Induced reproduction and cryopreservation of the semen of the Southern kingcroaker Menticirrhus americanus (Perciformes: Sciaenidae)
The Southern kingcroaker Menticirrhus americanus is a Sciaenidae with wide distribution on the west coast of the Atlantic, from Argentina to the USA In view of its potential for aquaculture, the objectives of the present study were captive breeding and cryopreservation of M. americanus semen. For the induction of final maturation and egg production, the study tested the effectiveness of human chorionic gonadotropin (hCG), following through histology the effects on the development and maturation of oocytes. In males, sperm quality was tested after cooling and cryopreservation of semen in dimethyl sulfoxide (DMSO). The development of oocytes was classified into pre-vitellogenesis, vitelogenesis and maturation. In the porridge, the beginning of vitelogenesis is marked by the formation of lipid globules and cortical alveoli in the periphery of the ovoplasm.Protein vitelogenesis is characterized by the formation of calf granules and coalescence of lipid globules. The coalescence of the calf forming a single mass, together with the hydration of the oocytes, marks the end of maturation. Induced females (300 IU hCG.kg-1) showed 60% success in spawning, with a latency period of 38.1 ± 3.4h. The eggs measured 730 ± 0.06 μm in diameter, with fertilization and hatching rates of 63.8 ± 14.5 and 43.3 ± 10.7%, respectively. Relative fertility was estimated between 40,080 and 294,000 eggs.kg-1. In dosages of 300, 600 and 900UI of hCG.kg-1 the success in spawning was 45, 60 and 41%, respectively. The three dosages induced the final maturation of the oocytes, but the best reproductive performance was at 600 IU hCG.kg-1 with the highest fertilization rate (73%) and the highest estimated larvae production (39.000/spawning). The semen showed osmolality of 370 mOsm.kg-1, spermatocrit of 88%, pH 6.9 and density of 9.9 x 109 sperm.mL-1. Sperm motility was activated from 300 mOsm.kg-1. The motility tests, after refrigeration (5 ̊C) were performed at 3 h intervals and demonstrated that the extruded semen maintains the quality for 15 h, but if maintained in the testis this period is 6 h. In cryopreservation tests, DMSO 5, 10 and 20% concentrations did not impair sperm motility or post-thaw membrane integrity, indicating 5% DMSO for semen cryopreservation. In summary, the results of this study allowed to outline efficient protocols for the final maturation of oocytes and cryopreservation of semen, proving, for the first time, the possibility of reproducing Menticirrhus americanus in captivity. At the same time, the data presented here should serve as an initial basis for future studies necessary to optimize the production of larvae of this species.