Age structure, growth and survival rates of the commercial fish Prochilodus nigricans (bocachico) in North-eastern Ecuador

Abstract

The bocachico, Prochilodus nigricans, is a commercially important fish distributed throughout the central and western Amazon. Age and growth of this species in eastern Ecuador were determined by otolith and scale increment analyses. For otolith analyses, we used thin sections of the astericus, and clear visualization of annuli required the use transmitted polarized light. Accuracy and precision of age estimation were compared to select the best ageing structure. Precision indices showed that otoliths are more reliable than scales to determine the age of bocachicos. Based on marginal increments analysis, we found that annulus formation in both structures occurs once a year between August and December. Seasonal changes in growth were associated with hydrological cycle of the river. The Ecuadorian Prochilodus at the juvenile-adult stage grew faster (i.e., K = 0.29 for ages 2 and older) than conspecific populations from Bolivia and Brazil (K = 0.5). In addition, annual mortality rate (A = 0. 56) was lower than reported for Prochilodus populations elsewhere in the Amazon. We conclude that this population is presently not overexploited, but conservation and management schemes for this population will need to consider that it is an international, trans-boundary migrant.

Reproduction, feeding and migration patterns of Prochilodus nigricans (Characiformes: Prochilodontidae) in northeastern Ecuador

“…Dispersal of a fish species may depend on diverse life stages and the context of geomorphology and habitat heterogeneity in a given river basin (Duque et al, 1998). This analysis complements available information on ecology of P. nigricans in eastern Ecuador (Silva, Stewart, 2006), relating their migratory, reproductive and feeding behaviors to seasonal flooding dynamics. Migratory fishes with important nutritional and commercial value are highly susceptible to anthropogenic perturbations (e.g., Allen et al, 2005).…”

“…2). This short-lived fish is a fast-growing species (Silva, Stewart, 2006) with: 1) delayed maturation, 2) moderate to large adult size, 3) high fecundity, 4) short annual spawning season, 5) absence of parental care, and 6) long-distance migrations to productive, wetseason floodplains, all of which ensures rapid replacement of the stock. These traits correspond to a seasonal strategy of neotropical fishes that takes advantage of both temporal and spatial variation in quality of habitats for enhanced juvenile survival and growth (Winemiller, 1989).…”

“…These observations are like those described by Laraque et al (2007) and Saul (1975). Detailed environmental observations and aquatic habitats of the region were thoroughly described in Ibarra, Stewart (1989), Galacatos et al (1996Galacatos et al ( , 2004, Silva, Stewart (2006) and Laraque et al (2007).…”

“…Numbers above bars indicate average size at each age estimated from otolith data (Silva, Stewart, 2006).…”

“…The smallest male and female at gonadal stages IV and V during April measured 225 and 283 mm SL, respectively. These sizes correspond to age classes 2 and 3, respectively, as estimated from a von Bertalanffy growth model based on otolith data (Silva, Stewart, 2006). Empirical estimates of mean length at sexual maturity could not be made because of the relatively low number of fish caught in the high-waters of the spawning season.…”