Blackwell Science, LtdOxford, UK FISFisheries Science0919-92682003 Blackwell Science Asia Pty Ltd 691February 2003 591 Behavior of domesticated 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 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 - 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.

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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. After the observation, fish were removed and their fork lengths and body masses were measured to the nearest 0.1 cm and 0.1 g, respectively.

Experiment 2: Latency to feed under chemical alarm signals

In this experiment, the feeding delay of individu- ally housed fish of domesticated, sea-ranched and wild origins after exposure to the chemical alarm signals was examined to estimate the ability of predator avoidance for each strain. As the alarm substance, a mixture of masu salmon body homo- genate and water from a recirculating tank con- taining piscivorous predators (Japanese Hucho perryi fed on juvenile masu salmon24) was Fig. 1 Schematic drawing of the tank used to measure served. Previous studies have shown that juvenile feeding latency after exposure to chemical alarm signals. fish react negatively to such an odor.25,26 Seven masu salmon from the three strains (about 50 g total) were homogenized in a blender and mixed the feeding location. Then, 100 mL well water with- with 950 mL of water from the huchen tank. This out odour was added to the inflow pipe. After stock solution was stored in 50 mL portions at - 1 min, further pellets were dropped at 15 s inter- 30∞C until about 1 h before use. Before use as pred- vals until the first piece was intercepted by the fish. ator water, the stock solution was diluted 400¥ to a This latency to accept food served as the control concentration found suitable for the experiment value. Ten to 20 min after the control measure- by preliminary experimentation. ment, 100 mL water with alarm substance was The fish were tested in 50 ¥ 40 ¥ 16 cm sections added to the tanks. After 1 min, we dropped from of rectangular flume tanks, which also provided one to eight pellets at 15 s intervals until the first overhead cover for the fish (Fig. 1). The bottom of piece was eaten. If fish did not respond to the the tank was covered with gravel (0.5–2.0 cm in dropped food, we continued providing pellets at diameter). Black plastic sheets around the tank lengthening intervals (1, 2, 4, 7 and 10 min) to a created a blind to prevent unintentional distur- maximum of 13 pieces (26 min after odor introduc- bance of the fish and observations were made tion) at which time the trial was terminated. We through a hole in the blind. Well water of 13∞C was estimated the willingness of each fish to feed in the supplied at a rate of about 1 L/min. Food pellets presence of predator cue as the differences in were supplied through a hose and sank through the response to food between control and alarm water. water column to a net-covered drain area if not After a trial, the fish was removed, anesthetized, intercepted by the fish. Water was introduced and its fork length and body mass recorded to the through a perforated plastic tube, generating a cur- nearest 0.1 cm and 0.1 g, respectively. Fish that did rent against which the fish held station. not respond to food input in presence of control For the experiment, a fish was chosen randomly water were excluded from the experiment. from one of the strains and placed in one of 12 tanks. In 111 tested fish from three strains, the mean fork length did not significantly differ (Wild, Statistical analysis 6.76 ± 0.63 cm, n = 40; Sea-ranched, 6.89 ± 0.37 cm, n = 28; Farmed, 6.94 ± 0.58 cm, n = 43; ANOVA, Frequencies of aggression and feeding movements F2,108 = 1.13, P = 0.33). After an acclimation period were square-root transformed to standardize vari- of at least 20 h, pellets were given until a fish had ances and improve normality. One-way analyses of eaten three pieces and was deemed familiar with variance (ANOVA) were used to examine differences

Behavior of domesticated salmon FISHERIES SCIENCE 91

of these variables among the three strains. For the observation. The frequency of the dominant’s comparisons of ANOVA means, Scheffé’s tests were agonistic behavior was not significantly different applied. The outcome of dominance contests were among the three strains tested (ANOVA, F2,84 = 0.41, analyzed by group (e.g. wild vs farmed) using chi- P = 0.67, Fig. 2). In dominance comparison, there squared tests. Expected number of wins were was no significant difference among the three calculated based on p (win) = 0.5. Unresolved con- strains (chi-squared test, Farmed vs Wild, c2 = 0.59; tests were divided equally between the two fish Sea-ranched vs Wild, c2 = 0.76; Farmed vs Sea- groups. Observations of feeding latency time in ranched, c2 = 0.03; all cases P > 0.05, Table 1). Experiment 2 were analyzed by Mann–Whitney Farmed fish showed a significantly higher number tests because of non-normal data structure. A of feeding bites per 5 min than the wild fish (ANOVA, probability value of 0.05 was used as a significance F2,84 = 6.41, P < 0.01, Scheffé’s tests; Farmed vs Wild, criterion in all tests. P < 0.01; Wild vs Sea-ranched, P = 0.10; Farmed vs Sea-ranched, P = 0.34, Fig. 2).

