História natural do “peixe de areia”, Awaous tajasica (Lichtenstein, 1822) (Teleostei: Gobiidae) no Baixo São Francisco, Nordeste do Brasil

Abstract

The natural history helps to generate important information for species conservation. This study aimed to know the natural history, with an emphasis on diet and the period of activity (Chapter I), reproduction and sexual dimorphism (Chapter II) Awaous tajasica (Gobiidae) in the São Francisco River. Samples were collected between the months of October 2013 and August 2014. In Chapter I were carried out underwater observations through snorkeling and collecting specimens and sediment for a year to diet, and for a day at intervals of four hours to assess the period of activity. The diet used the IAi and Ivlev index, and the period of activity used the RI. The observations recorded up defense behaviors and those related to supply. The observations were registered defensive behaviors and those related to diet. In the diet (n = 199) were found 23 items, grouped into animal materials (AM), vegetable (VM) and (OM) others. There AM increase with the increase in size and to decrease the VM. The Ivlev index indicated preference for bivalves, gastropodas and insect larvae, as were avoided: nematode, nemertea, scales and microplastic. Regular excavations during foraging A. tajasica fit better as rooter. The follower behavior was recorded, and A. tajasica nuclear was 4 species of fish followers. The morphology of the digestive tract indicates a preference for VM, however the items in the content suggests omnivorism, generalist in its breadth and opportunistic seasonally, with preference on a seasonal basis by VM (December and February) and AM (April and June). The Ivlev suggests preference for invertebrates, which shows visual guidance in the search for food. The RI and observations suggest two corroborating activity peaks suspicious of other studies. Chapter II sought to characterize and define the sexual dimorphism and reproductive period of A. tajasica in San Francisco river. Samples were taken at 4 points, a total of 361 especimens. They were measured 12 morphometric variables in each individual. The reproductive cycle was determined by the variation of gonadosomatic indices (GSI) (n = 101) and determined the size of sexual maturity (L50). Only the jaw length was significant, where males are larger than females, which is common to gobys with parental care. The value of L50 was 59 mm CT for females. The sex ratio was significant in total, and only every two months: February, April and August. The phases of maturity and the GSI suggested that the reproductive period takes place in the warm months (October to April), with a peak in February. In June it suggests the post-spawning period. There is a fishing gobys larvae in various locations around the world, however there is his record in Baixo São Francisco, but it takes attention, as there shrimp fishing that may be capturing gobys as escorts. Thus fishing may interrupt the life cycle of A. tajasica.