Among the environmental variables, temperature was the most important and the Mantel test detected a significant correlation between temperature and the densities, only for P. lineatus (r = 0.09, p = 0.03). The species in our data chose for spawning tributaries that are not dammed, of which most are outside conservation areas. Therefore, recruitment, maintenance and possible actions aiming to recover the stocks of these species are dependent on the conservation of tributaries and floodplain lakes in the region, in addition to monitoring to prevent fishing during the reproductive period.

Summary This study provides information on the reproductive biology of the dorado Salminus brasiliensis from the Cuiabá River basin, through determinating life history trajectories (length at first maturity, fecundity and spawning type) and the reproductive period, thus establishing the relationships between biotic factors and rainfall and river levels that might act as potential triggers for maturation and spawning. Salminus brasiliensis is a migratory species of great commercial and ecological importance. Individuals were collected monthly from August 2013 to July 2014 in the Cuiabá River. Analyses were performed based on biometric data and the gonads. Females attained greater lengths than males in the Cuiabá River basin, and with a significant difference in the sex ratio in favor of females. Peak reproductive activity occurred in November and December and was related to rainfall. Reproduction was seasonal, with spawning and reproductive potential correlating positively with the length and mass of the gonads of mature females. Average length at first maturity for females was estimated at 55 cm. A regular (annual) monitoring programme of essential biological variables to support a trend analysis over years (not just a snapshot study, as this one) is strongly recommended in order to give advice for the proper fishing policies in the region, as without regular basic data on the population dynamics, management is not possible.

The aim of this study was to compare the reproductive processes of two large catfishes, Pseudoplatystoma corruscans and Pseudoplatystoma reticulatum, from the Cuiabá River Basin. The reproductive process were assessed to: (i) characterizing the population structure and sex ratio; (ii) determining the reproductive period; (iii) estimating and quantify the nutritional status and energy reserves and their relationships with reproductive stages; and (iv) estimating the body length at first gonad maturation (TL 50 ). Individuals were sampled monthly from July 2006 to February 2008 using gill nets, seine nets, hooks, casting nets and trotlines. In addition, 294 individuals were obtained from the artisanal fishery in the city of Cuiabá, Mato Grosso state, Brazil.Total lengths were greater for females for both species, with no significant difference in the sex ratio; growth was considered isometric, except for P. corruscans males. Peak reproductive activity was in December and January. Differences in the hepatosomatic index (HSI) in P. corruscans depended on the gender. In P. reticulatum the HSI did not differ between sexes or among developmental stages. For P. corruscans, the estimated mean total length at first maturity (TL 50 ) was 62.92 cm, and for P. reticulatum 57.84 cm.Action to ensure the protection of the fish stocks should consider their reproduction processes, which are important for the equilibrium of these populations in the Cuiabá River, as well as for fisheries management.