ว.วิทย. มข. 40(4) 10021012 (2555) KKU Sci. J. 40(4) 10021012 (2012)

การอยูเปนฝูงและปจจัยที่มีผลตอองคประกอบของฝูงปลา Shoaling and Factors Underlying Shoal Composition in Fish Chantima Piyapong 1

บทคัดยอ บทความนี้ทบทวนเรื่องการอยูกันเปนกลุมในสัตวโดยเนนไปที่พฤติกรรมการอยูเปนฝูงในปลา ซึ่งให ภาพรวมโดยทั่วไปของความรูที่เกี่ยวกับพฤติกรรมการอยูเปนฝูง ขอเสียและขอดีในการอยูเปนฝูง ปจจัยที่อาจมีผล ตอองคประกอบของฝูงหรือมีอิทธิพลตอการตัดสินใจของปลาแตละตัวในการที่จะรวมฝูงใดฝูงหนึ่ง ซึ่งปจจัยเหลานี้ ไดแก ชนิด เพศ การแบงตามฟโนไทป ภาระทางปรสิต ความคุนเคยและความเปนเครือญาติ

ABSTRACT This article reviews groupliving of animals, by focusing on shoaling behaviour in fish. It provides a general overview of shoaling behaviour, costs and benefits of this behaviour, and also factors which may underlie shoal composition or influence the decision of an individual to join a shoal. These include species, sex, phenotypic assortment, parasite load, familiarity and kinship.

คําสําคัญ: พฤติกรรมการอยูเปนฝูง การอยูเปนฝูงในสัตว ปลา Keywords: Shoaling behavior, Groupliving of animals, Fish

1Department of Biology, Faculty of Science, Burapha University, Chonburi, 20131, Thailand Email: [email protected]

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Shoaling behaviour literature exists between shoaling and the Shoaling is a behaviour of fish in term schooling (Shaw, 1978; Pitcher, 1983; which they remain together through social Paxton, 1996; Griffiths and Magurran, 1999; attraction (Pitcher and Parrish, 1993). This Croft et al., 2003). The term ‘shoal’ is behaviour is widespread among fish species commonly used to refer to any social and it has been estimated that over 50% of aggregation of fish, whereas ‘school’ refers approximately 25,000 species of fish engage in more specifically to a polarised group of fish, shoaling at least at one point of development defined by synchronised swimming behaviour during their ontogeny and around 25% of fish (Pitcher, 1983; Smith, 1997). Also, ‘school’ is species shoal throughout all of their lives used to refer to a subcategory of ‘shoal’ (Shaw, 1978). Such groups range from small (Smith, 1997). Therefore, the term ‘shoal’ is aggregations of small groups of cyprinid fishes used as an inclusive term to define a in freshwater habitats to huge pelagic groups functional aggregation of fish that may or may of marine fishes such as cod, herring or tuna. not be polarized in order to be consistent Because of the existence of enormous shoals throughout this thesis. of marine fishes, shoaling contributes to the commercial importance of fisheries (Shaw, The costs and benefits of shoaling 1978; Parrish, 1999). Fish shoals have also behaviour attracted biologists, especially behavioural Shoaling behaviour involves both ecologists, because they are model systems costs and benefits to individuals, the most to investigate several aspects of social important of which are considered to be behaviour and organisation (Krause and related to foraging and the avoidance of Ruxton, 2002). Shoaling in freshwater fishes predation and are considered to arise as a has been studied more often than shoaling in result of tradeoffs made by individuals within marine species, probably because pelagic fish a group (Pitcher and Parrish, 1993). However, move fast and usually form vast groups. This there are other costs and benefits of shoaling makes direct observation difficult and the to be considered (Krause and Ruxton, 2002). capture of complete shoals impossible in the The followings are brief summaries some of wild. In contrast these constraints are reduced the advantages and disadvantages of shoaling. in freshwater fishes (Krause et al., 2000). There are many potential benefits of A definition of shoaling has been the shoaling as reviewed in Krause and Ruxton subject of some debate and confusion in the (2002). These benefits include antipredator

