Jesús Nuñez

Life-history characteristics of the large Amazonian migratory catfish Brachyplatystoma rousseauxii in the Iquitos region, Peru.

The main life-history traits of the dorado Brachyplatystoma rousseauxii, a large Amazonian catfish undertaking the largest migration known for a freshwater fish species (from the nursery area in the estuary of the Amazon to the breeding zones in the head waters of the western Amazon basin close to the Andes), were determined from a 5 year sampling of >15,000 specimens in the Peruvian Amazon. The breeding season occurred during the falling and low-water periods, which is hypothesized to be an adaptation to maximize the chances of young stages to reach the estuary. The size at first sexual maturity was slightly larger for females than males, c. 91 and 83 cm standard length (L(S)), respectively. Both males and females reproduce for the first time at >3 years old. The fecundity per spawning event ranged from 481,734 to 1,045,284 oocytes for females weighing 25 and 34 kg, respectively. Seasonal variations of body condition were similar among sexes, but differed between immature specimens that had a higher condition during the low-water period and lower condition during rising waters, and mature individuals that showed the opposite pattern. The growth characteristics were estimated by L(S) frequency analysis. For females, the best fitting models gave a mean birth date in August, during the height of the breeding cycle, with the following von Bertalanffy growth function parameters: L(Sinfinity) = 153.3, K = 0.29 and t(0) =- 0.37 years. For males, the best fitting model gave a mean birth date in July, also during the height of the breeding period, with L(Sinfinity) = 142, K = 0.30 and t(0) =- 0.36 years. At a given age, females were systematically larger than males and the size difference increased with age. The largest females sampled (148 cm L(S)) was 11 years old and the largest male (134 cm L(S)) was 9 years old. The mortality estimates were higher for males total (Z) = 1.34, natural (M) = 0.52 and fishing (F) = 0.82 than for females (Z = 0.98, M = 0.50, F = 0.48). The life-history patterns of B. rousseauxii are discussed in light of the available knowledge about this species and the understanding of its complex life cycle.

Gender determination in the Paiche or Pirarucu (Arapaima gigas) using plasma vitellogenin, 17β-estradiol, and 11-ketotestosterone levels

Arapaima gigas is an air-breathing giant fish of Amazonian rivers. Given its great economic and cultural importance, the aquaculture development of this species represents an evident solution to face the decline of wild populations. In captivity, reproduction occurs generally in large earthen ponds where stocks of a few tens of brooders are maintained together at the beginning of the rainy season (December–March in the Peruvian Amazon). Fry production relies on the spontaneous formation of male and female pairs, which build a nest, delimit a territory and guard the offspring for at least 20xa0days from other congeners and predators. However, as sex determination of A.xa0gigas is not possible by morphological criteria, it is very difficult to optimize reproduction conditions and fry production in each pond, which seriously hampers the culture of this species. This situation prompted us to develop sexing methodologies based on (1) the detection of female specific plasma Vitellogenin (Vtg) using an enzyme immuno assay (EIA), and (2) the determination of plasma 17β-estradiol and 11-ketotestosterone levels for immature specimens. The Vtg purification was performed by electro-elution after polyacrilamide gel electrophoresis (PAGE) from plasma of 17β-estradiol treated A.xa0gigas juveniles. Two different Vtg molecules were isolated, (Vtg1 and Vtg2) with 184 and 112xa0kDa apparent molecular masses, respectively, and two antibodies were raised in rabbits for each Vtg molecule. Adult fish were 100% accurately sexed by Vtg EIA, while 100% of immature fish and 95% of adults were accurately sexed by 17β-Estradiol and 11-Ketestosterone ratios. We also observed different color pattern development in male and female adult fish (6-year-olds) around the reproductive period.

Age and growth of the Amazonian migratory catfish Brachyplatystoma rousseauxii in the Madeira River basin before the construction of dams

The goliath catfish Brachyplatystoma rousseauxii has crucial economical and ecological functions in the Amazon basin. Although its life history characteristics have been studied in the Amazon, there is little information in the Madeira River basin, which holds genetically distinct populations and where dams were recently built. Using fish collected in Bolivia, Brazil and Peru, this study provides a validation of growth rings deposition and details the growth patterns of B. rousseauxii in the Madeira before the dams’ construction. Age structure and growth parameters were determined from 497 otolith readings. The species exhibits two growth rings per year and sampled fish were between 0 and 16 years old. In the Brazilian portion of the basin, mainly young individuals below 5 years old were found, whereas older fish (> 5 years) were caught only in the Bolivian and Peruvian stretches, indicating that after migrating upstream to reproduce, adults remain in the headwaters of the Madeira River. Comparing with previous publications, B. rousseauxii had a slower growth and 20 cm lower maximum standard length in the Madeira River than in the Amazon River. This study provides a baseline for future evaluation of changes in population dynamics of the species following dams closure.