Neotropical Ichthyology, 17(2): e180159, 2019 Journal homepage: www.scielo.br/ni DOI: 10.1590/1982-0224-20180159 Published online: 27 June 2019 (ISSN 1982-0224) Copyright © 2019 Sociedade Brasileira de Ictiologia Printed: 30 June 2019 (ISSN 1679-6225) Original article Unusual effect of chemical communication on social aggression in juvenile cichlid fish Cichlasoma paranaense (Cichliformes: Cichlidae) Ana Carolina dos Santos Gauy1,2, Marcela Cesar Bolognesi1,2 and Eliane Gonçalves-de-Freitas1,2 Some fish species are socially organized and show a social rank order which is achieved through aggressive interactions. After hierarchy is settled, such species communicate their ranks through several sensorial cues; this communication is adaptive because it reduces detrimental effects from physical contests. Cichlid fish are socially organized and signal their social ranks through visual, acoustic and chemical communication. The response to signaling may vary according to the species and environment; the knowledge of different species is fundamental to understand the evolutionary forces upon their social communication. We tested the effect of chemical signaling on social groups of juvenile cichlid Cichlasoma paranaense by renewing the water in the aquarium, a procedure that washes away chemical information and increases aggressive interactions in other cichlid species. Two treatments were designed: 50% and 0% water renewal. Aggressive interactions were video-recorded immediately before water renewal, 1min, 1h, 2h, and 24h after water renewal. The treatment with the water renewal did not increase aggressive interactions within the group. The 50% water renewal apparently reduced aggressive interactions in this species, indicating an interspecific difference on the aggressive response to chemical variation in the social environment. Keywords: Agonistic behavior, Social behavior, Social environment, Social signals, Water renewal. Algumas espécies de peixes são organizadas socialmente e apresentam uma ordem de rank social que é alcançada por meio de interações agressivas. Após o estabelecimento da hierarquia, essas espécies comunicam seu rank por diversas pistas sensoriais, essa comunicação é adaptativa, pois reduz os efeitos prejudiciais das lutas físicas. Peixes ciclídeos são socialmente organizados e sinalizam o rank social por comunicação visual, acústica e química. A resposta à sinalização pode variar de acordo com a espécie e o ambiente; o conhecimento sobre diferentes espécies é necessário para entender as forças evolutivas sobre sua comunicação social. Nós testamos o efeito da sinalização química em grupos sociais de juvenis do ciclídeo Cichlasoma paranaense por meio da renovação de água do aquário, um procedimento que dilui informações químicas e aumenta a interação agressiva em outras espécies de ciclídeos. Dois tratamentos foram realizados: 50% e 0% de renovação da água. A interação agressiva foi registrada imediatamente antes da renovação da água, 1min, 1h, 2h e 24h após a renovação da água. O tratamento com renovação não aumenta as interações agressivas dentro do grupo. A renovação de 50% da água do aquário aparentemente diminui as interações agressivas nessa espécie, indicando uma diferença interespecífica na resposta agressiva a variação química no ambiente social. Palavras-chave: Ambiente social, Comportamento agonístico, Comportamento social, Renovação de água, Sinais sociais. Introduction chemical communication is used in several social contexts (Keller-Costa et al., 2015), such as reproduction (see Social communication in fish occurs through several Giaquinto et al., 2010; Huertas et al., 2014), alarm (see sensorial modalities, such as visual, acoustic and chemical; Barreto et al., 2010, 2013), recognition of conspecific, both the latter is remarkably widespread in their communication among adults (see Plenderleith et al., 2005; Thünken et (Sorensen, Stacey, 2004; Huertas et al., 2008). In cichlid al., 2009), and among young-adults, influencing parental fish, a group of species with a rich behavioral repertoire, care (see Wisenden, Dye, 2009; Wisenden et al., 2014). 