Yukinori Mukai

Ontogenetic eye development and related behavioural changes in larvae and juveniles of barramundi Lates calcarifer (Bloch)

Larvae and juveniles of barramundi Lates calcarifer (Bloch) were examined for the development of the retina, occurrence of the retinomotor response and retinal tapetum and change in eye size with age in days. The barramundi hatched with unpigmented non-functional eyes in which retinal cells had not yet differentiated into the various elements. Soon it was followed by rapid changes in the histology of the retina. Two-day-old larvae had a well-pigmented retina with area temporalis which would allow acute vision and prey attack in the nasal direction. At 10 days, rod cells and the retinal tapetum first appeared in the retina and the retinomotor response first occurred; these would allow feeding in dim light. The retinal tapetum moved in unison with the cones and the pigment epithelium during the retinomotor response. At 26 days, the horizontal cells were divided into two layers and the twin cones appeared. These changes in the eyes occurred concurrently or in anticipation of behavioural changes, such as the onset of the first feeding at 2 days, the shift of habitat from coastal waters to swamps at the notochord flexion stage at 7–15 days, the abrupt change in feeding behaviour from roving zooplanktivore to lurking predator at 25–30 days and a later shift of habitat from turbid swamps to open coastal or lake areas at the early juvenile stage.

Morphogenesis of sense organs and behavioural changes in larvae of the brown-marbled grouper Epinephelus fuscoguttatus (Forsskål)

The morphogenesis of sense organs and related behavioural changes in the hatchery-reared brown-marbled grouper Epinephelus fuscoguttatus larvae were examined to gain better understanding of its early life history because ecological field observations for grouper species is difficult. The newly hatched larvae (2.1 mm total length) had developing eyes and otic vesicles, a pair of free neuromast on the head and ciliated olfactory epithelium. At 3 days post hatching (dph), the eyes became fully pigmented with pure-cone retinae, the semicircular canals formed in the inner ear, and the larvae (2.8 mm) were able to swim horizontally, preying on rotifers. Retinal rods and the intra-oral taste buds at pharyngeal appeared next. The olfactory lamellae and the head lateral line system then formed, and the inner ears developed completely in the larvae during the metamorphosis period (15–40 dph; 5.1–18.1 mm). At settlement (50 dph; 32.8 mm), the fish possessed taste buds in the mouth entrance region, and the lateral line system developed completely. The sensory development correlates well with the known aspects of its life history at sea whereby the larvae can feed early and avoid predators during the passive drift, are able to swim shoreward to search nursery ground along the metamorphosis stage and survive in seagrass beds at settlement.

Morphogenesis of free neuromasts in the larvae of brown-marbled grouper Epinephelus fuscoguttatus

Abstract Newly hatched larvae had one pair of free neuromasts behind the eyes. As the larvae grew, free neuromasts increased in number. The apical surface of sensory epithelium widened and subsequently elongated. The number of sensory hair cells increased and the directions of maximum sensitivity became both anteroposterior and dorsoventral on the trunk. Before notochord flexion, only the anteroposterior type was observed. After notochord flexion, two types of neuromasts were observed on the trunk. On the head, the orientation of free neuromasts formed a tangential line to concentric circles around the eyes and nostrils. Free neuromasts on the head could therefore receive stimuli from various angles from predators or zooplanktons. This suggests that these free neuromasts play a role in compensating for a dead angle of vision, and an important role in detecting zooplankton under scotopic vision. Canal organs were observed on the head and operculum in 40-d-old animals.

Coral recruitment success and sessile benthic colonisation estimation in Tioman Island Marine Park, Malaysia

This study examined the implementation of designated artificial reef plates made of coral rubble, sand and plasters cement as a potential substrate in order to optimise the recruitment success at four reef sites in Tioman Island in Malaysia, namely Genting Village, Renggis Island, Teduh Bay and Juara Bay between April 2012 and June 2013. Recruitment was dominated by Acroporidae (65.48%), followed by Pocilloporidae (31.4%), Faviidae (2.34%), Poritidae (0.89%) and Fungiidae (0.19%). Terracotta tiles had significantly higher recruitment densities compared to artificial reef plates, and were further compared to artificial reef plates at each reef site (Mann Whitney Uxa0=xa0983.5, Zxa0=xa0−3.43, ρxa0<xa00.05) during the initial settlement period. However, no significant difference was observed between both types of plates during the post-settlement period. Artificial reef plates exhibited a higher mean total benthic percentage cover compared to terracotta tiles during both settlement periods. These results might provide significant information on a proper substrate in order to optimise coral settlement.