DOI: 10.5061/dryad.np5hqbztt
title: Seed predation by amazon fish

description: Our experiment revealed unexpected behavioral strategies involved in seed
 predation of Mabea fistulifera by fish (Brycon cephalus), including
 temporal storage of seeds in the stomach followed by regurgitation and
 reingestion of individual seeds. Larger fish were faster at removing the
 seed coat and exposing the endosperm, due to precise oral manipulation of
 seeds.
description: Our experiment was conducted at the Laboratorio de
 Ictiologia Tropical (LIT) of the Federal University of Mato Grosso,
 Brazil, for 12 days during July 2019. <i>Brycon cephalus</i>
 individuals (<i>N</i> = 8, 10.1-28.0 cm standard length;
 maximum length is 45 cm TL, www.FishBase.org) were retrieved from a nearby
 fish-farm. Individual fish were kept in 61-liter aquaria, equipped with a
 water recirculation system, and water quality was monitored daily
 (temperature: 28.5 ± 0.6 ºC, pH: 7.03 ± 0.04, and dissolved oxygen 5.78 ±
 0.42 mg/L). Aquaria
 were protected with a dark screen, containing a small opening for the
 observer, aiming not to cause an observer's effect on the fish's
 behavior (Sabino & Carvalho, 2008), and equipped with remotely
 operated Go Pro cameras positioned above and on the sides of the tanks.
 During the experiment, focal fish were fed daily at 0800 h with individual
 seeds (one by one) extracted from ripe fruits of <i>Mabea
 fistulifera </i>(seed width: 6.04 ± 0.77 mm, length: 8.48 ± 0.22 mm,
 weight: 0.5 ± 0.4 g) and later, at 1700 h with extruded commercial feed,
 aiming to complement the species' diet. <i>Mabea
 fistulifera</i> Mart. (Euphorbiaceae) is a pioneer tree, commonly
 found in riparian forests. The fruit is a dry, subglobous capsule (length:
 ≈ 15.5–19.0 mm), whose epimesocarp
 cracks in explosive dehiscence, expelling the seeds (Vieira, 1991). Seed
 ingestion occurred ad libitum (Altmann,
 1974), where we considered as
 satiated a fish that did not show interest on a seed after 15 min of it
 being offered. At that point, we removed non-consumed seeds.
 Observations during a pilot trial revealed that <i>B.
 cephalus</i> regurgitate seeds. Thus, we searched the tanks
 for regurgitated seeds at 15-min intervals, during 4 hrs. after the last
 feeding event. After 4 hrs., visual surveys were extended to 30-min
 intervals until the last regurgitated seed was observed (i.e., the fish
 regurgitated all the ingested seeds). We repeated the experiment four
 times per fish, with a 24 h period between
 trials. We
 assessed four metrics of seed predation including: the (1) number of seeds
 ingested (NSI); (2) time to regurgitation of the first seed (TRFS),
 defined as the period between the ingestion of the last seed, without the
 fish having any food in their mouth, until the beginning of the oral
 manipulation activity; (3) time to regurgitation of the last seed (TRLS),
 defined as the period between the ingestion of the last seed, without the
 fish having any food in the mouth, until the time when oral manipulation
 activity of the last regurgitated seed was observed; and (4) handling time
 (HT), defined as the average time to chew each regurgitated seed that was
 reingested. We analyzed whether fish size influences these metrics of seed
 predation via separated mixed effects regression models, where fish size
 was the predictor variable and fish identity was included as a random
 effect to account for the lack of independence between multiple trials (N
 = 4) per fish. Prior to analysis, we transformed NSI via square root to
 enhance homogeneity of the variance. Regression models were implemented in
 R (version 3.6.3), package lme4 (Bates et al., 2015); significance of the
 fixed factor was assessed with Wald’s test, package car (Fox &
 Weisberg, 2019); plots were created in package ggplot2 (Wickham,
 2016).