Contrasted hydrological systems of the Peruvian Amazon induce differences in growth patterns of the silver arowana, Osteoglossum bicirrhosum

Abstract

-In Amazonian fisheries, the silver arowana, Osteoglossum bicirrhosum (Cuvier 1829) is heavily exploited for human consumption as an adult, and for the aquarium trade as a small juvenile (yolk sac juvenile mainly). The periodicity of annuli formation on otoliths and growth variability of the silver arowana were studied in different river river-basins of the Peruvian Amazon between 2006 and 2009. Transverse stained sections of 606 individual otoliths were analysed from four different river-basins, the Amazonas, Ucayali, Napo and Putumayo, of which 554 could be interpreted. These belonged to 274 females ranging from 15 to 91 cm (standard length) and 280 males ranging from 30 to 91 cm. In addition, yolk sac juveniles of known age were collected to improve growth modelling. Monthly proportions of stained otolith edges validated the formation of a single annulus per year in two different river-basins with lagged hydrological cycles: the Amazonas-Ucayali and the Putumayo. Stained growth mark counts resulted in a longevity estimate of at least 16 years for the silver arowana in the Peruvian Amazon. This fish grew quickly during the first two years, and asymptotic growth was reached after four to five years, except in the Putumayo where it was reached slightly earlier. Results showed no significant growth dimorphism between sexes within basins, but indicated significant growth differences among river basins. Silver arowanas measured, on average, between 38 and 40 cm at the end of their first year. Length-at-age differences among river basins increased with age to reach over 14 cm (and >3 kg) after 7 years between the faster and slower growing populations (Amazonas and Putumayo, respectively). The growth differences observed emphasize the need for further investigation on the population structure of this species as, although these differences might merely be phenotypic responses to contrasted environmental conditions, they could alternatively reflect the existence of several populations with distinct genetic and life history characteristics. The consequences of such differences would be very important for the management and conservation of this fragile and extensively exploited species.

Variations in reproductive strategy of the silver Arowana, Osteoglossum bicirrhosum Cuvier, 1829 from four sub-basins of the Peruvian Amazon

“…Important length and even more important body mass differences were observed between the four sub‐basins, as already noted while studying age and growth patterns of these same populations (Duponchelle et al., ). After reaching sexual maturity, fishes in the Amazonas become progressively heavier than those from the Ucayali, Napo and Putumayo, in order of increasing difference.…”

“…Age at first sexual maturity ( A m ) was calculated from the von Bertalanffy growth function (VBGF) as follows: where L m is the size at first sexual maturity previously calculated and t , L ∞ , K and t 0 the parameters of the VBGF obtained from Duponchelle et al. () on the same samples.…”

“…Choosing breeders from a population with higher relative fecundity (egg production per unit body mass), for example, might increase chances of success. A recent study in the Peruvian Amazon demonstrated important variations in the growth patterns of the silver Arowana in four sub‐basins, suggesting the existence of distinct populations that might require independent management (Duponchelle et al., ). The aim of the present study is to assess whether reproductive characteristics also vary, and to which extent, between and among these four sub‐basins of the Peruvian Amazon.…”

PRIMER ESTUDIO DE LA VARIABILIDAD GENÉTICA DE LA ARAHUANA Osteoglossum bicirrhosum (Cuvier, 1829) EN LA REGIÓN LORETO (AMAZONÍA PERUANA)

“…Nuestras observaciones de una estructura genética relacionada a la geografía son reforzadas por los obtenidos por Duponchelle et al (2012), en el análisis de crecimiento de O. bicirrhosum en cuatro cuencas (Amazonas, Ucayali, Napo y Putumayo, esta última es la misma población de Huapapa que la de nuestro estudio), a través del estudio de otolitos, encontraron que hay una importante variabilidad en el crecimiento de la especie en las cuencas estudiadas. Según los autores esto puede ser resultado de la plasticidad fenotípica de la especie, debido a la heterogeneidad del medio ambiente o a la existencia de varias poblaciones distintas en Perú, que necesitan ser manejados independientemente.…”

“…La demanda de alevinos de O. bicirrhosum se incrementó debido a que esta siendo comercializado como sustituto de Scleropages formosus (especie filogenéticamente hermana de la arahuana), en los mercados de peces ornamentales asiáticos (Moreau & Coomes, 2006), esto causa una reducción drástica de sus poblaciones naturales (Olivares et al, 2013). Ambas especies comparten características de su historia de vida que las hacen vulnerables a la sobreexplotación como la madurez tardía, baja fecundidad y cuidado parental bucal paterno (Duponchelle et al, 2012). En la Amazonía peruana, el sacrificio de machos adultos, sumado a un limitado monitoreo y deficiente control de su comercialización, ponen en peligro las poblaciones naturales de esta especie (Moreau & Coomes, 2006;Da Silva et al, 2009).…”