Copeia, 1990(3), pp. 665-673 Caudal Eyespots as Deterrents against Fin Predation in the N eoptropical Cichlid Astronotusocellatus KIRK O. WINEMILLER Astronotus ocellatus and several other large cichlid fishes of South America exhibit bright ocelli, or eyespots, near the base of the caudal fin. Astronotus ocellatus sympatric with fin-nipping piranhas of the genus Serrasalmus shows less extensive fin damage that sympatric cichlids of similar size that lack distinct caudal ocelli. Ecological data and observed interspecific behavioral differences support the hypothesis that eyespots reduce piranha attacks by confounding visual recognition of the prey's caudal region. Dense scalation of the unpaired medial fins, especially the caudal fin, masks visual cues for fin recognition, further enhancing head mimicry by the caudal region. The hypothesis that caudal ocelli in A. ocellatus, and perhaps other large cichlid fishes, function primarily as eye mimics for defense against fin predators is more parsimonious than Zaret's earlier "inhibition of cannibalism" hypothesis. F ISH fins are a principal food resource for closely (Sazima and Zamprogno, 1985; Nico and many characids of the South American Taphorn, 1988; Winemiller, 1989b). Fishes genera Serrasalmusand Pristobrycon(Machado- captured from lowland aquatic habitats shared Allison and Garcia, 1986; Northcote et al., 1986; by Serrasalmusspp. commonly show extensive Nico and Taphorn, 1988; Winemiller, 1989b). fin damage, particularly around the caudal I:e- Fins provide a seemingly abundant, rapidly re- gion (Northcote et al., 1986; Nico and Tap- newable food resource for these diverse pira- horn, 1988; Winemiller, unpubl.). nhas. Fin-nipping is most prevalent among sub- Fin-nipping must have a serious negative im- adult and small adult size classes of most pact on growth and survival of prey. For ex- Serrasalmus spp. that have been investigated ample, damaged fins of captive fishes are more @ 1990 bv the American Societv of Ichthvoloilists and Hernetolo.nsts 666 COPEIA, 1990, NO.3 susceptible to bacterial and fungal infection MATERIALS AND METHODS (Reichenbach-Klinke and Elkan, 1965). Fin damage adversely affects swimming perfor- Studysites.-Most specimens used in the present mance, which in turn hinders feeding and es- analysis came from Caiio Maraca, a swamp/ cape efficiency (Sazima and Pombal, 1988). In creek of the Rio Apure drainage of the llanos addition, fin damage impacts the fish's energy in the state of Portuguesa, Venezuela. Full de- budget negatively, since matter and energy scriptions of the Caiio Maraca environment and would be diverted away from gonadal devel- methods of collection are given by Winemiller opment and overall somatic growth, and di- (1987, 1989a, 1989b). Fishes were collected rected toward fin regeneration. Even the dom- monthly during 1984, preserved in 15% for- inance status of individuals is affected by visual malin, and later transferred to alcohol. Speci- cues associated with fin morphology in some mens were collected at less regular intervals species,which in turn can influence mating suc- during 1984 from Caiio Maporal, a broad shal- cess (Baerends and Baerends von Roon, 1950; low creek of the low llanos of Apure state (7~7'OO'N, 69°32'OO'W), and preserved in the Barlow, 1974; Baylis, 1974). Large, slow-moving cichlids with broad me- same manner. Additional collections were made dial fins are conspicuous and potentially vul- at each site during Jan. 1988 and 1989. Both nerable targets for fin-nipping piranhas. This Caiio Maraca and Caiio Maporal exhibit dra- report offers evidence that Astronotus ocellatus matic changes in response to seasonal rainfall and perhaps several other large neotropical (Winemiller, 1989a, 1989b). During the dry cichlids gain a measure of protection against fin season, there is little significant discharge, and predation via caudal mimicry of the head re- water at each site is confined to the main chan- gion. This head mimicry is achieved by three nel. Fish densities are highest at both sites dur- morphological features: 1) the caudal ocellus; ing the dry period (Oct.-April). Heavy rains 2) dense, opaque scalation of the medial fins; from May-Sept. cause extensive flooding of and 3) symmetry of the lateral profile. The cau- broad, low-lying floodplains. Aquatic macro- dal ocellus, or eyespot, of A. ocellatusconsists of phyte and periphyton production is high and a bright orange ring of scales surrounding a many fishes spawn during this period. Caiio black spot at the dorsolateral base of the caudal Maraca has four piranha species:Pygocentrus no- fin. Except for the conspicuous ocellus and or- taus, S. irritans, S. medini, and S. rhombeus(Wine- ange iris of the eyes, the coloration of A. ocellatus miller, 1987, 1989b; see below). Caiio Maporal is drab and cryptic. Depending on the fish's be- has at least eight piranha species:Catoprion men- havioral state and environment, body color- to, Pristobrycon sp;, S. altuvei, S. elongatus, plus ation can quickly change from uniform grey to the four species at Maraca (Nico and Taphorn, a mottled pattern consisting of dark grey and 1988). Specimens were deposited in the TNHC light brown to grey patches. Less than half of and MCNG (institutional abbreviations are as 1% of wild A. ocellatusexhibit two or more ocel- listed in Leviton et al., 1985). li, usually near the base of the dorsal fin or sides of the body (Winemiller, pers. obs., n > 250 Measurements.