Light intensity affects aggressive behavior in fish because this variable influences physiological processes. Such effects could, however, vary according to the species and the ontogenetic stage of life because different life history can modulate behavior. Thus, we compared the effect of light intensity on the agonistic behavior of juvenile cichlids acará tinga Geophagus proximus, Nile tilapia Oreochromis niloticus, and the angelfish Pterophyllum scalare under low and high light intensity conditions. Fish were isolated in 36 l-aquaria for 96 h and paired (resident-intruder) until hierarchy settlement, while agonistic interactions were recorded. High light intensity increased latency to fighting in G. proximus and O. niloticus, but did not affect it in P. scalare. High light intensity also affected the occurrence of several other agonistic behaviors (chase, circling, lateral fight, frontal display, and mouth fight) but in different ways across the three species. We conclude that mechanisms underlying these data reflect differences in the natural history of the cichlid species.

Brycon amazonicus is a native Amazonian fish that is important for aquaculture in South America. Larval mortality is high in this species in intensive breeding systems due to aggressiveness among larvae. The present study investigated experimentally the effects of body size heterogeneity on the aggressive behavior and survival of B. amazonicus during the early stages of larval development. Two treatments (larvae groups with homogeneous and heterogeneous body size) were evaluated throughout early larval stages tested at six time points: 12, 24, 36, 48, 60 and 72 hours after hatching (HAH). Two experiments quantified, respectively, aggressive interactions and mortality rates among larvae at each time point. The frequency of aggressive interactions exhibited by the less aggressive larvae in each replicate was higher in the homogeneous size treatment. Aggressiveness was higher at 12 HAH, decreasing thereafter, and increasing again at 72 HAH. The mortality rate significantly increased with the larval stage, and was higher in the homogeneous than in the heterogeneous sized groups. Our results showed that aggressiveness in B. amazonicus larvae is affected by size variability and larval development stage. This knowledge about larval behavior is important to develop measures to improve larval health and survival in intensive production systems for this species.

We evaluated the effect of light intensity on survival rate and zootechnical performance in matrinxã larvae (Brycon amazonicus) that is an important species for fish farming in the Amazon region. For this, the larvae were submitted to three experimental stages: Stage I—10–72 hr after hatching (HAH), Stage II—72–168 HAH and Stage III—168–288 HAH. The animals were submitted to three treatments of different light intensities: low (±20 lx), intermediate (±200 lx) and high (±2,000 lx). The low light intensity increased the survival rate in 24, 48, 72, 120, 168 and 288 HAH. The size of the animals was homogeneous in 72 and 168 HAH in the low and intermediate treatments. The high light intensity increased the zootechnical parameters in 288 HAH. We suggest the use of low light intensity in the initial periods of observation (24 and 48 HAH) to reduce aggressiveness and increase the survival and homogeneity of the animals. On the other hand, it is possible to suggest an increase in the light intensity in the final period of observation (288 HAH), as the increase in intensity stimulated growth and affected the survival rate of the matrinxã larvae.

Environmental changes can cause physiological alterations in fish, which may affect some behavioral patterns. We evaluated the effects of water temperature on the aggressive behavior of male freshwater angelfish, Pterophyllum scalare. We subjected pairs to three water temperature conditions: low (23.8 ± 0.8°C), medium (27.9 ± 1.2°C), and high (31.7 ± 1.0°C), with eight repetitions each. We assessed latency to fighting, aggressive interaction frequency, and territorial defense. In low and high temperatures there was a reduction in aggressive behavior exhibitions in comparison to medium temperatures (P < 0.05). As a result, water temperature can influence aggressive motivation and territorial establishment, given that temperatures closer to species optima (27.9 ± 1.2°C) can favor social contests for an Amazonian ornamental cichlid species, P. scalare.