Reis‑Filho and Leduc Helgol Mar Res (2018) 72:7 https://doi.org/10.1186/s10152-018-0511-9 Helgoland Marine Research SHORT COMMUNICATION Open Access Mysterious and elaborated: the reproductive behavior of the rhomboid mojarra, Diapterus rhombeus (Cuvier, 1829), in Brazilian mangrove habitats José Amorim Reis‑Filho1,2* and Antoine O. H. C. Leduc1 Abstract Many fsh species have behavioral traits related to reproduction that aim to improve egg conditions and survival of early life stages. Here, we provide the frst detailed description of reproductive strategies performed by the rhom‑ boid mojarra, Diapterus rhombeus. We based this description on several mating events, which occurred in man‑ groves located in Todos os Santos Bay, Brazil. These spawning events occurred at the mangrove fringe in the month of August in 2013 and 2014, which suggests that these spawning events occur predictably in space and time. Two principal behavioral tactics were observed and involved breeding aggregation and a unique nest-clearing behavior. Following these behaviors, many fsh exhibited an extreme lethargic state during which they took refuge amidst mangrove roots. Overall, these observations revealed an unexpected and uncommon set of behaviors in an otherwise well-studied species. The present study not only highlights basic gaps in our understanding of estuarine species but also suggests that future investigations are poised to yield exciting and insightful fndings. Keywords: Diapterus rhombeus, Reproduction, Behavioral expression, Mangrove habitat, Conservation Background or, alternatively, to uniparental or biparental care [6, 7]. Improving our knowledge of the behavioral and life his- Tus, it is imperative to understand that each of these tory traits of marine fshes has often resulted in a better behavioral traits is able to afect population trajectories understanding of the factors regulating their productivity in distinct ways. For example, improving reproductive and thereby has provided managers and conservationists success (including ofspring survival) requires individu- with much-needed information for guiding sustainable als to adjust their phenotype to either face environmental exploitation [1–3]. While documenting the spatiotem- changes and/or to meet specifc requirements associated poral characteristics associated with the reproductive with their life cycle (e.g., breeding period). In turn, the behavior of many organisms is common, the results gen- relative success of each of these behavioral patterns may erated must be thoroughly understood in terms of the have substantial consequences for population growth and population structure and habitat requirement of the spe- permanence in the wild [8]. cies if helpful guidance for management is sought [4]. Maximizing lifetime reproductive success often For example, teleost fshes are characterized by a wide requires that individuals undergo a range of behavio- range of reproductive behaviors, ranging from large ral modalities (e.g., courtship, mating, and territorial spawning aggregations [5] to an absence of parental care defense), each of which may be regulated by the prevail- ing environmental context [9–11]. For example, in many marine fsh species, suitable spawning grounds constitute *Correspondence: [email protected] 1 Instituto de Biologia, Universidade Federal da Bahia, Campi Ondina, a resource of prime importance to successfully repro- Salvador, BA, Brazil duce [12–14]. Tus, accurate records and identifca- Full list of author information is available at the end of the article tions of these spawning habitats are crucial to promote © The Author(s) 2018. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creat​iveco​mmons​.org/licen​ses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Reis‑Filho and Leduc Helgol Mar Res (2018) 72:7 Page 2 of 6 useful conservation practices and sustainable fsheries, conducted between 0700 am and 1100 am, which corre- and given the complexity of many spawning systems (i.e., sponded to the occurrence of the reproductive strategies. often involving a range of behaviors as detailed above), Te records were conducted while snorkeling in the man- a thorough understanding of how these sites are used grove sites located on two islands within Todos os Santos for spawning also becomes essential [5]. However, for Bay (TSB) (i.e., Itaparica Island and Frade Island; approx. most estuarine systems, given their high sediment load- 12°50′S, 38°50′W), which is itself located of the Brazil- ing, these habitats are visually impenetrable, which often ian central coast. Te total embayment of TSB is nearly prevents detailed observations