Introduction

The genus Peniculus von Nordmann, 1832 belongs to the family Pennellidae Burmeister, 1835 and contains 14 nominal species (Boxshall and Halsey 2004). Pennellids are highly transformed, often elongated copepods parasitic on marine fishes and cetaceans (Kabata 1979). Some of pennellids are ectoparasitic (e.g. Exopenna Boxshall, 1986; Parinia Kazachenko & Avdeev, 1977) but many are deeply inserted into the body of their host. The insertion can take place in the gills, the skin or in the musculature of the host without any particular preference, as is the case for the genus Pennella Oken, 1816 (Kabata 1981; Boxshall 1986).

Two species of Peniculus are redescribed from Korea in this study. They are Peniculus minuticaudae Shiino, 1956 and Peniculus truncatus Shiino, 1956. In Asia, nine species of Peniculus have so far been reported including six from India and three from Japan. The species reported from Japan are Peniculus minuticaudae, Peniculus truncatus and Peniculus ostraciontis Yamaguti, 1939 (Shiino 1956, 1959; Yamaguti 1939, 1963). One of these three pennellids, Peniculus ostraciontis, was redescribed from Korea by Choi et al. (1996) but we reveal here that theirs was a misidentification of Peniculus truncatus.

Shiino (1956) described Peniculus minuticaudae based on females collected from the fins of threadsail filefish Stephanolepis cirrhifer (Temminck and Schlegel, 1850) (= Monacanthus cirrhifer), from Shirahama, Wakayama Prefecture, Japan. Recently, infection of Peniculus minuticaudae on two cultured fish hosts, Stephanolepis cirrhifer and the black scraper Thamnaconus modestus (Günther, 1877), was reported from Oita Prefecture, Japan (Nagasawa et al. 2011), after Fukuda (1999) reported the same species from the same locality as an unidentified Peniculus sp.

Peniculus truncatus was also identified and described by Shiino (1956) based on a single female found on the fin ray of oblong rockfish Sebastes oblongus Günther (1877) [= Sebastichthys mitsukurii] collected off Wagu, Mie Prefecture, Japan. A third species, Peniculus ostraciontis, was described based on females collected from the head of Humpback turretfish Tetrosomus gibbosus (Linnaeus, 1758) [= Ostracion gibbosum] on the Pacific coast of Japan (Yamaguti 1939). It was reported again from the triangular boxfish Tetrosomus concatenatus (Bloch, 1785) [= Rhinesomus concatenatus] from Sagami Bay by Shiino (1959) (Table 1). All three Peniculus species are in need of redescription and here we undertake the redescription of two of them.

The host Tetrosomus modestus have been cultured at a few localities along the southern coastal regions of Korea. At Tongyeong marine living resources research & conservation center (TMRC), several commercially important fishes were ranched under the marine ranching program in Korea by Korea Institute of Ocean Science & Technology (KIOST) from 1998 (MOMAF 2007). Recently, we studied the symbiotic organisms associated with ranched fishes and their life cycles at TMRC (Venmathi Maran et al. 2012). The black scraper is one of the fishes that have been transferred into cages for the purpose of experimentally studying its feeding activities within this marine ranching program. The second host, Stephanolepis cirrhifer, is uncommon in culture in Korea because of its small size and low growth rate, in contrast to Japan (Fukuda 1999). The Korean rockfish Sebastes schlegelii Hilgendorf, 1880 has been cultured at several localities around the southern coastal region of Korea due to its high commercial value (MOMAF 2007). Despite the increasing threat of parasites in aquaculture, information on parasites and diseases are largely lacking from farmed fishes in Korea. The redescription of Peniculus minuticaudae and Peniculus truncatus is necessary to reveal previously omitted or overlooked features of both species and also to correct the misidentification by Choi et al. (1996) in Korea. In addition, a key is provided for all 14 nominal species of Peniculus.

