FISHERIES SCIENCE 2006; 72: 705–709 Blackwell Publishing AsiaMelbourne, AustraliaFISFisheries Science0919 92682006 Blackwell Publishing Asia Pty LtdAugust 2006724705709Original Article Role of free neuromasts in larval feeding Y Mukai *Corresponding author: Tel: 60-8832-0000. Fax: 60-8832-0261. Email: mukai9166@yahoo.co.jp Received 4 July 2005. Accepted 22 December 2005. Role of free neuromasts in larval feeding of willow shiner Gnathopogon elongatus caerulescens Teleostei, Cyprinidae Yukinori MUKAI* Borneo Marine Research Institute, Universiti Malaysia Sabah, Locked Bag 2073, 88999 Kota Kinabalu, Sabah, Malaysia ABSTRACT: It has been reported that the larvae of willow shiner Gnathopogon elongatus caerule- scens have many free neuromasts on their body surface. This study examined the ability of the willow shiner larvae to feed on zooplankton by mechanoreception by the free neuromasts. Feeding exper- iments using untreated larvae and larvae treated with streptomycin, which impairs free neuromast function, were conducted under light and completely dark conditions. The larvae were put into Petri dishes, then nauplii of Artemia salina were introduced. The average number of Artemia eaten by the larvae was expressed as the average ingestion rate of Artemia/10 min. The ingestion rate of Artemia for untreated larvae was 12.3 under light conditions and 10.6 Artemia/10 min. even in complete dark- ness. The ingestion rate in the larvae treated with streptomycin was 11 under light conditions and only 0.8 Artemia/10 min under dark conditions. The low rate in the treated larvae under dark conditions must be due to impairment by the streptomycin. Therefore, the high ingestion rate for the untreated lar- vae under dark conditions would be surely dependent on mechanoreception. The results indicate that larval willow shiner is able to feed on zooplankton under limited light conditions. KEY WORDS: feeding behavior, free neuromasts, Gnathopogon elongatus caerulescens, larvae, willow shiner. INTRODUCTION Lateral lines of fish, in general, develop from free neuromasts on the body surface, which are known to play a complementary role to vision in feed- ing. 1–3 In certain species or under limited condi- tions, free neuromasts play an important role in detecting prey; for example, larvae of mottled sculpin Cottus bairdi can feed on Artemia in the dark by using free neuromasts. 4 Artificially blinded surface-feeding Aplocheilus lineatus can also detect insects on the water surface using free neuromasts. 5–8 The willow shiner Gnathopogon elongatus caer- ulescens (Teleostei, Cyprinidae), an important spe- cies in fisheries, inhabits calm lakes and feeds on zooplanktonic prey. 9 The larvae of this species show a high sensitivity to minute water displace- ments, since they have many free neuromasts with longer cupulae compared with other cyprinid fish at the early larval stage. 10 Therefore, the willow shiner is suitable for the study of the function of free neuromasts. 11 In our previous work it was reported that willow shiner larvae can eat zoop- lankton in complete darkness. 12 Here the role of free neuromasts in the feeding of willow shiner lar- vae is examined in comparison with the role of vision. MATERIALS AND METHODS Feeding experiments Eggs fertilized by artificial insemination of the willow shiner Gnathopogon elongatus caerulescens were provided by the Shiga Prefecture Fisheries Experimental Station. The larvae were reared in 60- L glass aquariums with the water temperature kept at 16–20°C. Larvae were fed an artificial diet and Artemia salina nauplii. Larvae that were 21–33 days old after hatching and 7.8–12.8 mm total length were used for feeding