RESULTS Latency to feed under chemical alarm signals Dominance in pairwise encounters Almost all fish (109/111) showed a response to In 87 of 91 contests, the dominance score revealed olfactory cue immediately and sought refuge under a dominant individual; the remaining pairings cover. The time to re-emerge from cover and take were considered unresolved. The differences in the first food differed among strains. About 50% scores between dominant and subordinate fish of the farmed fish showed no difference in latency were, on average, 3.14. Regardless of fish strain, to feed between control and alarm water, whereas the dominant fish defended its position in the almost 50% of the wild fish did not re-emerge upstream by frequently approaching the subordi- by the 13th piece of food (Fig. 3). Those fish that nate fish and occasionally nipping, chasing or per- delayed feeding beyond the observation period forming lateral display. Almost all subordinate fish were pooled in a category ‘> 12’ for non-parametric stayed at the bottom or surface of the tank and comparison of latency among strains. For fish that never counterattacked the dominant fish during did come out to feed within the observation period, the average number of pellets (predator condi- tioned water minus control) for farmed, sea- ranched and wild strains were 4.5, 7.0 and 7.5 pieces, respectively. Avoidance behavior after the introduction of chemical alarm signals was sig- nificantly different between farmed and wild strains (Mann–Whitney test, Z = - 2.02, P < 0.05), but not between farmed and sea-ranched, or sea- ranched and wild strains (Farmed vs Sea-ranched, Z = - 1.26, P = 0.21; Sea-ranched vs Wild, Z = - 0.46, P = 0.64).

DISCUSSION

Studies comparing agonistic behavior between farmed and wild juvenile salmonids have yielded

Table 1 Results from the dominance experiment among the three strains of masu salmon Winner Combination n Fa Wi Se Unresolved Fa vs Wi 29 17 12 – 0 Se vs Wi 33 – 18 13 2 Fig. 2 Frequency of aggressive behavior and feeding Fa vs Se 29 14 – 13 2 movements (± SE) of dominant individuals in pairwise con- tests among farmed, sea-ranched and wild fish. **P < 0.01. Fa, Farmed; Se, Sea-ranched; Wi, Wild; –, no data. 92 FISHERIES SCIENCE T Yamamoto and UG Reinhardt

hatcheries depends on the amount of food given and distribution. To elucidate how hatchery selec- tion may lead to their aggression, it is necessary to compare fish husbandry techniques in domesti- cated stocks that do show increased aggression with those for stock that do not show greater aggression than the wild ancestor. We showed in experiment 2 that farmed fish were more active under apparent risk of predation than wild fish. In other salmonids, several workers have also investigated differences in antipredator behavior between wild and domesticated fish.13,17,31 The ultimate reason for the diminished predator avoidance behavior of farmed fish is the lack of predators in hatcheries or a combination of lack of predators plus selection for fast growth. It is likely that in our experiment the observed greater fre- quency of feeding movements (experiment 1) and the earlier resumption of feeding under threat (experiment 2) were both an expression of elevated motivation to feed and grow in the domesticated fish. Johnsson et al.14 showed the same effect of hatchery selection and growth-hormone injection on growth, feeding activity and antipredator avoid- ance in brown trout, Salmo trutta. The domesti- cated masu salmon in the present study had not lost their fright response to danger cues com- pletely, but their faster resumption of feeding Fig. 3 Relative frequency of three categories of feeding argues for a shift in the balance between the drives latency after introduction of chemical alarm signals in to forage and exercise caution. three strains of juvenile masu salmon. Categories are: , Our data show that aggressiveness and ability to £ 0 food pieces difference between control and predator avoid predators in the sea-ranched fish was inter- water; , 1–12 pieces differences; , > 12 pieces differ- mediate between wild and farmed fish. Waples15 ences. *, Denotes a significant difference at P < 0.05. argued that selection regimens for cultured and wild fish populations will inevitably differ, even when the hatchery environment represents only a portion (e.g. from egg to smolt) of the life cycle. Our contradicting results. As domesticated fish have result supports the notion that the duration of been bred selectively to attain increased growth, hatchery stay (in terms of proportion of life cycle these fish can be expected to be more aggressive, if or number of generations in captivity) determines there is a positive correlation between aggression the amount of deviation from the wild type. and access to food. Indeed, Einum and Fleming17 In the present study, we assumed that behav- provided evidence for that domes- ioral differences among the three strains are not ticated fish were more aggressive and conse- caused by origin- and sex-specific behavioral dif- quently grew faster than wild fish. In contrast, ferences. However, previous studies in salmonids Johnsson et al.27 found no difference in aggressive have shown that agonistic behaviors of juvenile behavior between wild and farmed juvenile brown salmon were different among rivers.32,33 Further- trout. The present study also showed that the fre- more, Johnsson et al.34 detected that male juveniles quency of aggressive behavior and relative domi- of brown trout attacked frequently more than nance did not differ among farmed, sea-ranched females, while males reacted less to predator attack and wild fish, while farmed fish showed greater than females. Therefore, the behavioral difference apparent feeding than wild fish. Recent work that we have documented cannot be fully demon- showed that an individual’s aggressiveness did not strated as the result of the effects of domestication correlate with growth rate when the fish were to behaviors. Further studies in behavioral charac- housed in holding tanks at high density.28,29 More- teristics among several populations and between over, Ruzzante30 suggested that the evolution sexes would be necessary to ascertain the effect of towards increased or decreased aggression in domestication to behaviors. Behavior of domesticated salmon FISHERIES SCIENCE 93

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