Ultrasonographic sex determination of the flathead grey mullet (Mugil cephalus)

BACKGROUND: Determination of sex in fish without external sexual dimorphism is important. Sex determination of the flathead grey mullet (Mugil cephalus) in the culture system and spawn‐producing and fish reproduction system is very important. Currently, there are several methods to determine the sex of fish; however, they are time‐consuming, expensive and sometimes dangerous for the fish. OBJECTIVE: The purpose of this study was the sex determination of flathead grey mullet by ultrasonography as a safe and accurate method. METHODS: In this regard, 30 flathead grey mullets (early in their maturation) from a farm in Gomishan‐Golestan province, Iran were examined using a portable ultrasound machine with a 6–12 MHz waterproof linear transducer. Scanning was performed on the ventral body surface in the sagittal and transverse planes, between ventral and anal fins. RESULTS: Differences in shape, qualitative size, echogenicity and the wall layers of the ovary and testis were evaluated for sex determination. Results of ultrasonography were confirmed immediately at necropsy. Ultrasonographic accuracy for sex determination was 100%. The speed of the procedure was around 30 s per fish. CONCLUSIONS: Overall, the sex determination of flathead grey mullet by ultrasonography was high in accuracy and speed, non‐invasive and safe for fish and consumers, and may be considered a priority. Place of the organs in the M. cephalus coelomic cavity and the obtained experience showed that for rapid and easy sex identification, the best place to put the transducer is on the ventral surface of the fish in the caudal part of the coelomic cavity for taking transverse and sagittal ultrasonograms.