This work investigates life strategy elements of the neotropical cichlid Aequidens tetramerus in the lakes of Central Amazon várzea, predominated by white waters. During the 2011 hydrological cycle, fish were captured monthly from banks of aquatic macrophytes present in the lakes studied. The animals found had total maximum lengths of 18.5 cm and 20 cm for females and males, respectively. The average length recorded for their first sexual maturation was 6.49 cm and 8.35 cm for females and males, respectively. Species reproduction occurred throughout the hydrological cycle, but the peak of the reproductive activity was observed during the period of rising water. The average fertility was 1,477 oocytes. The diametric distribution of these oocytes showed synchronous development in more than two groups, suggesting partial spawning. It seems that A. tetramerus reaches sexual maturation early in its life time. Based on the reproductive attributes unveiled in this study and on the fact that the species performs parental care, it is suggested that this is a predominantly K-strategist species. RESUMOEste trabalho investiga aspectos da estratégia de vida do ciclídeo neotropical Aequidens tetramerus em lagos de várzea na Amazônia Central, ambientes dominados por águas brancas. Os peixes foram capturados mensalmente durante todo o ciclo hidrológico de 2011 em bancos de macrófitas aquáticas presentes nos lagos estudados. Foram encontrados animais com comprimentos totais máximos de 18,5 cm e 20 cm para fêmeas e machos, respectivamente. O comprimento médio encontrado para a primeira maturação sexual foi de 6,49 cm e 8,35 cm para fêmeas e machos, respectivamente. A reprodução da espécie ocorreu durante todo o ciclo hidrológico, mas foi observado um pico de atividade reprodutiva no período da enchente. A fecundidade média foi de 1.477 oócitos. A distribuição diamétrica destes oócitos evidenciou um desenvolvimento sincrônico em mais de dois grupos, sugerindo uma desova parcelada. Aparentemente A. tetramerus atinge precocemente a sua maturação sexual. As maiorias dos atributos reprodutivos levantados neste estudo, e o fato da espécie apresentar cuidado parental, indicam que ela seja predominantemente uma espécie K-estrategista.

We describe the most important reproductive aspects of the flag cichlid Mesonauta insignis in the floodplain (várzea) lakes of the Central Brazilian Amazon. Between September 2005 and August 2006, fish were collected monthly from mattresses of aquatic macrophytes. Biometric measurements as well as macroscopic and microscopic analyses of the gonads were performed. Standard body lengths ranged from 2.4 to 9.3 cm, and weight−length relationships were indicative of isometric growth patterns. Reproduction events were detected in all months, but the gonadosomatic index indicated a reproductive season from October to February (during low and rising water periods), reaching a reproductive peak in February. Average fecundity was 1184 ± 40.82 (mean ± SD) mature oocytes. M. insignis exhibits an asynchronous oocytal development, characteristic of multiple spawnings. Morphological and histological analyses indicated 5 gonadal maturation stages for females. Average standard length at first sexual maturation was 5.18 cm for females and 5.5 cm for males. M. insignis shows late sexual maturation. Taken together, these aspects suggest that a life history strategy of 'equilibrium' predominates in the species; consequently, M. insignis can be considered vulnerable to high extraction rates, and can only be exploited sustainably if adequate precautionary management procedures are adopted. Some management measures are suggested for the exploitation of this species in the Central Amazon.