Comparison of ovarian functions for keeping embryos by measurement of dissolved oxygen concentrations in ovaries of copulatory and non-copulatory oviparous fishes and viviparous fishes

Abstract

To investigate causes of anomalous development of embryos facultatively fertilized in the ovary of a non-copulatory oviparous fish Hemilepidotus gilberti (Scorpaeniformes: Cottdae), dissolved oxygen (DO) concentrations were measured in ovaries of copulatory oviparous ( Alcichthys alcicornis, Bero elegans), non-copulatory oviparous ( H. gilberti, Hexagrammus otakii), and viviparous ( Sebastes taczanowskii, Zoarces elongatus) fishes. DO concentrations changed during vitellogenesis and ovulation cycles, and also before and after ovulation. DO concentrations in the ovary of H. gilberti and H. otakii at ovulation were 0.27±0.03 and 0.15±0.03 mg O 2 l −1, respectively, whereas in A. alcicornis and B. elegans, the concentrations were 0.47±0.08 and 0.20±0.06 mg O 2 l −1, respectively. In the ovaries of intralumenal gestation viviparous fishes, S. taczanowskii and Z. elongatus, DO concentration was from 0.01 to 0.11 mg O 2 l −1. The average DO concentration during the artificial pregnancy of A. alcicornis was 0.97±0.19 mg O 2 l −1, but all embryos showed deformity. DO concentrations recorded in oviparous fishes in this study were lower than the oxygen level at which most oviparous fish embryos exhibit retardation or death, and it probably caused the anomalous embryonic development. In contrast, the normal development of viviparous fish embryos at low oxygen level was attributed to the specialized structure of ovary, e.g. the dual arterial system to supply the developing embryos with the respiratory demands in Sebastes.