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.

Detritivorous fishes form an important part of the ichthyomass in the Amazon basin. Most of these fishes are contained in the orders Characiformes and Siluriformes (catfishes). The Characiformes constitute more than 30% of the total fish yield in the Amazon basin, whereas the catfishes are of minor importance. Stable isotope data indicate that Characiformes species receive most of their carbon through food chains originating with phytoplankton, while the Siluriformes receive a significant part of their energy from other plant sources.

Abstract.— The present study investigated the use of benzocaine as an anesthetic for juvenile Colossoma macropomum (tambaqui). In the first experiment, fish were exposed to various doses of benzocaine for 10 min at 24 C. The second experiment examined the effects of duration of exposure to 100 mg/L of benzocaine. In the third experiment, fish were exposed to 100 mg/L at temperatures of 24, 27, and 30 C. Benzocaine concentrations of 100–150 mg/L were considered ideal for quickly inducing total immobilization and fast recovery. Fish exposed to 350 mg/L benzocaine exhibited 30% mortality. No changes in hemat‐ocrit were recorded in fish exposed to different concentrations of benzocaine. Plasma glucose increased significantly when fish were exposed to benzocaine concentrations greater than 200 mg/L. Recovery time after a 30‐min exposure to 100 mg/L benzocaine was significantly greater than after an exposure for 10 and 20 min. No mortality was observed 96 h after exposure to 100 mg/L benzocaine for 10, 20, and 30 min. Dosages in the 100–150 mg/L range were effective for periods of up to 20 min of anesthesia. There was no effect of temperature on the time required for fish to lose equilibrium. However, recovery was significantly faster for fish anesthetized at 30 C. Benzocaine is an effective anesthetic agent for tambaqui juveniles, providing rapid immobilization and rapid recovery. Benzocaine is also less expensive than other available anesthetic compounds.

The increased demand for juvenile tambaqui Colossoma macropomum for grow‐out ponds and stocking programs in the Amazon state of Brazil has increased the transportation of this species. This study was designed to determine the optimum density of juvenile tambaqui during transportation in closed containers. Fish (51.9 ± 3.3 g and 14.9 ± 0.4 cm) were packed in sealed plastic bags and transported for 10 h at four densities: 78, 156, 234, and 312 kg/m3. After transportation, fish from each density were kept in separate 500‐L tanks for 96 h. Mortality, 96‐h cumulative mortality, water quality, and blood parameters (hematocrit, plasma cortisol, and glucose) were monitored. Fish mortality after transportation was significantly lower at densities of 78 and 156 kg/m3 than at 234 and 312 kg/m3. Cumulative mortality was significantly lower at a density of 78 kg/m3. Dissolved oxygen after 10 h of transportation remained high at a density of 78 kg/m3, but reached critically low values at all other densities. Ammonia concentration was highest at the lowest density and was lower at higher densities. Carbon dioxide concentration was lowest at the density of 78 kg/m3 but higher in the other treatments. Plasma glucose and cortisol increased significantly immediately after transportation at densities of 156, 234, and 312 kg/m3, returning to control values by 24 h. The best density for juvenile tambaqui during a 10‐h transportation haul in a closed container was 78 kg/m3. At this density there was no fish mortality, water quality was kept within acceptable values, and fish were not stressed.

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