Effects of anomalous climatic events on the structure of fish larvae assemblages in the eastern Amazon

The reproduction of neotropical fish is linked to environmental stimuli that act as triggers in this process. Thus, it is possible to affirm that specific environmental changes can delimit most fish’s period and reproductive success. El Niño Southern Oscillation phenomena (ENSO) influence rainfall and, consequently, hydrological dynamics, affecting several fish population aspects, especially reproductive aspects. However, in the Amazon, empirical evidence of the effect of anomalous climatic events on fish reproduction is incipient. In this sense, we investigated the taxonomic and functional structure of parental fish larvae stocks and how species modulate their reproductive activities before (2013 and 2014) and during La Niña (2018) and El Niño (2019) events. The data evidence that the larval assemblages suffered alterations in the taxonomic and functional composition between the three analyzed periods and a pattern of temporal distribution with a high influence of environmental variables. Flow, pH, and electrical conductivity were the most important variables to modulate fish reproductive intensity between periods. The species seem to respond to combinations of these variables that reflect environmental conditions conducive to biological recruitment according to their ecological characteristics, allowing the perpetuation or decline of their abundance in each period. All species of commercial interest associated with the neutral period showed a sharp decline in the subsequent moments. These results suggest that the incidence of anomalous climatic events added to regional fisheries exploitation can negatively affect the phenology and demographic patterns of larvae assemblages on a short temporal scale. During the neutral period, the community was dominated by larvae of periodic large, herbivores, piscivores, epibenthic maneuverable, and nektonic burst swimmers. The decrease in the abundance of certain functional groups at the neutral and La Niña period favored an accelerated ecological succession during the El Niño period, due to the increase of species from basal trophic levels (planktivores), generalists (omnivores), highly resilient (intermediate strategists), sedentary, short-distance migrants and little commercially exploited. Thus, the results contribute to the understanding of the interactions between anomalous climatic events and the reproduction of fish with different ecological characteristics in the Amazon River

DESCRIÇÃO MORFOLÓGICA DO DESENVOLVIMENTO INICIAL DE Brycon amazonicus (CHARACIFORMES, BRYCONIDAE) DO BAIXO AMAZONAS, PARÁ

The present study characterized the initial development of matrinxã Brycon amazonicus (Agassiz, 1829), as well as the changes in allometric growth patterns during the initial ontogeny of the species. A total of 260 laravae from induced reproduction were analyzed for morphometric and meristic variables, as well as the coeffient of allometric growth in relation to head and body length. The initial larvae (3.9 to 5.9 mm) of B. amazonicus are transparent and have a relatively large and elongated yolk sac. In the pre-flexion stage (5,9 to 7,6 mm) the larvae presented dendritic pigmentation in the upper region of the head and pointed along the upper region of the swimming bladder. At the flexion (8,3 to 13,5 mm) and post-flexion (15 to 26 mm), pigmentation intensifies with pigments (dendrict and punctiform) distributing mainly in the upper region of the head, lateral dorsum of the body and along the lateral line.Keywords: Initial development; morphology; negative allometry; fish; matrinxã.O presente estudo caracterizou o desenvolvimento inicial do matrinxã, Brycon amazonicus (Agassiz, 1829), bem como as mudanças nos padrões de crescimento alométrico durante a ontogenia inicial da espécie. Um total de 260 larvas provenientes de reprodução induzida foram analisados quanto as variáveis morfométricas e merísticas, além do coeficiente de crescimento alométrico em relação ao comprimento da cabeça e do corpo. As larvas iniciais (3,9 a 5,9 mm) de B. amazonicus apresentam-se transparentes e com saco vitelínico relativamente grande e alongado. No estágio de pré-flexão (5,9 a 7,6 mm) as larvas apresentaram pigmentação dendrítica na região superior da cabeça e puntiformes ao longo da região superior da bexiga natatória. Nos estágios de flexão (8,3 a 13,5 mm) e pós-flexão (15 a 26 mm), a pigmentação se intensifica com pigmentos (dendríticos e puntiformes) distribuindo-se principalmente na região superior da cabeça, dorso lateral do corpo e ao longo da linha lateral.Palavras-chave: Alometria negativa; desenvolvimento inicial; morfologia; peixe; matrinxã

Early life history of two Neotropical Triportheidae fish (Characiformes)

Abstract The early ontogeny of Triportheus albus and T. angulatus, two fish species of Triportheidae, is described using morphological, meristic, and morphometric characters. These species are exploited by subsistence fisheries and have potential as an alternative source of fish, given the decline in the natural stocks of other commercially important fish species in the Amazon. The specimens were collected in the open water limnetic zone, under of the macrophyte stands, and in subsurface areas near sandbars in the Amazon basin. Intra and interspecific morphometric analyzes were performed to evaluate growth models between species. The combination of color pattern, body morphology, morphometric proportions and myomeres number distinguishes the species from each other and from other congeners. Some morphometric relationships related to head as snout length and eye diameter as well as length from the snout to the origins of anal and length from the snout to the origins of pelvic, related with standard length were different between the two species of Triportheus, reflecting different growth models between them. An identification key for larvae and juveniles of some species of Triportheus from the Eastern Amazon is presented

Table1_Effects of anomalous climatic events on the structure of fish larvae assemblages in the eastern Amazon.DOCX

The reproduction of neotropical fish is linked to environmental stimuli that act as triggers in this process. Thus, it is possible to affirm that specific environmental changes can delimit most fish’s period and reproductive success. El Niño Southern Oscillation phenomena (ENSO) influence rainfall and, consequently, hydrological dynamics, affecting several fish population aspects, especially reproductive aspects. However, in the Amazon, empirical evidence of the effect of anomalous climatic events on fish reproduction is incipient. In this sense, we investigated the taxonomic and functional structure of parental fish larvae stocks and how species modulate their reproductive activities before (2013 and 2014) and during La Niña (2018) and El Niño (2019) events. The data evidence that the larval assemblages suffered alterations in the taxonomic and functional composition between the three analyzed periods and a pattern of temporal distribution with a high influence of environmental variables. Flow, pH, and electrical conductivity were the most important variables to modulate fish reproductive intensity between periods. The species seem to respond to combinations of these variables that reflect environmental conditions conducive to biological recruitment according to their ecological characteristics, allowing the perpetuation or decline of their abundance in each period. All species of commercial interest associated with the neutral period showed a sharp decline in the subsequent moments. These results suggest that the incidence of anomalous climatic events added to regional fisheries exploitation can negatively affect the phenology and demographic patterns of larvae assemblages on a short temporal scale. During the neutral period, the community was dominated by larvae of periodic large, herbivores, piscivores, epibenthic maneuverable, and nektonic burst swimmers. The decrease in the abundance of certain functional groups at the neutral and La Niña period favored an accelerated ecological succession during the El Niño period, due to the increase of species from basal trophic levels (planktivores), generalists (omnivores), highly resilient (intermediate strategists), sedentary, short-distance migrants and little commercially exploited. Thus, the results contribute to the understanding of the interactions between anomalous climatic events and the reproduction of fish with different ecological characteristics in the Amazon River.</p