Autotrophic Carbon Sources for Fish of the Central Amazon

Abstract

Effective management of the Amazon's commercial fish populations requires an understanding of the factors controlling their production. A fundamental step in the investigation of fish production is to identify the plant groups that contribute energy to fish foodwebs.Stable isotope data for plants and 35 fish species were used to identify autotrophic carbon sources for the central Amazon fish community. Adult fish, aquatic macrophytes, tree parts, periphyton, and phytoplankton were collected in lakes and other flooded environments along the central Amazon floodplain and analyzed for carbon stable isotope composition (o 13 C) by mass spectroscopy. o 13 C values for plants ranged from -39.4 to -11.9o/oo with averages of-33.3, -28.8, -27 .6, -26.2, and -12.8o/oo for phytoplankton, flooded forest trees, C 3 aquatic macrophytes, periphyton, and C macrophytes, respectively. The average for all C 3 plants (phytoplankton, trees, C3 macrophytes, and periphyton) was -29.1o/oo, while the average for C 4 plants (mainly C 4 macrophytes) was -12.8o/oo. Mean o 13 C values for adult fish ranged from -37.0 to -19.8o/oo with an average of-28.8o/oo. Fish and plant data were used in an isotope mixing model to estimate the relative contribution of different plant groups to fish carbon. C 4 macrophytes, which contributed over half of the primary production on the floodplain, accounted on average for only 2.5-17.6% (minimum to maximum) of the carbon in fish. The C 3 plants, as a group, were the primary carbon source for 34 fish species, and accounted for an average of 82.4-97.5% of the carbon in all species. Phytoplankton, a minor C 3 producer, accounted for a minimum of 36.6% of fish carbon on average, and was the principal carbon source for the commercially important characiform detritivores. Several alternative hypotheses are proposed to explain the apparent selective transfer of C 3 carbon through Amazon fish foodchains.

Isotopic variation among Amazonian floodplain woody plants and implications for food-web research

“…Moreover, isotopic ratios of C 3 terrestrial plants usually are assessed from very limited samples of leaves or composite sample of tree parts without consideration of variation within and among species or tissue types within a single plant (e.g., Araujo-Lima et al 1986, Forsberg et al 1993. Very little is known on isotopic variation between vegetative and reproductive tissues, despite the importance of fruit as food for large suites of invertebrates and vertebrates in both temperate and tropical ecosystems (Jordano 2000).…”

Digestibilidade de nutrientes em ração com complexo enzimático para tilápia-do-nilo

“…Nesse sentido, Forsberg et al (1993) afirmaram que as pesquisas devem ser realizadas com combinações diferentes de enzimas puras, isto é, não somente aquelas com ações sinérgicas.…”

Condition factor variations over time and trophic position among four species of Characidae from Amazonian floodplain lakes: effects of an anomalous drought

“…An extreme drought could result in a severe deterioration of the water quality, with high temperature and low dissolved oxygen, which would in turn have negative consequences for the quality of their food sources. For instance, it has been suggested that in addition to feeding on abundant C4 autotrophic sources (Martinelli et al, 1994), Amazonian fish would prefer to exploit C3 sources such as phytoplankton, that are easier to absorb (Forsberg et al, 1993;Mortillaro et al, 2015), but these sources have a tendency to become very scarce during extreme droughts. Both the timing and duration of extreme climatic events are therefore likely to have profound effects on life history strategies of floodplain fish (Ficke et al, 2007).…”