Parasite collection, measurements & electron microscopy

Selected parasites of silver kob (Argyrosomus inodorus) (Actinopterygii: Sciaenidae) from northern Namibia

A total of 55 silver kob were collected over 11 months (June 2017, and August 2017 to May 2018), with 5 fish sampled and examined each month. Of these, 49 silver kob were caught using conventional angling gear at Toscanini and Mile 108, both sites within the Skeleton Coast Park, at about 20°50’S, 13°25’E and 21°49’S, 13°25’E, respectively (Figure 1). Six silver kob were caught by local anglers in Henties Bay (22.1°S and 14.3°E) (Figure 1).

Fish were sacrificed by a single cut through the spinal cord. The skin, fins, eyes and gastrointestinal organs were examined for parasites according to the procedure of Noga32. All parasites were identified and counted. In total, 28 species were identified33, but for the present study only 5 species are listed and described. Whole mount preparations were made for monogeneans using glycerine ammonium picrate solution on microscope slides and some were preserved in vials with 70% ethanol. Nail varnish was used to seal the whole mounts.

Photomicrographs, drawings and measurements of parasites were made using a camera lucida and calibrated eyepiece of an Olympus (BX50) compound microscope or a Zeiss (Discovery V8) camera calibrated on a Leica dissecting microscope. All measurements are in micrometres (µm) unless otherwise indicated. In the descriptions, the initial number is the mean measurement followed by the minimum and maximum measurements (range) in parentheses and finally the number of specimens measured for that particular category (n=x).

For scanning electron microscopy, specimens were dehydrated through a series of ethanol (70, 80, 90, 100, and 100%) for 1 h each, followed by immersion in hexamethyldisilazane. After complete evaporation of hexamethyldisilazane, the specimens were sputter coated with gold–palladium in a Polaron SC7640 sputter coater. Specimens were then kept in a fume cupboard so that no dust fell on them while waiting for evaporation of hexamethyldisilazane. The specimens were examined using a LEO VP 1540 microscope at 10 kV.

Article TitleSelected parasites of silver kob (Argyrosomus inodorus) (Actinopterygii: Sciaenidae) from northern Namibia

Published
January 27, 2022
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Abstract

The present study reports five metazoan parasites recorded from silver kob (Argyrosomus inodorus). Five fish were collected monthly (n=55) for 11 months in 2017–2018 (excluding July 2017) using conventional angling gear in Toscanini, Mile 108 and Henties Bay, northern Namibia. Fish were examined individually for ecto- and endo-parasites. Photomicrographs, drawings and measurements of parasites were made using a camera lucida and calibrated eyepiece of an Olympus (BX50) compound microscope and/or a Zeiss (Discovery V8) camera calibrated on a Leica dissecting microscope. Amongst species found, monogeneans including Diplectanum sciaenae van Beneden & Hesse, 1863, two species of Calceostoma van Beneden, 1858, one species of Sciaenacotyle Mamaev, 1989 and one acanthocephalan Corynosoma australe Johnston, 1937 were found and are reported here. This is the first study of parasites found from silver kob of the Atlantic Ocean. Silver kob has potential to be used as a mariculture species. In addition to mariculture, information obtained from this study may also be used as a baseline for stock structure and biological tagging.


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