Shyncronization of the hatching time of the silverside Odontesthes bonariensis (Teleostei:Atherinopsidae) through temperature, salinity, and oxygen stimuli

The silverside, Odontesthes bonariensis, shows an extended hatching period, from the 15th to the 19th day after fertilization at 15°C, what is undesirable for bioassay tests and larviculture purposes, since it is important to obtain the maximum number of larvae emerging on the same day. In order to try a shyncronization of the hatching period, seven tests plus a control were performed, including temperature (+3° C), salinity (+5º/oo), and dissolved oxygen (-1 mLO2.l-¹) shocks, either individualy or in combination. Mature silverside were collected in the field and the eggs were artificially fertilized; in the laboratory they were incubated under controlled temperature (15 ± 0.5° C), salinity (5 ± 1¹/oo), and photoperiod (12L:12D); the oxygen was kept at saturation level (6.79 mlO2.l-¹). The tests were initiated when the first larvae began to hatch (15 days after the fertilization). The control groups showed an average hatching of 38%, while eggs subjected to temperature shocks showed the best hatching performance, averaging 86%. The lowest result was observed with the salinity shock treatment, where only 14% of the larvae hatched during the 24h period. Based on these results, it is recommended a temperature shock (3°C rise) to obtain at least 80% of the O. bonariensis larvae hatching on a single day.