Trout coelomic fluid suitability as Goldfish oocyte extender can be determined by a simple turbidity test

Regeneration technologies such as androgenesis, intracytoplasmic sperm injection, and nuclear transfer require that handling conditions do not alter oocyte ability to sustain embryo development. One important parameter in the maintenance of oocyte quality in fish is the possibility to prevent oocytes activation during manipulation. In Cyprinid, such activation is known to be delayed when Salmonid coelomic fluid is used as incubation medium. Coelomic fluid however is a biological fluid whose ability to sustain oocyte quality during in vitro incubation may be variable. The purpose of the present work was to explore this variability using Rainbow Trout (Oncorhynchus mykiss) coelomic fluid (TCF) and Goldfish (Carassius auratus) oocytes, and to set up a test which would reflect TCF suitability for Goldfish oocyte incubation. We showed that different TCF induced very different development rates after oocyte incubation for 30 min at 20 °C: at 24h post fertilization (pf) and at hatching, rates ranged between 35% and 110% of the non-incubated controls. When TCF (1 volume) was mixed with tap water (9 volumes), a precipitate developed whose extent was measured by spectrophotometry. This turbidity test proved to be highly correlated to development rates after Goldfish oocyte incubation in TCF (r(2) = 0.83 at hatching, n = 150): TCF with the highest turbidity (> 1.5 absorbance unit at 400 nm) were the ones which altered the most the development rates after incubation (less than 50 % at hatching). This easy and rapid turbidity test can therefore be used as a reliable estimator of TCF suitability for Goldfish oocyte incubation and manipulation.