First Record of the Cymothoid Isopod Nerocila exocoeti Pillai, 1954 (Crustacea, Isopoda) in the South-West Indian Ocean and First Record of a Perciform Host, Echeneis naucrates, for this Species

PURPOSE

Cymothoid isopods of the genus Nerocila are generally poorly known. The aim of this work was to document the first record of cymothoid isopod Nerocila exocoeti for the South-West Indian Ocean, representing a significant westward range extension for this species.

METHODS

A single adult, female N. exocoeti and 38 mancae specimens were collected from a live sharksucker Echeneis naucrates at D'Arros Island, Seychelles. The female isopod specimen was examined using a stereo microscope and described based on distinct morphological traits. Observations of novel behaviour were also made for E. naucrates.

RESULTS

The examined female isopod specimen measured 26 mm long by 10 mm wide. It possessed short coxae with the postero-lateral angles of pereonites 1-5 not produced and those of 6 and 7 reduced. The first antenna was composed of eight articles and the endopod of the uropod was half the length of the exopod. These traits confirm the specimen as N. exocoeti. Observations of novel behaviour in the wild host specimen showed the individual to deliberately and repeatedly swim ashore before thrashing in the substrate, returning to the water only once the isopod was removed.

CONCLUSION

To date, N. exocoeti is known from India, Indonesia, Papua New Guinea and Taiwan. The present study represents the first record of N. exocoeti from the South-West Indian Ocean region and the first record of E. naucrates as a host of any cymothoid isopod. Additionally, N. exocoeti has previously only been recorded as parasitising beloniform fish hosts and these data present the first evidence of a perciform host for this species. The novel behaviour observed in E. naucrates likely represents a means to remove external parasites.

The behaviour and recovery of juvenile lemon sharks Negaprion brevirostris in response to external accelerometer tag attachment

Behavioural responses of lemon sharks Negaprion brevirostris to a fin-mounted tag package (CEFAS G6A tri-axial accelerometer with epoxied Sonotronics PT4 acoustic transmitter) were measured in a controlled captive environment (n = 10, total length, LT range 80-140 cm) and in free-ranging sharks upon release (n = 7, LT range 100-160 cm). No changes were detected in behaviour (i.e. swimming speed, tailbeat frequency, time spent resting and frequency of chafing) between control and tagged captive shark trials, suggesting that the tag package itself does not alter behaviour. In the free-ranging trials, an initial period of elevated swimming activity was found in all individuals (represented by overall dynamic body acceleration). Negaprion brevirostris, however, appeared to recover quickly, returning to a steady swimming state between 2 and 35 min after release. Post-release tracking found that all sharks swim immediately for the shoreline and remain within 100 m of shore for prolonged periods. Hence, although N. brevirostris are capable of quick adaptation to stressors and demonstrate rapid recovery in terms of activity, tracking data suggest that they may modify their spatial use patterns post release. This research is important in separating deviation in behaviour due to environmental stressors from artefacts caused by experimental techniques.