Ritmo diário da atividade locomotora em uma arraia amazônica, Potamotrygon wallacei (Chondrichthyes: Potamotrygonidae)

Abstract

Different organisms, including vertebrates, perform routine activities during their life cycles that may vary rhythmically on a daily or seasonal basis. Thus, the present study aimed to characterize the daily rhythm of locomotor activity and its effects on behavioral parameters in the cururu stingray, Potamotrygon wallacei, in an artificial environment. For this, 10 stingrays were individually distributed in experimental aquariums (100 L volume) and submitted to continuous recordings of their daily activity for three consecutive days. Based on these video analyses, an ethogram was created with the description of the behavioral units. Ten units were identified (n=10), nine related to activity (swimming and movement with and without displacement) and one to rest. With these units in hand, the frequency was quantified, analyzing the first 10 minutes of each hour, totaling 120 hours of observation. For a better visualization of the activity, all units focused on this behavioral manifestation were grouped, constituting two groups: total activity and rest. In addition, the duration (s), distance traveled (cm) and average speed (cm/s) were also evaluated using a software (Fish Track v0.4), which quantified them during a complete period of 24 hours of a day. The existence of a rhythmic pattern was assessed and confirmed by using the Cosinor method, which defined the acrophases (peak periods) for the analyzed variables. The results obtained for the three grouped days revealed an acrophase for activity at 12:36h and for rest at 23:29h. The duration, distance traveled, and average speed also showed acrophases that indicate greater locomotor activity in the photic period of the day. These results together indicate that P. wallacei presents a diurnal rhythmic pattern, contrasting with the initial hypothesis of this study, of a predominantly nocturnal locomotor activity. Future investigations in a natural environment would be desirable to corroborate the findings obtained in the present study in relation to the rhythmic pattern of locomotor activity for the cururu stingray.