Population density, growth and reproduction of arapaima in an Amazonian river‐floodplain

Abstract

Arantes CC, Castello L, Stewart DJ, Cetra M, Queiroz HL. Population density, growth and reproduction of arapaima in an Amazonian river‐floodplain. Ecology of Freshwater Fish 2010: 19: 455–465. © 2010 John Wiley & Sons A/S Abstract – Compensatory density effects are key features of fish population dynamics that remain poorly understood in tropical river‐floodplains. We investigated possible compensatory growth and reproductive processes for a river‐floodplain population of Arapaima sp., an extinction‐prone fish species of South America. Body growth was studied through analysis of ring patterns on the scales, and size and age at sexual maturity was studied through analysis of female gonads. Growth and maturity were compared for unmanaged conditions with relatively low population density (in 1990s) versus managed conditions with markedly higher density (in 2005–2006); between 1999 and 2005–2006, abundance increased 7.3 fold. Results contradict theoretical expectations for slower growth and delayed reproduction at higher population density. Total lengths of arapaima at low population density were significantly shorter for age classes 1–5 compared with lengths of those age classes at high population density (ancova, P < 0.0001 for both slopes and intercepts). Total length at 50% maturity (L50) only declined about 4% with increasing density (e.g., 164 cm at low density vs. 157 cm at high density). Apparent faster growth at high density and only a slight change in size at maturity resulted in fishes spawning at an earlier age with high density conditions (age 3 vs. age 4–5). We hypothesise that these patterns reflect compliance with minimum size limits of catch during the high density (managed) situation, where there was no harvest of immature fishes. Compliance with minimum size limits, thus, may have led to faster average body growth rate and earlier reproduction, which has greatly promoted population recovery.

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

“…Silva, Stewart (2006) concluded that black prochilodus in Ecuador form annuli on their otoliths, with the first annulus forming at a SL of about 180 mm (Fig. 2), while others have suggested that black prochilodus and various other fishes in the Central Amazon appear to form bi-annuli on their scales (e.g., Oliveira, 1997 ;Arantes et al, 2010). More research is needed to determine the causes and possible regional variations in translucent zone formation in this and related taxa.…”

Trophic ecology of Arapaima in Guyana: giant omnivores in Neotropical floodplains

“…Community-based management programs and protected areas have been effective in facilitating recovery of depleted populations in some areas (Castello et al, 2009;. Recent studies on growth (Arantes et al, 2010), nesting (Castello, 2008a), and migration (Castello, 2008b) also have contributed information necessary for effective conservation and management of Arapaima. For Guyana and many areas of the Amazon basin, however, there are few or no published observations on trophic ecology of Arapaima, and there are few published studies on stable isotope ratios in Arapaima (Forsberg et al, 1993, present only δ…”

“…Our results taken as a whole (i.e., isotope values, morphology and diets) suggest that Guyanese Arapaima are more appropriately considered omnivores rather than top predators. That does not take away from their role as consumers in Neotropical ecosystems, however, because their rapid growth (Arantes et al, 2010), large adult size, and relatively low trophic level may allow them to attain very high biomass. It also is evident that there are more than one species of Arapaima in the Amazon River basin (Stewart, 2013, in press), so further studies may reveal that some species are trophic specialists, Arantes, Nov. 2006).…”

Evidence of polygamy in the socially monogamous Amazonian fish Arapaima gigas (Schinz, 1822) (Osteoglossiformes, Arapaimidae)

“…Imbiriba (2001) reports that the arapaima's reproduction is probably related with the water-level variation on the floodplains of the Amazon River. Sexual maturity occurs around the third to fifth year of life, when the fish reach an average length of 1.6 m and weigh 40 -50 Kg (Lüling, 1964;Godinho et al, 2005;Arantes et al, 2010). Fontenele (1953) observed that during the spawning season secondary extragenital sexual characteristics develop in the breeders, such as that males begin to present a dark coloring on the upper part of the head and flanks, and the abdomen and caudal peduncle turn reddish.…”

“…Even though it has been exploited commercially for many years, much basic life history data are still lacking. However, several recent publications have made significant advances of our understanding of growth and reproductive behavior (Arantes et al, 2010), population dynamics (Coutinho et al, 2010;Castello et al, 2011), spatial and temporal distribution and trophic ecology (Watson et al, 2013) as well as population structuring (Hrbek et al, 2005;Hrbek et al, 2007;Araripe et al, 2013).…”