Observations of Agonistic Behavior between Two Island Kelpfish, Alloclinus holderi (Lauderbach, 1907) (Labrisomidae), at Anacapa Island, California.

Abstract

We describe a previously unreported agonistic behavior between two Alloclinus holderi (Lauderbach, 1907). Alloclinus holderi (family Labrisomidae) is a small, reef-dwelling fish reaching 15 cm total length (Love and Passarelli 2020). The species ranges from San Miguel Island, southern California to Isla Asuncion (27°06’N, 114°18’W), southern Baja California (Love and Passarelli 2020), Rocas Alijos (24°57.5’N, 115°45’W) (SIO 70-371), and into the Gulf of California at least as far northward as Playa Caleritas (24°21’N, 110°17’W) (González-Acosta et al. 2018), at depths between the intertidal and 91 m (Love and Passarelli 2020). The senior author observed and documented on video agonistic behavior between two fishes living on a rocky reef located at the south end of Cat Rock, Anacapa Island (34°00’12.5“N, 119°25’21.5”W) on the morning of 16 November 2019, at a depth of 12 m. Six to 10 A. holderi were observed within a crevice; most of these individuals were isolated from one another at an average distance of 0.5 m. In contrast, two individuals, of approximately equal size, were very close together, where they displayed a series of repetitious behaviors consisting of rising and lowering the front of the body while mouth gaping (Fig. 1). This was followed by biting, primarily of the opponent’s upper jaw (Fig. 2), although other head regions were sometimes involved. Jaw locking lasted between 3–63 secs and averaged about 20 secs. Most of the biting initiations were instigated by one individual (i.e., the one on the viewers’ right in Fig. 1). The senior author observed these interactions for about 3 min. At this point, the two fish engaged in a relatively long clasp during which time the gill operculae of both individuals began to open and close more rapidly than previously 63 secs after the initiation of this clasp, the individual on the right broke off and swam away. While this behavior has not previously been reported in this species, it is known from closely related taxa (i.e., both threat and attack behavior were described in Chaenopsis ocellata Poey 1865; Robins et al. 1959). In the Gulf of California both Paraclinus sini and Malacoctenus hubbsi defend territories through various forms of threat displays (Thomson et al. 2000) and shelter defense is common among the closely allied Chaenopsidae (Robins et al 1959; Thresher 1997; Hastings 2002) and Blenniidae (e.g., Losey 1968). Jaw locking seems particularly widespread, as it has been observed among the Labrisomidae (i.e., Labrisomus cricota; Sazima et al. 2002) and Chaenopsidae (i.e., Acanthemblemaria crockeri and Emblemaria hypacanthus; Thomson et al. 2000). In addition, the head raising behavior we observed has also been documented in some related taxa (e.g., “rearing up” in the Trypterygiidae, Wirtz 1978; “raised heads” in the labrisomid Dialommus fuscus, Nieder 2001). Territoriality among the Blennioidei often (although not always, Losey 1968)