Sexual maturation and larval development of the immigrant Asian date mussel, Musculista senhousia, in a Po River deltaic lagoon

Abstract

The reproductive cycle of the non‐indigenous mytilid Musculista senhousia was studied over a one‐year period in the Sacca di Goro, a lagoon in the Po River deltaic area, where the species was recently accidentally introduced. Four main stages were recognized: gonad spent, developing, ripe, and spawning. Oocytes in previtellogenesis appeared in March and coexisted with growing oocytes. Spermatogenesis preceded oogenesis, and sperm clusters were observed from May. Yolk‐filled eggs were present from June, but, instead of being spawned, underwent summer degeneration. Conversely, spawning started in mid‐September, coinciding with water temperature decrease, and lasted to November, after which the gonads were spent. The species is strictly gono‐choric. Both the cohort‐of‐the‐year and the survivors of the co‐hort‐of‐the‐previous‐year started maturation. Such an overlap of reproducing generations is probably an adaptation for survival in a variable environment. The reproductive output of M. senhousia was determined following stimulation trials using hydrogen peroxide. Emission of gametes was completed within 4 h, and a single female might release as many as 137.103 egg cells. Swimming D‐shaped larvae APPEARED within 24 h of fertilization. Larval life had a duration of approximately 15–18 days.