An important step towards the domestication of pirarucu Arapaima gigas , the largest of Brazil's native fish, was given by the researcher from Embrapa Fisheries and Aquaculture , Lucas Simon Torati: the discovery of hormones, proteins, peptides and likely pheromones in the liquid secreted by the head of adult animals.
The scientist analyzes the hypothesis that the fry directly benefit from such secretion due to its biochemical composition. The research identified more than proteins secreted by the fish. The discovery was published in the scientific journal Plos One. In his PhD thesis defended at the University of Stirling , in Scotland, Torati was able to demonstrate that such secretion contains sexual steroids possibly used as pheromones, hormones that cause attraction for mating.
The scientist observed that whenever the level of such hormones was high in blood samples, it was also high in the head's secretion. Such unprecedented revelation proved the unique nature of pirarucu. Generally speaking, fish release pheromones through semen or urine, but in no other species their presence was identified in head liquid.
The research also verified that the mucus has proteins that can benefit the fry, which would be one of the causes that would justify the constant presence of younglings over the top of the head of the fish. Several hypotheses had been raised, such as that the fry feed from this liquid, a sort of lactation.
The partnership allowed the scientist to monitor the sexual steroids of 20 couples. Researcher Lucas Toratti talks about the substances secreted by pirarucu and their likely functions. The research also advanced in the study of the relationship between the secretion and parental care, addressed by the paper in Plos One. It was the first time the presence of protein and peptides was identified in such mucus, which, according to Lucas Torati, despite its reduced amount, could benefit the fry, since there are several proteins in adult pirarucus' immunological system.
