Apart from the two species featured here, a third species of fish, the crescent oyster blenny (Omobranchus smithi) has also been found locally in timber in the mangrove (Lim, 2017). While the whitebar oyster blenny (Omobranchus ferox) is known to be common in the mangroves of Singapore (Lim & Low, 2002: 132), the crescent and zebra oyster blennies appear to be rare. Omobranchus zebra was described from Singapore in 1868 (Bleeker, 1868: 279 as Petroskirtes zebra). One recent record in the country (Toh et al., 2016: 92) is based on two specimens of 36.4 and 25.5 mm standard length (ZRC 47516) obtained from among fouling organisms under floating pontoons at the Raffles Marina, at Tuas, in 2000. The dark vertical bands on its head readily distinguish Omobranchus zebra from its two congeners in Singapore mangroves. Omobranchus ferox has a distinct narrow white bar behind its eye, and Omobranchus smithi has a black crescent-shaped mark dorsally at the rear edge of its eye (Springer & Gomon, 1975 - Omobranchus smithi as Omobranchus meniscus). Oyster blennies of the genus Omobranchus are not the only fish known to hide in timber crevices. At the mangroves of the Tukang Besi Archipelago in Sulawesi, Indonesia, the dartfish, Parioglossus interruptus, was discovered taking refuge in dead wood riddled with tunnels made by shipworms (a type of boring mollusc of the family Teredinidae) exposed during low tide and at night, apparently to evade predators (Hendy et al. 2013). It is believed that protection from the heat and the retention of sufficient water in the wood help the fish survive in the wood during low tide. Note: The authors wish to thank the National Parks Board for permission to conduct research in the mangroves on Pulau Ubin.

Opinions and declarations Rendered by the International Commission on Zoological Nomenclature

The blue bronzeback is one of six species of Dendrelaphis recorded from Singapore. It appears to be locally uncommon, and is distinguished from the similar looking elegant bronzeback (Dendrelaphis formosus) by the blue skin between the scales on the neck and the absence of three black lines on the posterior part of the body (Baker & Lim, 2012). When alarmed, this species is known to inflate the anterior part of its body, revealing the metallic blue coloration on each side (Grismer, 2011)

This appears to be the first documented sighting of the locally uncommon blue bronzeback at Venus Loop. Despite the rather degraded forest in this area, it acts as a buffer zone to the MacRitchie forest. It is interesting to note that many forest specific animals have been recorded in this area, including the blue bronzeback’s congeneric relative, the Haas’s bronzeback (Dendrelaphis haasi), which has been seen there on at least two occasions (see Sankar & Ng, 2016).

The blue Malayan coral snake feeds on other snakes which it subdues with its potent venom. The present observation and a previous encounter by Xu & Teo (2013) appear to suggest that the predator does not let go of its victim once it has bitten. It probably waits for the prey to die before commencing to swallow it

In Singapore, this snake appears to inhabit forest, and recorded mainly from the Bukit Timah and Central Catchment Nature Reserves (Baker & Lim, 2012: 113). Although known to be terrestrial and semiaquatic (see e.g. David & Vogel, 1996: 124), the featured sighting shows that it can be partially arboreal. This species is now known to be venomous. Subaraj (2008) gives an account of the effects suffered from its bite.

The blue-tailed dartfish was first recorded from Singapore waters in November 2011. It has been observed to hover at approximately 30 cm to 1 m off the sandy bottom, and is known to share burrows with an unidentified species of alpheid shrimp and the ventral-barred shrimp-goby, Cryptocentrus sericus (see Jaafar & Ng, 2012: 369). Such an interaction in Singapore waters had not been illustrated previously The dartfish is not regarded as an obligate symbiont of alpheid shrimps as the shrimp-gobies are. It only uses the burrow as a retreat and does not maintain physical contact with the shrimps that excavate the burrow. As the resident shrimps and gobies tolerate its occupancy by not evicting it, it is conceivable that the dartfish does contribute to the safety of the burrow’s residents. By hovering high above the burrow’s entrance, it is able to detect danger farther than can be seen by the shrimp-goby, and with its retreat, issue an advance warning to the burrow’s occupants. The present observation, however, does not appear to support the above suggestion. Despite the dartfish’s disappearance into the burrow, both the burrow’s occupants (the pistol shrimp and the shrimp-goby) still maintained their presence at the burrow’s entrance. It is possible that the dartfish and the shrimp-goby each have their own interpretation of potential threats, and the distance with which intruders are tolerated vary between dartfish and shrimp-goby. This may explain why the shrimp-goby did not respond to the reaction of the dartfish. Thus, it seems that the shrimp-goby does not depend on the dartfish’s apparent early warning.