1004 KKU Science Journal Volume 40 Number 4 Review protection, foraging and reduced cost of groups, differing only in size (Krause and locomotion. The antipredator benefits Godin, 1995). Increased attack rate of include improved predator detection, attack predators on fish prey is also found because dilution, confusion and predator evasion. of the oddity effect. By using shoals of eight Consequently, individuals in shoals are safer minnows, Landeau and Terborgh (1986) than solitary fish. Even though predators discovered that bass capture success was very preferentially attack large shoals, predator low in monocoloured shoals whereas in hunting success decreases with increasing mixedcoloured shoals, the capture success of shoal size (Krause and Godin, 1995). Shoaling the bass increased dramatically when one also provides foraging benefits. Individuals colour type was in the minority and this type within a shoal are able to locate food more of minnow was caught by the bass at the swiftly than when solitary (Ranta and Juvonen, highest rate. This oddity effect also applies to 1993) and are able to gain access to defended body size and incurs costs to fish prey by resources (Foster, 1985). Additionally, shoaling increasing capture success of predators individuals are able to devote more time to (Theodorakis, 1989). Finally, there is a cost of foraging (Magurran and Pitcher, 1983), as they shoaling behaviour when foraging, because of reduce the time spent scanning for predators competition for resources. There is evidence (Caraco, 1979). Ancillary benefits to shoaling of competition among threespine sticklebacks behaviour in terms of reduced costs of (Gasterosteus aculeatus ). Individuals prefer locomotion are the hydrodynamic advantages smaller shoals after they were fooddeprived of swimming in a group. It was found that, due (Krause 1993). Similarly, it was found that to utilisation of vortices, there were reduced fooddeprived killifish ( Fundulus diaphanous ) tailbeat frequencies and thereby energy spent more time alone and less time shoaling saving accruing to individuals in groups as than nondeprived fish (Hensor et al., 2003). opposed to solitary individuals (Herskin and This suggests that state of hunger may affect Steffensen, 1998). the decision to join a shoal. When considering potential costs, larger groups are more apparent to predators Factors underlying shoal composition because of increased conspicuousness. There There are a number of factors which is evidence from laboratory experiments that may underlie shoal composition or influence fish predators showed a preference for larger the decision of an individual to join a shoal. groups when offered a choice between two These include species, sex, parasite load,

บทความ วารสารวิทยาศาสตร มข. ปที่ 40 ฉบับที่ 4 1005 familiarity and kinship which are described in Previous studies on Poeciliid fishes with more details below. polygamous mating systems have described Species (conspecific vs. that mate choice may determine association heterospecific) patterns. The sailfin molly (Poecilia latipinna ) A preference for conspecifics over showed that females prefer larger males over heterospecifics has been reported in a smaller males (Witte and Ryan, 1998). number of teleost species as reviewed in However, a later study found that the Krause et al. (2000). An early study on this preference for larger individuals in sailfin subject found that threespine sticklebacks mollies existed both within and between the showed a preference for conspecifics when sexes (Gabor, 1999). This finding suggests that the heterospecific stimulus fish were bitterling, natural selection for this species favoured the but not when roach were used (Keenleyside, observed association patterns not only for 1955). The functional significance of preferring mate choice but also for a variety of to group with conspecifics is likely to be due conditions such as predation pressures and to two main factors. By associating with shoaling behaviour. Sex composition of a conspecifics an individual reduces its chances shoal may influence shoal choice decision of suffering the increased predation risk of the when considering genetic relatedness of oddity effect. A similar case can be made for individuals in the shoal. In the rainbowfish foraging behaviour. The probability of (Melanotaenia eachamensis) it was found that detecting suitable food is likely to be females preferred to shoal with unrelated maximised in the company of conspecifics males rather than their own brothers. that have similar dietary preferences (Krause However, the females preferred to shoal with and Ruxton, 2002). However, fish showed no female relatives and only avoided male preference for conspecifics when considering relatives (Arnold, 2000). This study suggests the effects of familiarity. It was found that that females are able to discriminate male chub (Leuciscus cephalus ) demonstrated a relatives and show no preference to kin of the preference for familiar heterospecifics of opposite sex to avoid inbreeding. Recently, it minnows (Phoxinus phoxinus ) instead of non has been demonstrated that sex differences familiar conspecifics (Ward et al., 2003). may be a factor underlying shoal choice Sex decision in zebra fish ( Danio rerio ). By giving The sex composition of shoals may choices of shoals that differed in sex to focal influence shoal choice decisions both in terms fish, it was found that males preferred to of mating choice and shoaling behaviour. associate with female shoals over males

