Estratégia de predação e tamanho dos indivíduos medeiam o efeito de secas e cheias sobre a condição corpórea em peixes piscívoros

Abstract

In the Amazon basin, climate change is characterized by an alteration in the spatial and temporal variation of rainfall, increasing the frequency of drought and severe flood events in rivers. Changes in this regime have directly impacted the aquatic environments of and organisms that inhabit the amazonian floodplains. The biological cycles of these organisms have strongly evolved to the predictive hydrological seasonality, reproductive seasonality is synchronized with the seasonal conditions for fat storage and offspring survival, which in turn are associated with food availability. During the low-water season, piscivorous fish have the best opportunity to prey, increasing energy surplus to reproduce and grow. Thus, weak low-water seasons or strong floods can limit these processes as the large volume of water reduces foraging success. However, the effect of these events may vary between exclusively piscivorous species and carnivorous-piscivorous species. In this study, we evaluated the effect of the intensity of droughts and floods and the size of individuals on the body condition of two piscivorous species: Acestrorhynchus falcirostris, exclusive piscivore, and Pellona flavipinnis, piscivore-carnivore. Data were obtained from standardized monthly collections in Lake Catalão, near Manaus, between 1999 and 2019. The severity of the hydrological events was based on the calculation of the anomaly of the event, from annual values of minimum and maximum river quota. Black for the past 115 years. The individual body condition was estimated by the relative condition factor, Kn of LeCren. For both species, individuals were classified into size classes, defined from the total variation of standard length and size of sexual maturity. The effect of individual size, severity of hydrological events and its interaction on KN was tested using generalized linear models, separately for the dry and flood periods and for each of the species. We found that the Kn of P. flavipinnis varied as a function of low-water season severity, with the Kn being lower during severe droughts. This suggests that severe drought imposes less feeding activity even for a carnivorous-piscivorous species. During the flood period, Kn was affected by the interaction between flood severity and individual size. Larger individuals had higher Kn during strong floods and lower during mild floods, while smaller individuals were indifferent to flood severity. These combined results suggest some degree of dependence of P. flavippinis on the animal resource from the flooded forest. For A. falcirostris, smaller individuals showed lower Kn during mild low- water compared to severe droughts, suggesting that the greater volume of water limits the chances of predation for them. In flood, individuals of all size classes have lower Kn in strong floods compared to light floods. However, larger individuals have a much greater loss of body condition than smaller individuals. These results suggest that young-adults of A. falcirostris, which are in the first reproduction, are more impacted by mild low-water events, which seems to reduce prey capture and surplus energy , while senior-adults are more impacted by strong floods. Larger individuals seem to face insuficiente energy intake to recover the large energy expended to reproduce a few months before due to the very low rate of encounter with prey for energy replacement and the higher cost of foraging in conditions of high-water velocity. Our results indicate that, although by different processes and in different ways, both species are impacted by hydrological events that deviate from normal.