The effect of supplemental feeds with different levels of crude protein on pond water quality and food utilization efficiency by pacú (Piaractus mesopotamicus) was evaluated in a semi‐intensive culture system. Fish were stocked at a density of one individual per m2, raised for 299 days, and fed isocaloric diets containing soybean meal, blood and bone meal, and yellow maize. Dietary treatments consisted of diets containing 25%, 35%, and 45% crude protein. Ponds receiving the two highest protein levels showed significantly higher values of alkalinity, conductivity and nitrites. High dietary protein diets resulted in no significant improvements in final weight (336.4±77.2, 308.2±92.6 and 368.4±82.2 g, mean±standard deviation, for 25%, 35% and 45% protein levels respectively). Moreover, fish carcass composition was not significantly different among treatments. Instead, significant augmentations in feed conversion ratio (1.36, 1.54 and 1.73 respectively) and reductions in protein retention (35.7%, 33.5% and 29.0% respectively) occurred as protein levels increased. Results indicate that at the lowest protein level, pacú growth rates and carcass composition were similar to the other experimental treatments, with a significant improvement in pond water quality and feed utilization efficiency.

SUMMARYTitan broiler chickens kept in batteries at the Universidad Agraria, Lima, were fed diets containing duckweed (Lemna gibba) in proportions of 0, 10, 15 and 25%. The weight gain of broilers fed 15% duckweed was similar to that of the controls; 25% duckweed in the diet resulted in a significant decrease in feed consumption and weight gain.To determine if Titan and Arbor Acres broiler chickens could be maintained on duckweed diets under commercial conditions, birds were fed diets containing 0 and 5% duckweed. Female birds (Titan and Arbor Acres) fed diets containing 5 % duckweed showed increased final weights. The pigmentation of all birds receiving the diet containing duckweed was significantly increased.Duckweed used at levels of up to 15 % in the diets of broiler chickens could represent an important protein source for poultry feed in developing countries where soyabean meal or fish-meal are not available.

~~ ___ ~-The growth of broiler chickens on diets containing various levels of Lemna gibba was evaluated. Groups of broiler chicks were fed on diets containing 0-400 g Lemna gibbalkg for 3 weeks. These chickens were then changed to standard diets for a further 2 weeks. As the level of Lemna gibba increased, feed consumption and weight gain decreased. However, when diets were changed to the standard diet, compensatory growth was observed. In a second experiment, diets were formulated with a metabolizable energy of 5.02 MJ (1200 kcal)/kg Lemna gibba and included a finer-milled Lemna gibba. Chickens were fed on diets containing 0-300 g Lemna gibbalkg for 4 weeks. Each group was then divided into two subgroups. For the next 2 weeks one of these sub-groups was maintained on the experimental (Lemna gibba) diets (LL), while the other sub-group was changed to a standard diet (LS). Bird fed at levels above 150 g Lemna gibbalkg had decreased consumption and weight gain. These birds when changed to a standard diet tended to have increased weight gain compared with chickens continuously fed standard rations. LS birds had significantly higher weight gains and feed consumption and lower feed conversion than LL birds. In contrast to older birds, chicks fed on Lemna gibba a t high concentrations showed growth retardation. When changed back to a standard diet they demonstrated normal or compensatory growth.

Four valid species are currently recognized in the Neotropical migratory genus Salminus: Salminus brasiliensis, Salminus franciscanus, Salminus hilarii and Salminus affinis. However, molecular evidence strongly suggested that two different species might be contained under the taxonomic denomination Salminus brasiliensis. Therefore, the geographical distribution of each entity was evaluated in order to understand their contribution to the different stocks of major river networks in South America. Major river networks of the La Plata River basin were explored to characterize the geographical distribution of the two genetic lineages. To characterize further the genetic partitioning within each lineage of S. brasiliensis, a haplotype analysis was conducted. The 5′ region of the mitochondrial COI gene was used as the molecular marker. In total, 45 fish samples of S. brasiliensis from 19 sites in Argentina, Brazil and Paraguay were sequenced. Additional COI sequences of S. brasiliensis, S. franciscanus and S. hilarii were gathered from public databases. All samples of S. brasiliensis comprised two different mitochondrial lineages. Accordingly, phylogenetic tree topologies segregated the complete set of sequences into two disparate clusters. One of these clusters was far closer phylogenetically to S. hilarii than to other S. brasiliensis. While one of the genetic lineages of S. brasiliensis seemed mostly restricted to the upper Paraná River, the other showed a widespread distribution along major river networks of the basin. Fifteen unique haplotypes were identified and collapsed. Salminus hilarii and S. franciscanus have private haplotypes. In S. brasiliensis, each mitochondrial lineage also hosts a set of unshared haplotypes. The sympatry of two different putative species within S. brasiliensis together with their unshared haplotypes present a difficult situation for management and conservation that calls for timely solutions.