The use of attractants in formulated feeds has become paramount to economic success owing to the need to optimize feed conversion rates by maximizing consumption and reducing feed waste so as to lower production costs. Taking into account the importance of attractants, a series of experiments designed to evaluate the potential of natural molecules was carried out with the freshwater prawn, Macrobrachium rosenbergii (De Man, 1879). Two biogenic amines (putrescine and cadaverine) and two sexual pheromones (crab urine and freshwater prawn green gland extracts) were compared with reference products proven to be major attractants, such as squid extracts and a commercial product. These were incorporated in a basal diet designed to be non-attractive. Results were obtained by three different approaches. First, a laboratory bioassay was conducted to evaluate the time that lapsed as an animal presented the different alimentary stages (perception, orientation, movement, arrival and ingestion). A second approach was developed in a commercial farm, to test the performance of the attractants in the presence of other stimuli and in conditions of water movement that may cause rapid dilution. The test consisted of placing a quantity of feed on a tray, which was submerged in a cage (1 m3) in which 10 animals (five males and five females) of 20 g mean weight were placed. The tray was lifted at different times (10, 20, 40 and 80 min) and the number of pellets left was counted. Three replicates were performed for each treatment. A third approach consisted of incorporating an antibody in the feed. Following a methodology similar to the above-mentioned, hepatopancreas and mouth parts of the prawns were collected at different times. Later, immunodiffusion tests were executed to assess the actual ingestion of the feed. The results obtained from the different approaches indicated that cadaverine included at 0.2% was the best attractant. On the other hand, the crab urine and freshwater prawn green gland extracts exhibited good results only with males, so their utilization could be recommended for monosexual cultures.
- Biogenic amines