bleekerianus, a small clupeiform (about 10 cm) from the tropical SW Atlantic, is able to prey on proportionally large clupeoid fishes and caridean shrimps. Fish preys are folded in the stomach of this herring, their heads and tails pointing toward the predator’s head. This distinctive orientation of fish prey is also recorded for some small to medium-sized, fish-eating species of the tropical freshwater order Characiformes with canine-like teeth similar to those found in C. bleekerianus.


INTRODUCTION
Most fish species of the order Clupeiformes (herrings and anchovies) feed on planktonic organisms.These plankton-eaters have long and numerous gill rakers and a small mouth with tiny teeth (Whitehead, 1973;Whitehead et al., 1988;Nelson, 1994).Predaceous fish-eaters are found in all clupeiform families but Denticipitidae (Whitehead, 1985;Whitehead et al., 1988;Nelson, 1994).Piscivorous herrings are among the largest species within their families and generally have a large mouth with well-developed teeth (Goulding, 1980;Whitehead, 1985;Nelson, 1994).
The pristigasterid dogtooth herring, Chirocentrodon bleekerianus, is a small-sized clupeiform, reaching 11 cm in total length (TL), found in the tropical SW Atlantic from the West Indies to southern Brazil (Whitehead, 1973;Figueiredo & Menezes, 1978;Carvalho-Filho, 1994).We found no studies on the feeding habits of C. bleekerianus.However, its large mouth with welldeveloped and canine-like teeth (Whitehead, 1973) indicates that this herring may have piscivorous habits (Carvalho-Filho, 1994).
We analysed stomach contents of dogtooth herrings collected off the coast of Brazil, to examine the hypothesis that this small clupeid may prey on fishes.Although not intended as a dietary study, our results show that C. bleekerianus has predaceous habits and preys on fishes, an unrecorded habit among small species of clupeiforms (Whitehead, 1973(Whitehead, , 1985;;Nelson, 1994).

MATERIAL AND METHODS
We examined samples of C. bleekerianus collected with fence and trawl nets between 5:30 h and 9:00 h, off the coast of São Paulo (n = 35), Espírito Santo, and Bahia (n = 11), Brazil, in May and August 1996, and January 1997.Up on collection, the fish were fixed in 10% formalin and later preserved in 70% ethanol.Stomach repletion (SR) was visually estimated based on fullness state, using a four-point scale (Gramitto, 1999).Food items found in the stomach were examined under a stereomicroscope and clumped into two broad categories (fishes and shrimps), and their frequencies of occurrence were calculated (see Hyslop, 1980, for procedure).Standard length (SL) of the dogtooth herring and total length (TL) of undigested or partly digested prey were measured with tenths of millimeters precision (we used total instead of standard length for the prey animals, as both fishes and shrimps were found in stomachs).The position of fish prey in stomach was determined by opening the stomach wall in situ and making a sketch of the position of prey relative to the predator (Fig. 1).Voucher specimens and their stomach contents are in the Museu de História Natural, Universidade Estadual de Campinas (3943)(3944)(3945)(3946)(3947)(3948).
Chirocentrodon bleekerianus is able to prey on proportionally large fishes (up to about 50% of its own length) and its shrimp prey may reach a large size as well, an additional indication of its ability to handle large prey.The folded and distinctively oriented prey fish in the stomach of the dogtooth herring is probably due to the large size of this prey type.In the wolf herrings Chirocentrus dorab and C. nudus, large prey fish is found folded in the stomach (Luther, 1985) in a way similar to that recorded here for C. bleekerianus.The clupeids Cynothrissa and Odaxothrissa, the pristigasterid Chirocentrodon, the chirocentrid Chirocentrus, and the engraulid Lycothrissa, all have in common well developed canine-like teeth (Whitehead, 1973;Nelson, 1994).This is an unusual trait among clupeiforms and is likely related to a piscivorous diet.At least in Chirocentrus and Chirocentrodon, these teeth may play a role in folding and orientation of fish during prey handling and swallowing (shrimps, regardless of size, already have a propensity to fold).
Distinctively oriented folding of fish prey in the stomach is also recorded for the mainly piscivorous genera Cynopotamus, Galeocharax, and Acestrocephalus, of the large tropical freshwater order Characiformes (Menezes, 1976;IS, pers. obs.).These small to medium-sized characids (up to 25 cm TL) have curved and developed canine-like teeth on the premaxilla, and laminar and spiny gill rakers  (Menezes, 1976).Folded fishes in the stomachs of these characids are oriented towards the predator's head in a way similar to that recorded here for Chirocentrodon (IS, pers. obs.).This type of prey folding and orientation is likely to occur during capture, with manipulation of prey before ingestion (Menezes, 1976), as headfirst swallowing is a common attribute among piscivorous fishes (Reimchen, 1991;Helfman et al., 1997).The distinctively oriented folding of prey fishes in smallsized clupeiform and characiform predaceous piscivores is a remarkable instance of convergence, as these two fish groups are phylogenetically unrelated (Nelson, 1994).