Reproductive Ecology ofthe Gobiid Fish Eviota abax at Nobeoka, Japan, with Notes on Geographic Variation! Masanori Taru2 and Tomoki Sunobe 3 Abstract: The reproductive behavior and spawning cycle of the gobiid fish Eviota abax were observed in a rocky tide pool at Nobeoka, Miyazaki, Japan. Both sexes maintained nonterritorial, overlapping home ranges. The spawnings took place at the low tide ofneap to spring tidal periods. Matings varied in each spawning cycle, but males did not simultaneously mate with multiple females. Males were larger than females in the spawning pairs. After spawning, only the male guarded the egg mass. Although separated by 900 km, the basic patterns of reproductive ecology were similar at Nobeoka to those reported earlier for this specie,s from Kominato, Chiba, Japan; nest entrances were smaller at Nobeoka than at Kominato, and larger males kept their home ranges longer at Nobeoka. INTRASPECIFIC GEOGRAPHICAL variation in In this paper we describe the spawning behavior has been the focus of recent re­ cycle, mating system, and egg-guarding be­ search on the mechanism of evolution of be­ havior of the gobiid fish Eviota abax at No­ havior brought about by environmental beoka, Miyazaki, Japan, and compare it with variation (Foster and Endler 1999). Such be­ the reproductive ecology of another popula­ havioral variation could result in reproductive tion 900 km distant at Kominato, Chiba, Ja­ isolation of individuals from different hab­ pan, previously studied by Tarn and Sunobe itats. Therefore, it is important to discuss (2000). conspecific behavioral variation among pop­ Eviota abax is a small species «50 mm to­ ulations from different habitats to elucidate tal length), inhabiting shallow subtidal and possible evolutional sequences of specializa­ lower intertidal rocky shores and coral reefs tion (Verrell 1999). in southern Japan (Lachner and Karnella However, comparative studies on geo­ 1980). The spawning season is from May to graphic variation of behavior among reef August in Kyushu (Dotsu et al. 1965). Larvae fishes whose larvae disperse by water currents have been collected from June to October, and settle out in different habitats following but are particularly abundant from July to metamorphosis are rare. Yanagisawa (1982) August at Kominato (Okabe 1998). Sunobe investigated the reproductive ecology of the (1998) described courtship behavior of E. gobiid fish Amblyeleotris japonica from two abax in an aquarium. The female lays an egg different populations; Akagawa and Okiyama mass on the wall of the nest, and the male (1997) examined the reproductive and feeding guards the embryos for approximately 5 days behavior of the file fish Rudarius ercodes from at 22-28°C until hatching (Dotsu et al. 1965, four populations. Sunobe and Nakazono 1987). METHOD~ 1 Manuscript accepted 14 May 2001. MATERIALS AND 2 Marine Biology Laboratory, Faculty of Science, Toho University, 2-2-1, Miyama, Funabashi-shi, 274­ This study was carried out on the rocky shore 8510, Japan (E-mail: [email protected]). in front of the Fisheries Research Laboratory 3 Natural History Museum and Institute, Chiba, 955­ of Miyazaki University, located on the east 2 Aoba-cho, Chuo-leu, Chiba-shi, 260-8682, Japan. coast of Kyushu Island (32° 31' N, 131° 42' E). We observed the behavior of Eviota abax Pacific Science (2002), vol. 56, no. 1:35-40 by snorkeling one to three times a day be­ © 2002 by University of Hawai'i Press. tween 0530 and 1900 hours from 7June to 31 All rights reserved August 1997, except for stormy days. Ob- 35 36 PACIFIC SCIENCE· January 2002 servations 'were made on 67 days for a total of RESULTS approximately 169 hr. The water temperature varied from 21.3 to 28.7°C during the obser­ Thirty-four males (mean, 27.8 mm SL ± 4.52 vation period. SD; range, 19.1-37.6 mm) and 50 females A quadrat (1.8 by 5.8 m) divided into 213 (mean, 27.1 mm SL ± 3.14 SD; range, 20.9­ 20 by 20 cm grid squares was set on a rock 35.5 mm) were seen during the observation face and cobble field at 0-1.5 m depth inside period. The mean operational sex ratio (OSR) a tide pool. Before the beginning of ob­ was male: female = 1 : 0.98 and fluctuated servations, from 23 May to 6 June, we cap­ between 1 : 0.2 and 1 : 3. The mean period of tured all individuals of E. abax in the obser­ time that fish remained at the observation vation area with a hand net. They were area was 42.0 days (range, 1-88 days ± 28.3 individually discriminated by the color pat­ SD) for males and 45.8 days (1-89 days ± tern on the nape and by clipping ofthe upper 26.3 SD) for females. or lower part of the caudal fin. Standard Figure 1 shows the arrangement of the length (SL) and total length (TL) were mea­ finalized home range boundaries between 28 sured and sex was determined by the degree July and 3 August, when observed reproduc­ of elongation of the first two dorsal spines tive behavior was most frequent. Neither sex (which are elongated by 150-200% in males) exhibited any territorial behavior; instead, and the shape of the urogenital papilla home ranges of all individuals exhibited con­ (Lachner and Karnella 1980). Previously un­ siderable overlap with each other. Feeding encountered individuals appearing after the occurred within the home ranges. Among start ofobservations on 7June were cataloged males, larger individuals retained their home in the same manner. The total number of ranges longer than smaller males (Kendall's identified males and females was 34 and 50, rank correlation test, Z = 2.18, P = 0.0293 < respectively. 0.05, Figure 2). Five instances of male-male We recorded the swimming tracks for each aggressive interactions associated with ob­ individual for 5 min on each sample day. taining spawning nests were observed during Tracks ofmale courtship and female response the study period. Aggressive behavior oc­ were excluded from data used to determine curred in the following sequence: males fac­ their home ranges. Subsequently, we esti­ ing each other at 1 to 5 cm, head up with mated the size and boundaries of individual open mouth, lateral display while circling home ranges by combining swimming track each other with expanded dorsal and caudal data for each individual fish. We noted the fins, darting at adversary male and biting its degree of abdominal swelling in the females body. In all five cases, the larger male drove each sample day and assumed that the female the smaller male away from its periphery, had spawned on the same day if the swollen thus winning the aggressive interaction. The abdomen became substantially reduced. We males used small holes, rock cracks, or empty then analyzed the possible relationships shells of the oyster Crassotrea gigas as a among frequency of spawning, the lunar spawning nest. The shortest dimension of phase, and the tidal condition, using a tide measured nest hole entrances ranged from 7 table for Hososhima, Miyazaki, Japan (Japan to 20 mm (mean, 11.5 mm ± 4 SD; n = 12), Meteorological Agency 1996). When repro­ with nest hole depth ranging from 35 to 140 ductive behavior was observed, the time and mm (mean, 64.5 mm ± 30 SD). code number of the participants were re­ The number of spawning events observed corded. When the male guarded the egg mass, varied as cyclic ups and downs, when tidal we also recorded any animal species that the fluctuation was smaller and larger, respec­ male attacked. After hatching, we measured tively. Five spawning cycles were recognized directly the shortest dimension of the nest during the observation period (Figure 3). entrance that limited access and estimated the Reproductive behavior was initiated by depth of nest holes by inserting an aluminum a male visiting a female's home range. The wire and subsequently measuring it. male approached the female and exhibited Reproductive Ecology of Eviota abax . Taru and Sunobe 37 20cm FIGURE 1. Home ranges of all individuals appearing at the study site between 28 July and 3 August. Thick solid, Ihick broken, and thin solid lines indicate the finalized home range boundaries of egg-guarding males, non-egg-guarding males, and females, respectively. Solid circles show the locations of the males' nests. 90 . .. 80 courtship displays as described by Sunobe ....... lJ) (1998). The female responded to the male's >, 70 displays by following the male to his nest. 8'" After the male entered the nest, the female c:: 60 . 0 , "+:> . stopped at the entrance. As the male courted c:: ...Q) 50 from the entrance, the female entered the cr::Q) nest. Q) 40 Clc:: Eleven males participated in 18 spawning cr::'" 30 events: five males mated only once; five other Q) E males mated twice; and one male mated three 0 20 :I: .. times with different females in successive 10 spawning events. Females spawned once in any given spawning cycle and spawned one 0 to four times during the total observation 15 20 25 30 35 40 period. As a group, males were significantly SL (mm) larger than females in the mating pairs FIGURE 2. Relationship between male body size (standard (Wilcoxon's signed rank test, T = 15, Z = length [SL]) and retention of home range by males. -3.070, P = 0.0021, n = 18, Figure 4). 38 PACIFIC SCIENCE· January 2002 LunarPhase • o o o 200 • • • c:: e 150 ',p ro :::l +-'u lOa :::l \i:: ro "'0 50 i= lOa '" ,....... ~ 80 --(/) ~ ro E Q) \I- 60 "'0 Q) I- :::l P""-"1 +-'ro ~ ~ E 40 \l-e >. u • c:: Q) V 1\ :::l C'" Q) 20 I- U.