1Laboratório de Comportamento Animal, Departamento de Zoologia e Botânica, Universidade Estadual Paulista Júlio de Mesquita Filho (UNESP), Rua Cristóvão Colombo, 2265, 15054-000 São José do Rio Preto, SP, Brazil. (ACSG) [email protected], https://orcid. org/0000-0001-8150-1293, (corresponding author) 2 Centro de Aquicultura da Universidade Estadual Paulista Júlio de Mesquita Filho (UNESP) - CAUNESP, Brazil. (MCB) marcelacbolognesi@ gmail.com, https://orcid.org/0000-0002-0643-5297; (EGF) [email protected], https://orcid.org/0000-0003-1896-3035. e180159[1] Neotropical Ichthyology, 17(2): e180159, 2019 2 Chemical communication and aggression in Cichlasoma paranaense The use of chemical signals to show social rank, either signaling in juvenile C. paranaense social groups by as dominant or subordinate individuals, has been studied renewing the water in aquarium, a procedure that washes mainly in African cichlids, including, Oreochromis away chemical information and increases aggressive mossambicus (Peters, 1852), Oreochromis niloticus interactions in other cichlid species. The family Cichlidae (Linnaeus, 1758) and Astatotilapia burtoni (Günther, consists of diverse group of species varying in colors, 1894). Barata et al. (2007) showed that Mozambique behaviors and niches, which probably reflects a variety tilapia males (O. mossambicus) store urine and use it to in chemical communication mechanisms (Keller-Costa et signal their dominant position. This behavior modulates al., 2015). Comparing species within this group can be a aggressiveness in rival males, contributing to the stability way to provide more comprehensive information on their of the social hierarchy. According to Giaquinto, Volpato evolutionary forces driving social behavior. (1997), the absence of chemical signals prevents or delays the establishment of social hierarchy in juvenile Nile Material and Methods tilapia (O. niloticus). Additionally, renewing the water in aquaria increases aggressive interactions because it dilutes Fish housing. Fish were collected from water bodies chemical signals used for social rank recognition thus in the city of Frutal, MG, Brazil (20°03’37.40” S and disturbing the hierarchy stability in juvenile Nile tilapia 49°12’16.09” W), and acclimated in the lab for 20 days in (Gonçalves-de-Freitas et al., 2008). Maruska, Fernald 500-L polypropylene tanks (ca. 1 fish / 10L) with water at (2012) demonstrated that dominant A. burtoni males 27 ± 1ºC and a 12 h light/dark light regime (from 07:00 to increase the frequency of urine releasing in the presence of 19:00 h). Fish were fed with commercial food (Fri-Ribe® another male, thus showing that chemical signals are used Tropical Fish, 28% crude protein) twice a day (8:00 a.m. to inform the individual’s dominance status. Altogether, and 6:00 p.m.) to apparent satiation. Water quality was these studies have shown that chemical communication is maintained through Canister biological filters (filtering 400 adaptive because it signals social rank, thus reducing the L / h) and constant aeration. detrimental effects of physical contests. There was not evident external sexual dimorphism in C. The ecology and evolution of African cichlids have paranaense. Juvenile fish were used to avoid the effect of been well documented. However, little is known about sex on aggressive interactions, since cichlid males appear this mechanism on social rank signaling in Neotropical to show higher androgen levels than females in adult life cichlids. Some differences in social signaling among them (Oliveira, Almada, 1998; Oliveira, 2004). In addition, are expected, since the evolutionary mechanism favored juveniles C. paranaense are known for their aggressive differences in social behavior between these two large interactions and establish social hierarchy (see Brandão groups (Keenleyside, 1991; Barlow, 2000). In a recent study et al., 2015, 2018). Thirty-one individuals of similar size with juvenile Amazonian cichlid, Pterophyllum scalare (mean ± S.E. = 68.1 ± 0.08 mm), weight (mean ± S.E. = (Schultze, 1823), Gauy et al. (2018) found that chemical 14.14 ± 0.47 g) and age were euthanized to examine the information is important to keep social stability within the gonadal development using a microscope, confirming that group. For instance, the greater the renewal of aquarium individuals were indeed juveniles (classification according water (and the more diluted chemical information), the to Babiker, Ibrahim, 1979). A voucher specimen was greater the overt aggression in aggressive interactions, placed in UNESP’s fish collection, São José do Rio Preto, and longer time was needed to restore the baseline levels SP, Brazil, (DZSJRP-Pisces 13046). of aggression in the group. This finding suggests that the response to chemical cues seems to follow a pattern for Experimental design. The effect of water renewal on cichlid’s social communication. aggressive interactions was tested in groups of three C. In previous studies in our laboratory, however, we paranaense without sex identification assigned to one out of observed some differences in the aggressive behavior two treatments: 1) 0% [T0%] water renewal (control); and 2) patterns for Cichlasoma paranaense Kullander, 1983 50% [T50%] water renewal (amount of water renewal that and those expected for cichlids (personal observations). has the greatest effect on other cichlids; see Gonçalves-de- After setting