Shoaling and Factors Underlying Shoal Composition in Fish Chantima Piyapong 1

ว.วิทย. มข. 40(4) 1002-1012 (2555) KKU Sci. J. 40(4) 1002-1012 (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 group-living 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, Group-living of animals, Fish 1Department of Biology, Faculty of Science, Burapha University, Chonburi, 20131, Thailand E-mail: [email protected] บทความ วารสารวิทยาศาสตร มข. ปที่ 40 ฉบับที่ 4 1003 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 trade-offs 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 anti-predator 1004 KKU Science Journal Volume 40 Number 4 Review protection, foraging and reduced cost of groups, differing only in size (Krause and locomotion. The anti-predator 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 mono-coloured shoals whereas in hunting success decreases with increasing mixed-coloured 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 three-spine sticklebacks behaviour in terms of reduced costs of (Gasterosteus aculeatus ). Individuals prefer locomotion are the hydrodynamic advantages smaller shoals after they were food-deprived of swimming in a group. It was found that, due (Krause 1993). Similarly, it was found that to utilisation of vortices, there were reduced food-deprived killifish ( Fundulus diaphanous ) tail-beat frequencies and thereby energy spent more time alone and less time shoaling saving accruing to individuals in groups as than non-deprived 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

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