Morphometrics, ovary structure, and parasites of Chiasmodon harteli (Actinopterygii: Trachiniformes: Chiasmodontidae) from off south-eastern Greenland

Abstract

Background. Chiasmodon harteli Melo, 2009 is a rarely captured deepwater fish. Even though the taxonomy of this genus is fairly well resolved, very little is known about the biology of individual Chiasmodon species. The objective of the presently reported study was to supplement new knowledge on C. harteli. Materials and methods. A single female specimen of C. harteli was captured on 1 July 2008 off the south-eastern coast of Greenland during bottom trawling at the depth of 1000 m. Morphometric and meristic data were collected and absolute values of the measurements [to the nearest 0.1 mm] were also related to the fish standard length and head length. To determine the gonad maturity stage, ovaries were fixed in Bouin’s solution and buffered formalin (4%), dehydrated, embedded in paraffin wax, cut into 5-μm histological sections and finally stained with haematoxylin and eosin. Parasitological examinations covered the skin, eyes, mouth, nasal cavities, gills, gonads, spleen, gastrointestinal tract, liver, kidneys, peritoneum, and muscles. Parasites recovered were preserved in 70% ethanol. Results. Detailed morphometrics, including metric and meristic characters, as well as dentition formula, are provided. The individual studied was a mature female. The ovaries were in stage I  (Merson scale) (mature, featuring oocytes in early vitellogenesis and oogonies). The mean oocyte cell diameter was 84.62 ± 4.67 µm, while the range: 45.05–114.08 µm. The fish hosted only one parasite species—Anisakis simplex (Nematoda; encysted L3 larvae). The stomach of the specimen studied was enlarged, although completely empty. Conclusion. This is the first substantiated record of this species since its original description in 2009. The structure of female gonads of C. harteli was described here for the first time. The acquired data on the gonadal development may shed new light on the species’ reproduction and may help to approximate the spawning time. The nematode A. simplex were reported herein for the first time in a Chiasmodon.

Keywords

• swallower
• morphometrics
• gonads
• Anisakis simplex