- Diets of all fish speciescollected over 5 yr period in Venezuelan llanos). These at Callo Maraca were quantified by volumetric multiple ocelli are usually incomplete (some- stomach-contents analysis. Fish prey were iden- times consisting of only a black spot without the tified to species whenever possible. Identifica- orange ring) and apparently anomolous. Except tions were performed using a dissecting micro- for the brilliant caudal ocellus, wild A. ocellatus scope. Fishes were measured (all reported from the Venezuelan llanos are very drab com- lengths are SL) and fins were examined for re- pared with selectively bred color varieties re- cent piranha nips. Fins damaged by narrow- ferred to as "oscars" in the international aquar- bodied serrasalmin piranhas show distinct char- ium trade. Here I argue that most vertebrates acteristics. First, the distal fin margin within the probably perceive the caudal ocellus as an eye, damage area is usually crescent or rectangular much in the manner suggested for the ocellus in shape. Fins damaged by larger red-belly p.ira- of the eel-mimicking coral reef fish CalloPlesiops nhas, Pygocentrusnotatus, are much broader in altivelis (McCosker, 1977), marine butterfly fish- relation to the depth of the nip than fins nipped es, Chaetodonspp. (Cott, 1957), and eyespots on by Serrasalmusspp. Nips from large P. notatus the wings of certain moths and butterflies (Blest, were extremely rare compared to Serrasalmus 1957). nips. Presumably, large P: notatus nips result WINEMILLER-CICHLID CAUDAL EYESPOT RR7 Fig. 1. Caquetia kraussii (left; 170-180 mm) and Astronotusocellatus (right; 170-210 mm) collected on the same date from the same habitat in the Venezuelan llanos. Extensive damage from fin-nipping piranhas is evident on C. kraussii, whereas A. ocellatussuffered only minimal damage to its dorsal and anal fins. Interspecific differences in patterns of caudal ocelli are apparent even in preserved museum specimens. from failed attempts at tearing out pieces of transparent and frequently exhibits abrupt dis- flesh rather than fins alone. However, some evi- continuity with previous soft-ray formations. dence suggests that juvenile P. notatus may at- Fins damaged by other agents, such as intra- tack fins rather than flesh (Machado-Allison and specific aggressive encounters among cichlids Garcia, 1986; Nico and Taphorn, 1988). Some or failed attacks by grasping predators show specimens captured by hook and line were dam- ragged borders rather than smooth edges. aged by P. notatusbefore they could be removed Recent fin nips were counted on all fins of A. from the water (evident from large bleeding ocellatus and Caquetia kraussii, another large wounds). cichlid found at Cano Maraca. Both specieshave Second, Serrasalmus spp. produce clean, a caudal ocellus, but that of A. ocellatus is far abrupt tears at the edge of damaged fins. Aquar- more symmetrical and brightly contrasting with ium observations revealed that three species (S. the fish's background coloration than that ofC. irritans, S. medini, and S. rhombeus)can instantly kraussii (Fig. 1). Specimens smaller than 40.0 clip off pieces of fin tissue with their razor sharp mm were not included in the analysis.Astronotus teeth. Tight occlusion of the teeth apparently ocellatus is widespread throughout lowland facilitates abrupt tearing of fins (some juvenile aquatic habitats of the Orinoco and Amazon Serrasalmusused a jerking motion to dislodge drainage basins. As a result it usually coexists fin fragments). sympatrically with several fin-nipping Serrasal- Regenerating fins retain unambiguous visible mus spp. evidence of the initial extent of fin damage. Caquetiakraussii ranges from the Lake Mara- Newly rejzenerated fin tissue is usually more caibo and coastal drainag:es of Venezuela into 668 COPEIA, 1990, NO.3 undamaged distal tissue on either side of the .c I/) nip. Nips were not measured if bordered by ii: other recently damaged or partially regener- Q; ated tissue. Nips located on the edge of rect- ll- angular fin margins were not measured when l/) Co undamaged distal tissue only remained on one Z side of the nip. Fin nips were also measured on Q) 01 preserved specimens of Crenicichla saxatilis LU Q; (Cichlidae) from Callo Maraca and Cichla ocel- > ct laris (Cichlidae) collected from Callo Maporal. Fin nips were classified as either narrow (depth of nip greater than width), broad (nip width greater than depth), or intermediate (nip depth and width roughly equal, resulting in a semi- circular notch). Based on piranha jaw shapes, broad nips were assumed to correspond to at- tacks by P.