DOI: 10.5061/dryad.gtht76hws
title: Schooling behavior by two stream fish in Brazilian semiarid

description: Shoaling can provide a number of advantages for individual fish, enhancing
 foraging efficiency and reducing predation risk. We investigated the role
 of multiple characid species shoaling (Compsura heterura and Serrapinnus
 piaba) in order to recognize social behavior, foraging strategy, and diet
 composition in one semiarid stream, Northeast of Brazil. The study was
 done by field observations (ad libitum). The most frequent social
 behavioral (Arranged Mixed-species school - 38.46%) was represented by
 mixed-species schools structured with large-sized individuals of C.
 heterura using the school periphery and small individuals of both species
 using the center of the school. Shoals with lower individuals inhabiting
 shallow locals and pools presented higher frequency of this behavior.
 Although foraging behavior did not vary significantly between the two
 species, each characin species explored distinct food resources,
 indicating that diet segregation can act as a strategy to both species
 foraging in the same shoal. These results suggest that C. heterura and S.
 piaba have mechanisms to facilitate their coexistence in structured
 mixed-species schools, minimizing the costs of living in groups.
description: Behavior survey was performed along dry season in November 2011
 at daylight, following the <em>ad libitum</em>
 (<em>sensu</em> Lehner 1996) and focal animal sampling methods
 (Altmann 1974) through snorkeling sessions. The type of behavior presented
 by each group of fish was recorded, following Sabino (1999). Due to the
 morphological similarities of the two characids species, the diver (LRM)
 conducted 10 hours of preliminary observation in order to guarantee the
 correct identification of individuals. After that, the two species were
 identified underwater based on minor morphological differences (e.g. body
 height) and swimming performance (Figure 1). Additionally, individuals
 from both species were collected and identified by specialists. Voucher
 specimens were deposited in the ichthyological collection of the Fish
 Systematics and Morphology Laboratory at the Federal University of Paraíba
 (UFPB 7075, UFPB 7077). Diving sessions were conducted
 throughout the study area and the behavior was recorded every time a
 subject appeared in the visual field of the diver. All data were collected
 by the same diver (LRM) to avoid observer error. At the beginning of each
 diving session, the diver stood still for 10 min downstream of the site,
 so that the fish became used to the observer. Only fishes that appeared to
 be undisturbed by the observer’s presence were recorded. During the
 observation, the diver stayed in a fixed position and distant at least one
 (1) meter from the fishes. Each type of behavior was recorded using
 frequency method (presence/absence) and tabulated in one waterproof board
 during each diving session. A total of 31 h of active underwater
 observation was registered with several sessions of 30 min each, totaling
 62 observations with 30 min of interval between sessions.
 The sampling site was divided into seven sectors of 15 m each
 (Figure 1) based on habitats where shoals were located, totaling seven
 different observed shoals. The site presented clear and warm water with
 temperature around 30 ºC facilitating underwater sampling methods. Habitat
 descriptors (stream depth and water flow) were measured on each sector.
 Stream depth was measured using a measuring tape (in cm) considering the
 distance from water surface to stream bottom and water flow was measured
 with a fluxometer probe (in m/s). Behavior was grouped in two different
 categories: social and feeding (Table 1). Social behavior was classified
 into five categories: (i) disarranged mixed-species shoal - DS; (ii)
 arranged mixed-species school - AS; (iii) presence of predators - PP; (iv)
 predator attack - PA; and (v) reorganization - RE. Feeding behavior was
 classified into four categories: (i) foraging on the bottom - FB; (ii)
 foraging in the middle of the water column - FMI; (iii) foraging on the
 surface - FS; and (iv) foraging in the macrophytes - FMA. These behavior
 categories were defined after 10 h of previous underwater sessions based
 on different behaviors displayed by the entire shoal. Number of
 individuals on each shoal was also registered to determine shoal
 size. After behavior observations, 57 individuals of
 <em>S. piaba</em> and 54 individuals of <em>C.
 heterura</em> were sampled for diet analysis using seine nets (3.5 ×
 2.5 m, mesh size 5 mm) along the seven observed habitat sectors (Figure
 1). In each sector, the nets were passed twice during daylight. Each
 captured fish was euthanized using a 30 mL of a 10% clove oil solution in
 970 mL of water and then fixed in 10% formalin. Individuals were measured
 (Standard Length, cm) and stomach content analysis was performed following
 numerical and volumetric methods since both techniques are useful to
 represent the contribution of each food item on diet (Hyslop, 1980). Based
 on these techniques, we accessed the relative importance of each food item
 through the alimentary index (AI<em>i</em>) proposed by
 Kawakami & Vazzoler (1980) and adapted by Hahn et al. (1997),
 following the equation AI<em>i</em>=
 (F<em>i</em>*V<em>i</em>)/Σ
 F<em>i</em>*V<em>i</em>)*100,
 where <em>i</em> = 1, 2, ... n, food items;
 F<em>i</em> = frequency of occurrence of a given food item;
 V<em>i</em> = volume of a given food item.
description: # **Schooling behavior by two stream fish in Brazilian semiarid**
 [https://doi.org/10.5061/dryad.gtht76hws](https://doi.org/10.5061/dryad.gtht76hws) ## Description of the data and file structure ### Files and variables #### File: meus\_dados\_2024-11-05.xlsx **Description:** Schooling behavior in stream fish mixed-species shoal ##### Variables * Social behavior * Feeding behavior * Diet Behavior was grouped in two different categories: social and feeding. Social behavior was classified into five categories: (i) disarranged mixed-species shoal - aggregation of individuals of both species without arrangement; (ii) arranged mixed-species school - aggregation of individuals of both species with coordinated movements; (iii) presence of predators - aggregation of individuals with coordinated movements moving away from the predators; (iv) predator attack - aggregation of individuals moving rapidly after predator attacks; and (v) reorganization - reorganization of shoal following an attack. Feeding behavior was classified into four categories: (i) foraging on the bottom - individual investigates the bottom substrate for the presence of food items, which it ingests; (ii) foraging in the middle of the water column - individual investigates the middle of the water column for the presence of drifting food items, which it ingests; (iii) foraging on the surface - individual swims to the surface to ingest floating material; and (iv) foraging in the macrophytes - individual investigates macrophyte bed for the presence of food items. Stomach content analysis was performed following numerical and volumetric methods since both techniques are useful to represent the contribution of each food item on diet (Hyslop, 1980). Based on these techniques, we accessed the relative importance of each food item through the alimentary index (AI*i*) proposed by Kawakami & Vazzoler (1980) and adapted by Hahn et al. (1997), following the equation ![](file:////Users/luisamanna/Library/Group%20Containers/UBF8T346G9.Office/TemporaryItems/msohtmlclip/clip_image002.jpg)AI*i*= (F*i**V*i*)/Σ F*i**V*i*)*100 where i* = 1, 2, ... n, food items; Fi* = frequency of occurrence of a given food item; V*i* = volume of a given food item. ## Code/software All statistical analyses were performed in the R statistical and programming environment (R 3.3.1., R Development Core Team 2016) using “vegan” (Dixon 2003), “ade4” (Dray & Dufour 2007), “lme4” (Bates et al. 2015) and “car” (Fox & Weisberg 2019) packages.