Materials and methods

The pennellids were carefully removed from the fin rays of the marine ranched Tetrosomus modestus and Stephanolepis schlegelii at TMRC, Tongyeong, Gyeongsangnam-do, Korea (Figure 1) and they were preserved in 70% ethanol. Preserved copepods were cleared in a drop of 85% lactic acid or lactophenol prior to examination using an Olympus BX51 phase contrast microscope. Selected specimens were measured intact using an ocular micrometer and/or dissected and examined according to the wooden slide procedure of Humes and Gooding (1964). Measurements given are the mean followed by the range in parentheses. Drawings were made with the aid of a drawing tube. The descriptive terminology follows Kabata (1979) and the common and scientific names of host fishes follow FishBase (Froese and Pauly 2012). Voucher specimens are deposited at the National Institute of Biological Resources (NIBR), Incheon and Marine Biodiversity Institute of Korea (MABIK), Seocheon, Korea.

Results Order Siphonostomatoida Burmeister, 1835 Family Pennellidae Burmeister, 1835 Genus Peniculus von Nordmann, 1832 Discussion

According to Boxshall and Halsey (2004), there are 14 species on the genus Peniculus: Peniculus asinus Kabata & Wilkes, 1977; Peniculus clavatus (Müller, 1779); Peniculus communis Leigh-Sharpe, 1934; Peniculus elegans Leigh-Sharpe, 1934; Peniculus elongatus Boxshall, 1986; Peniculus fistula Nordmann, 1832; Peniculus furcatus Krøyer, 1863; Peniculus minuticaudae Shiino, 1956; Peniculus ostraciontis Yamaguti, 1939; Peniculus scomberi Gnanamuthu, 1951; Peniculus stromatei Gnanamuthu, 1951; Peniculus theraponi Gnanamuthu, 1951; Peniculus trichuri Gnanamuthu, 1951; and Peniculus truncatus Shiino, 1956.Seven of these are reported from Asian countries.

Alexander (1983) reported Peniculus haemuloni from Brazil, however, it was subsequently treated as a separate genus, Metapeniculus Castro-Romero & Baeza-Kuroki, 1985 based on the presence of only 3 pairs of swimming legs (vs. 4 pairs for Peniculus) (Boxshall, 1986). According to Kabata (1979), two species of Peniculus, Peniculus calamus Nordmann, 1864 and Peniculus fissipes Wilson, 1917 should be regarded as species inquirendae, and in addition we treat Peniculus sciaenae Gnanamuthu, 1951 as species inquirenda since it is also reported with 3 pairs of swimming legs (Gnanamuthu 1951a; Alexander 1983). Thus there are 14 species considered valid and a key is provided for nominal species following Alexander (1983). Most Peniculus species were not described adequately by modern standards and most need to be redescribed. In Asia, all species are poorly described and detailed studies are necessary for the five species reported from India (Gnanamuthu 1951a; 1951b; Pillai 1985) and for the three from Japan (Yamaguti 1939; Shiino 1956).

The mean body length of Peniculus minuticaudae was 2.42 mm. It corresponds well to the body length (2.48 mm) of Peniculus minuticaudae reported from Oita Prefecture, Japan (Nagasawa et al. 2011). The morphological features (Figures 2, 3) agree with the original description of Peniculus minuticaudae (Shiino 1956). The present collection represents the first record of Peniculus minuticaudae from ranched Tetrosomus modestus in Korea. Thus, it is the third documented record of pennellid copepod from commercially cultured fishes.

Peniculus truncatus was originally reported from Stephanolepis oblongus in Japan (Shiino 1956). This parasite is shown here to utilize a second host species, Stephanolepis schlegelii, of the same host genus, although it was initially misidentified as Peniculus ostraciontis by Choi et al. (1996). The misidentification was revealed by comparison between Choi’s descriptions, our material and Yamaguti (1939) illustrations of Peniculus ostraciontis. We collected Peniculus truncatus from the same host species Stephanolepis schlegelii cultured in Korea. The host for Peniculus ostraciontis is Tetrosomus gibbosus (Table 1). In Choi et al. (1996) redescription, they overlooked the third seta on the maxillule and the setules on the maxilla, in addition to the minute setal structures on leg 1.

Peniculus truncatus has so far been reported from two species of the genus Sebastes, Stephanolepis schlegelii and S. oblongus and this pennellid appears to be host specific to rockfish (Table 1). Peniculus minuticaudae and Peniculus ostraciontis might be specific to file fish and puffer hosts, respectively (Yamaguti 1939; Shiino 1956; 1959; Nagasawa et al. 2011; present study). A key is provided for all 14 valid species below.

Key to the species of Peniculus

(Modified from Alexander 1983)

Conflict of interest statement

All authors declare that they do not have any conflict of interest.