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Dominance and Predator Avoidance in Domesticated and Wild Masu Salmon Oncorhynchus Masou

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Dominance and Predator Avoidance in Domesticated and Wild Masu Salmon Oncorhynchus Masou Blackwell Science, LtdOxford, UK FISFisheries Science0919-92682003 Blackwell Science Asia Pty Ltd 691February 2003 591 Behavior of domesticated salmon T Yamamoto and UG Reinhardt 10.1046/j.0919-9268.2002.00591.x Original Article8894BEES SGML FISHERIES SCIENCE 2003; 69: 88–94 Dominance and predator avoidance in domesticated and wild masu salmon Oncorhynchus masou Toshiaki YAMAMOTO* AND Ulrich G REINHARDTa Laboratory of Conservation Biology, Field Science Center for Northern Biosphere, Hokkaido University, Sapporo, Hokkaido 060-0809, Japan ABSTRACT: Dominance, aggression and predator avoidance were compared among farmed, sea- ranched and wild juvenile masu salmon Oncorhynchus masou in laboratory experiments. Domesti- cated fish (farmed and sea-ranched), which had been exposed to artificial selection, were not dominant against wild fish in pairwise contests, nor did they show greater aggressiveness. Farmed fish did show greater feeding than wild fish. Under chemically simulated predation risk, farmed fish were more willing to leave cover and feed than wild fish, indicating reduced predator avoidance in the farmed fish. Our results indicate that selection for fast growth (domestication) in masu salmon favors fish that respond to food quickly and ignore predation risk. KEY WORDS: aggressive behavior, hatchery, masu salmon, predator avoidance. INTRODUCTION impacts the growth of individuals.9 In other salmo- nids, aggressiveness of domesticated juveniles has Numerous studies on salmonids have investigated been shown to increase.10 Therefore, introduced the differences in morphology, genetics and masu juveniles may influence wild populations behavior between domesticated and wild fish of directly through aggressive contests for territories. the same species.1–4 It has become clear that the As masu salmon show strong local adaptations,11,12 introduction of cultured fishes into rivers may there is concern that the introduction of domesti- have negative effects on wild fish populations. For cated fish may lower the viability of wild masu example, large numbers of domesticated Atlantic populations. Another concern is that artificially salmon Salmo salar L. have escaped from aquacul- enhanced masu juveniles may have low freshwater ture facilities and entered rivers to spawn.5 These survival due to reduced antipredator behavior.13,14 fish may then compete and eventually interbreed Thus, for the successful management of this and with wild fish, changing the genetic composition other enhanced salmonid species, an investigation of the stock6 and potentially disrupting local of behavioral differences between hatchery and adaptations.7 wild fish, and their underlying selection regimens, In recent years, large numbers of hatchery- is needed. reared juvenile masu salmon Oncorhynchus How much the behavior of domesticated fish masou, which is native to eastern Asia, have been diverges from their wild ancestors likely depends released as commercial and recreational fisheries on the intensity of artificial rearing.15 Fish may resources in Japan. However, very little is known complete the full life cycle in the hatchery (farmed about the interactions between these domesti- fish) or may be reared in a hatchery from the egg cated fish and wild salmon. Juveniles of wild masu to a juvenile stage to be then released into the wild salmon spend at least 1 year in the stream environ- (ranched fish). Other than studies on hybrids of ment before migrating to sea.8 In this period, they farmed and wild fish,16,17 little attention has been aggressively compete for feeding territories, which given to the question of how behavior of fish is affected by the degree of domestication. The purpose of the present study was to com- pare territorial dominance, aggressive behavior * Corresponding author: Tel: 81-11-706-2585. Fax: 81-11-706-2587. Email: [email protected] and predator avoidance among juvenile masu aPresent address: Department of Biology, Eastern Michigan salmon of wild, farmed and sea-ranched origins University, 316 Mark Jefferson, Ypsilanti, MI 48197, USA. in order to predict the outcome of interactions of Received 1 August 2001. Accepted 23 July 2002. such fish strains in the wild. Behavior of domesticated salmon FISHERIES SCIENCE 89 MATERIALS AND METHODS screens. Food pellets (0.15 g; 2% mean body weight per day) were dropped at the upstream end of each Experimental population compartment by automatic feeders. Therefore, fish that occupied a more upstream position obtained Farmed fish were reared at the Hokkaido Fish the most food. To determine the distance of a fish Hatchery in Mori, southern Hokkaido. The farmed relative to the feeder, a measuring tape was fixed to strain originated from the Chihase and Touhoro the side of the tank. rivers in 1965 and