Biology of the subtropical sac-spawning euphausiid Nyctiphanes simplex in the northwestern seas of Mexico: Interbrood period, gonad development, and lipid content

Abstract Interbrood period, gonad development, and total lipid content throughout the oogenesis and spermatogenesis processes of the subtropical euphausiid Nyctiphanes simplex were studied. Specimens were collected during six oceanographic cruises in Bahia Magdalena (March, July, and December 2004) and in the Gulf of California (November 2005 and January and July 2007). Females attained first spawning when ∼7.5 mm total length (>52 days old). Histological evidence indicates that N. simplex females have group-synchronous ovaries, able to produce four broods per gonadic cycle, since ovigerous females develop simultaneously in three and four distinct substages (Oc1, Oc2, Oc3, and Oc4) in their gonads. Once females mature, as shown by pale pink gonads, they may reabsorb their gonads in 10 days. Embryonic development in the ovigerous sac last Nyctiphanes , Nematoscelis , and Pseudeuphausia are numerically dominant euphausiids in several highly eutrophic temperate, subtropical, and tropical ecosystems. N. simplex males have a continuous spermatogenesis after they attain size at first maturity; continuously allocating ∼5.4% of weight-specific carbon to reproduction, results that are significantly different than previous assumptions that euphausiid male spermatogenesis is energetically insignificant.