New Report of Zu cristatus (Bonelli, 1819) in the Ionian Sea with an In-Depth Morphometrical Comparison with All Mediterranean Records

Monitoring the occurrence and distribution of rare fish species is essential, especially in a semi-closed basin such as the Mediterranean Sea. Biologically interesting species often represent fishing waste (being part of the by-catch) and therefore are not retained, leading to a huge gap in data collection. Here we report about the occurrence in the Ionian Sea of a Zu cristatus (Bonelli, 1819) specimen, a mesopelagic fish from the order Lampriformes considered rare in the whole Mediterranean basin. The sample was captured at a depth of 720 m off the coast of Noto (Sicily, Italy) by deep-sea longline fisheries. The biometrics and meristic data were compared with all the available data on specimens previously reported in the Mediterranean Sea. It is interesting to note that, among the few records in the literature, most reports mention a lower depth range for this species. In fact, it is quite known that juvenile specimens of Z. cristatus were frequently found in shallow waters, while information about the biology of the adult stage is scarce, indicating they would seem to prefer much deeper environments. Considering the difficulty to collect data on this rare fish, this contribution can help to improve the knowledge about its distribution.