More effective induction of spawning with long-acting GnRH agonist in the shi drum, Umbrina cirrosa L. (Sciaenidae, Teleostei), a valuable candidate for Mediterranean mariculture

Abstract

Three experiments of spawning induction in shi drum, Umbrina cirrosa L., were performed in six different commercial Italian hatcheries from May to August (water temperatures: 19–29 °C; salinity: 21–37 p.p.t.). In the first experiment, 119 females (1–4.7 kg), subdivided into 29 lots, were injected with a single dose (2, 5, 8, 10, 15 and 20 μg kg−1 body weight) of short-acting gonadotropin- releasing hormone agonist (GnRHa-S), des-Gly10,[D-Ala6]-LH-RH ethylamide. In the other two experiments, 85 females (0.7–5.8 kg), subdivided into 22 and four lots, were treated with one (40 or 80 μg kg−1) or three doses (40 μg kg−1) of long-acting GnRHa (GnRHa-L), respectively. GnRHa-S stimulated spawning in 69% of the 29 treated lots; the number of eggs laid reached a maximum of 130 000 and a weighted mean of 29 200 total eggs kg−1. GnRHa-L elicited a spawning response in 95% of the 22 one-dose treated lots; the number of laid eggs was higher than with GnRHa-S, reaching a maximum of 213 100 and a weighted mean of 59 400 total eggs kg−1. The yield of developing embryos in 67% of the single GnRHa-L treatments was higher (sometimes up to three times) than with GnRHa-S. Triple treatments of the four lots of females with GnRHa-L always resulted in spawning responses; the best result corresponded to a number of total laid eggs of 358 900 eggs kg−1 with a yield of 177 300 developing embryos.