1006 KKU Science Journal Volume 40 Number 4 Review shoals, but no preference was found when a significantly more time with those that had a mixedsex shoal was presented as the black background. In the wild, there was alternative. However, females showed no evidence that freeranging shoals are assorted preference when given a choice between by body length as well (Krause et al., 1996; male and female shoals (Ruhl and McRobert, Hoare et al., 2000; Croft et al., 2003). These 2005). studies supported observed patterns of Phenotypic assortment laboratory studies that found a strong Association preferences for fish of preference for sizedmatched individuals. similar phenotype have been found in several Parasite load studies in the laboratory, especially Due to the confusion in the use of assortment for body length and colour as the terms of parasites and pathogens through reviewed in Krause et al. (2000). This can the literature, parasites are used throughout occur both when shoalmates are conspecific to refer to living organisms infecting fish both and when they are heterospecific. By internally and externally. These infectious associating with individuals with similar endoparasites and ectoparasites of fish phenotypes, fish may maximise their include viruses (Whittington et al., 1999), fungi individual fitness by minimizing the cost of (Ward et al., 2005), protozoa (Kolesnikova, both competitive asymmetries and oddity 1994) and worms (Krause and Godin, 1994; related predation risks (Ranta et al., 1994). In Barber and Huntingford, 1995; Blake et al., addition to the influence of the phenotypes 2006; Seppala et al., 2008; Tobler and of shoal mates on shoal choice decisions, the Schlupp, 2008). These parasites have been surrounding environment also has an effect shown to have an effect on shoaling (Bradner and McRobert, 2001). This study on behaviour and foraging ability as reviewed in assortment of body colouration in mollies Barber et al. (2000). Therefore, it is expected (Poecilia latipinna ) found that when black that species avoidance of parasitised individuals of mollies, were given the choice individuals has evolved, which may explain between two black shoals (i.e. consisting of the occurrence of parasiteassorted shoals in black individuals), one on a black background the field (Hoare et al., 2000). Parasitised fish and the other on a white one, more time was are found more often in peripheral shoal spent with the shoal on a black background, positions and show a reduced tendency for Similarly, when given the choice between two shoaling in some fish species (Barber et al., white shoals, blackcoloured fish spent 2000). Even though the risk of infection is an