had been hatchery-reared for at A single fish was randomly chosen from each of least 30 years.18 These fish were developed for the two strains and one randomly assigned individual Japanese fish farming industry and have been bred was marked by clipping of the adipose fin. In 91 selectively to attain increased growth and early contests, mean fork length of three strains was not reproductive maturity. Sea-ranched fish, which are significantly different (Wild, 6.59 ± 0.57 cm, n = 62; reared in a hatchery environment from egg to the Sea-ranched, 6.57 ± 0.54 cm, n = 62; Farmed, age of 3-month-old juveniles, were obtained from 6.69 ± 0.55 cm, n = 58; ANOVA, F2,179 = 0.86, P > 0.05). the Hokkaido Salmon Hatchery in Shari, eastern The relative difference in body size between two Hokkaido. The Shari River (43∞50¢N, 144∞36¢E) is fish (A, B cm) that was chosen was calculated by approximately 54.5 km in length and 565.6 km2 in using |100 ¥ (A - B)/(A + B)|. Previous studies have catchment area. In this population, for at least the found that a larger size difference between fish last 30 years, fish have been released at the juvenile influenced the outcome of the social status.9,19 stage and the released fish that matured after 1 year Thus, we estimated the range where body size for fertilization were collected (Hokkaido Salmon had no effect in determining the dominance (T Resource Center, unpubl. data, 1968–1997). Fish of Yamamoto, unpubl. data, 1998) and used only the the Shari strain used in the experiments were the results of the contest between individuals that had offspring of parents that had been sea-ranched. a relative difference in body size of less than 2%. The third stock in the present study was wild fish After the fish were acclimated to the test tank from the Shakotan River, located in western Hok- (13∞C, LD 14 : 10) for 20 h (12.00–08.00 h), aggres- kaido (42∞21¢N, 141∞25¢E). The Shakotan River is a sive behavior and position of the two fish relative small river 15.4 km long with a 75.1 km2 catchment to the feeding location were observed for a period area. This river has been closed to fishing for about of 5 min, both of which correlated well with domi- 30 years due to fishing regulations, and domesti- nance.20 The preferred position was assumed to be cated masu salmon has not been released there in upstream of the other fish because this ensured recent years. The wild fish used in this experiment first access to the food. In this experiment, posi- were collected by electrofishing from the Shakotan tion relative to the food source and swimming River in 15 June 1998. style determined a dominant fish. Dominance Fish from each strain were transported to the points for each fish were recorded three times Tomakomai Experimental Forest Station in June during the 5 min observation period: at the start, 1998 and held in separate holding tanks under sim- 1 min and at the finish time. The tank was divided ilar conditions for approximately 1 month [12∞C, into four quarters from the upstream to the down- light : dark (LD) 14 : 10]. The fish were given a daily stream end. If at an observation time one fish was food ration (commercial trout pellets) equaling in a more upstream quarter than the other fish, 2% of their body weight. The following experi- it received one point, while the downstream fish ments were carried out from early August to late received zero points. If both fish occupied the September 1998. same quarter, no points were awarded. It has been observed for masu salmon that the loser has a tendency to remain in the corner of a tank in a Experiment 1: Dominance in pairwise pairwise contest.21 A fish swimming in the water encounters column at the observation time was awarded one point, whereas a fish staying within one body In order to determine relative dominance among depth of the surface or bottom received zero farmed, sea-ranched and wild individuals, pair- points. Thus, the highest possible dominance wise dominance tests were carried out in partly score for a fish in this experiment was 6. In each recirculating artificial stream tanks (280 ¥ 35 cm). pair, the fish having the higher sum of points at the Fish were kept in an 80-cm long compartment with end of the trial was considered dominant. Obser- a layer of gravel (0.5–2.0 cm in diameter) on the vations on 12 pairs at the end of the experiment bottom and water depth was maintained at 15 cm. showed that the dominance established after 1 day The tanks were surrounded by opaque screens and in the tank did not change over a period of an observations were made through a slit in the additional 2 days of observation. 90 FISHERIES SCIENCE T Yamamoto and UG Reinhardt For each fish in a pair, we also recorded the occurrence of aggressive interaction (including nip, approach, lateral display and chase following Jenkins22 and Brown and Brown23) and the number of feeding movements, defined here as orienting to particles in the water column and quick opening of the mouth, during the 5 min observation period.
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