from being conducted 1100 m2. [but see 15]. Tus, this common estuarine characteristic In each of the 2 years of study, we observed shoals implies that only indirect evaluation of habitat require- containing 350 to 700 D. rhombeus individuals esti- ments can be made for most species. mated to range in size from 6 to 18 cm TL. Of these, 35 Te rhomboid mojarra (Diapterus rhombeus) is a com- and 50 individuals (2013 and 2014, respectively) were mon and widely distributed marine and estuarine fsh caught using a manual trap, allowing us to determine whose presence in the Western Atlantic spans from Flor- the gonadal stage of each of the captured individuals. ida to Brazil [16]. Tis species is one of the most abun- For this purpose, we used a stereomicroscope or, when dant demersal fshes of embayments located in Central possible, a macroscopic approach. For instance, females and South America. Adults can reach up to 210 mm in ripe for spawning present intense yellow color at the total length (TL) [17] and are usually found aggregat- gonads and a high concentration of surface blood ves- ing in small groups (e.g., 20 individuals). Te diet of D. sels and oocytes, while over 70% of the celomatic cavity rhombeus is mainly composed of benthic and pelagic is occupied by gonads in their mature stage [22]. Of the invertebrates, including Polychaeta and Crustacea [18, fsh caught in 2013 and 2014, 89.7 and 90.4% presented 19]. Along the Brazilian coasts, this species typically mature gonads, respectively. occurs in mangroves (dominated by either mature forests For our behavioral observations, we used the ‘focal ani- or fringe fragments), in estuaries and in relatively shal- mal’ approach, which involved documenting any observ- low bays (depth of 0.2–30 m; [15]). Despite the low depth able behaviors [23, 24]. Specifcally, an observer (JAR-F) at which D. rhombeus is typically found, this species is positioned himself at approximately 1.5–2.0 m from the adapted to low-visibility conditions resulting from high focal individual to conduct observations. Te records levels of suspended sediments, i.e., those which often were made on plastic sheets and by using a portable ™ characterize estuarine environments. As such, the condi- video camera (GoPro Hero 3+ with the resolution set tions under which this species occurs have often impeded to 12 megapixels). researchers and managers from studying its ecology and behavior. While various studies have described the repro- Results ductive cycle of the rhomboid mojarra [17, 18, 20, 21], we In seven and eight of the 10 mangrove sites (in 2013 and have scant information on the breeding behavior of this 2014, respectively), we observed D. rhombeus perform- species in the wild. To some extent, this defciency may ing intense mating behavior. Te behavioral repertoire be palliated by behavioral studies conducted in captivity; of the rhomboid mojarra includes individual and group however, biases associated with this behavioral trait are movements, which is reminiscent of a breeding aggrega- bound to occur as a result of the venue (non-natural con- tion. Tis behavior was then followed by a nest-clearing ditions) under which observations were conducted. behavior. We observed these behaviors for approximately To understand the processes governing the breeding 3 h, during which fsh exhibited an uncommon and pecu- behavior of this abundant tropical fsh, we conducted liar swimming behavior (see Additional fle 1: Supple- directed observation in the wild. While the high-turbidity mentary video at https ://vimeo .com/26298 7523). Tis contexts under which this species occurs often impede behavior may be characterized as a series of seemingly conducting direct observations, the behavior described erratic and abrupt movements, which includes frequent here results from observations taken in clear-water (i.e., shifts in direction and high-speed bursts of swimming low-turbidity) mangroves. among the mangrove prop roots and propagules. Sur- prisingly, after this behavioral display, many individuals Materials and methods exhibited yet another uncommon behavior, in which each In 2013 and 2014, we carried out monthly dives in 10 individual voluntarily “trapped” itself among mangrove mangroves characterized by the presence of Avicen- prop roots while continuing to breathe (Fig. 1). Individu- nia schaueriana and Rhizophora mangle forests. Each als remained in this state and confned among root struc- of these free dives lasted approximately 6 h and was tures for a period ranging from 2 to 15 min (average of restricted to a given sampling area. Observations were 7.4 min) (Fig. 2a). Approximately