บทความ วารสารวิทยาศาสตร มข. ปที่ 40 ฉบับที่ 4 1007 obvious cost of association, there might be a preference for familiar individuals may also tradeoff with a benefit such as foraging have important adaptive benefits. In an success. By capturing entire shoals of the experiment using fathead minnows banded killifish ( Fundulus diaphanus ) in the (Pimephales promelas ), it was found that in wild with an ingenious technique using a grid response to a predation threat from northern net that maintained the positions of pike ( Esox lucius ), the rate of predator individuals within shoals, it was found that inspections and the numbers of inspectors per individuals in the front section of a shoal inspection was greater in shoals consisting of tended to be not only larger than those in the familiar individuals in comparison to unfamiliar rear section, but also parasitised by the ones and the minnows in groups that were digenean trematode ( Crassiphiala familiar showed greater shoal cohesion than in bulboglossa ). In addition, parasitized fish were unfamiliar groups (Chivers et al., 1995). An also found more in peripheral positions than increase in shoal cohesion may not only result central ones in a significant number of shoals in increased antipredator success but foraging (Ward et al., 2002). In the binary choice test in benefits may also exist for associating with the laboratory in the same species, it was familiar individuals (Swaney et al., 2001). found that the relative shoaling preference of Furthermore, it may be of benefit for unparasitized individuals for unparasitized individuals to know the competitive ability of shoals increased with increasing degree of others and this may reduce levels of parasite load in parasitized stimulus fish. This aggression. Metcalfe and Thomson (1995) finding may imply that parasitised shoalmates showed that European minnows (Phoxinus may attract predators because of an oddity phoxinus ) could discriminate between shoals effect or may generally be of low quality in of poor competitors (with prior experience) terms of shared antipredator benefits such as and shoals with good competitors (without predator detection (Krause and Godin, 1994). prior experience) by preferring to shoal with Familiarity fish of low competitive ability. In an Several studies have demonstrated investigation of levels of aggression on that fish are capable of individual recognition. juvenile sticklebacks, UtnePalm and Hart Therefore, shoaling decisions may be based (2000) found that pairs of individuals that were on previous experience with other members familiar showed lower levels of aggression of the shoal and several studies have reported when sharing a common food source in shoaling preferences for familiar fish (see comparison to pairs of nonfamiliar individuals. review in Krause et al. (2000)). Shoaling Kinship

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Benefits of associating with kin may in kinstructured groups (Olsen et al., 2004). It include increased inclusive fitness among can therefore be seen that there is reliable shoalmates (Pitcher and Parrish, 1993; Ward evidence for kin recognition or kin preference and Hart, 2003). Decisionmaking to shoal with both in the laboratory and in semifield kin may be important in the evolution of co conditions. However, difficulties exist in operative behaviour (Dugatkin, 1997). There is detecting kinship in the wild because it is the evidence of kin recognition in a number of essential to capture an entire shoal to come fish species (Arnold, 2000; Hiscock and Brown, to firm statistically testable conclusions, and 2000; Frommen and Bakker, 2004; Frommen to use highly informative genetic markers et al., 2007; Hain and Neff, 2007). However, if (Krause et al., 2000). Furthermore, to analyse all test fish were reared in kin groups, these the data with the appropriate statistics to results may be due to preference for familiar detect kinship is of crucial importance (Luikart odours rather than an innate kin recognition and England, 1999). Taking into account these mechanism (Krause et al., 2000). Investigations three problems in the past, it is difficult to on guppies revealed that familiarity took find kin assortment in fish shoals in the wild; approximately 12 days to develop (Griffiths however, Piyapong et al. (2011) shows this and Magurran, 1997). Hain and Neff (2007) existence in the wild guppies. separated the juvenile guppies within 24 hours In conclusion, studying shoaling of birth. Consequently, the finding of kin behaviour and factors underlying shoaling recognition in guppies in this study should not composition may have important implications have been outweighed by familiarity. for understanding population viability, gene Investigation of kin recognition of fish has flow, and the management of and protection mainly focused on salmonids using young fish of commercially important, domesticated and and previous studies have shown that endangered fish species. For example, by salmonids are able to recognise kin (Olsen et removing potential predators from an al., 2004). Combining rearing experiments in ecosystem, it will not only have an effect on the laboratory and the advanced tagging of shoaling behaviour, but also the genetic fish in the wild, using passive integrated structure of the prey groups. transponders (PITs), it was found that siblings References swim spatially closer than unrelated fish Arnold, K. E. (2000). Kin recognition in rainbowfish during their seaward migration as smolts, (Melanotaenia eachamensis ): sex, sibs and supporting the hypothesis that smolts migrate shoaling. Behavioral Ecology and Sociobiology 48: 385391.

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