Distribution

A. Indian Ocean, Red Sea, western Pacific;
B. Coastal regions ranging from Japan and the Philippines to eastern Australia;

C. Indian Ocean, Red Sea, Pacific Ocean;

D. Rivers and brackish water in Singapore, Sumatra, Borneo and New Guinea;

E. Indian Ocean, Red Sea, Pacific Ocean;
F. Coastal regions and brackish water from the Persian Gulf to western India;

G: 1. Nicobar and Solomon Islands; 
     2. Coastal waters of the mainland and larger islands from eastern India to Australia and China;
     3. Gulf of Suez and Gulf of Aqaba in the Red Sea, coastal waters of Saudi Arabia;

     4. Western Central Pacific, Indonesia.

     5. Indian Ocean and western Pacific from the Red Sea and eastern Africa eastward to Tahiti and from Japan southward to Australia;
H. Coastal waters (sometimes also brackish water) from western India to China, southward to the Malay Archipelago.


Fig. 4.29 Synanceia horrida

Biology

Well-camouflaged, bottom-dwelling fish found in shallow water, poor swimmers. Often half buried in sand or mud or between stones or stands of coral, they are practically invisible to prey and enemies alike. Fish that swim close by can be sucked into their mouths through a lightning-quick motion.

Stonefishes in the strict sense belong to the genus Synanceia. They are counted among the most dangerous venomous fish, and the two large and widespread species S. verrucosa and S. horrida in particular can lead to cases of severe envenoming. Despite their dangerousness, they are caught as edible fish in some regions of the eastern Pacific. Larger specimens can grow to around 40 cm or more and can reach a weight of up to more than 1.5 kg.

Compact, compressed body with a high back. Warty, tough and scaleless skin with loose flaps and algae growing on it. This makes their outline indistinct and the fish are perfectly camouflaged against the surrounding substrate. Mouth and eyes directed upwards; the eyes may even protrude above the outline of the head. The 13 most anterior dorsal spines are massive, with grooves on both sides and each with 2 large venom glands. The venom spines are covered with a sturdy integument (Fig. 4.20). 3 rays on the anal fin and 2 on the ventral fin also function as venom spines, although it is virtually impossible for envenoming to be caused by these spines, as they are unlikely to be employed since these fish are strictly bottom-dwellers. Moreover, they are covered in such a thick integument that it would be practically impossible for them to function as venom apparatuses.

Envenoming generally occurs as a result of these well-disguised animals being trodden upon. The dorsal spines are often only erected at the last moment. As a result, the integument and venom glands are pushed downward as the spines enter the skin, and under this pressure, the venom glands discharge their contents along the grooves on the spine and into the wound. As the venom glands do not extend as far as the tip of the spine, depending on the size of the fish, the spine must enter to a sufficient depth for the glands to be compressed in order for envenoming to occur. In smaller animals, that may be the case at a depth of ½ cm, while in larger fish, it may be 1 cm or more.

The other genera mentioned above tend to be uncommon fish, and little is known about their biology. The body of Erosa spp. is similarly compact and stout as in Synanceia. Leptosynanceia, Pseudosynaceia and Trachycephalus have a more elongated form. Venom spines and glands are not as massive as in Synanceia.

Risk

Contrary to their bad reputation, fatal envenoming due to S. verrucosa and S. horrida is rare, and only isolated fatalities have been described. The circumstances of the deaths in these patients, however, are poorly documented.

Most injuries occur when these fish are trodden upon (beware – at low tide Stonefishes may be exposed above the surface of the water), less frequently due to inadvertently touching the fish under water or careless handling of dead fish. Among other factors, the severity of envenoming depends on:

1. the size of the animal: larger fish have larger venom glands, but in smaller animals venom is squeezed out even when the spine does not penetrate deeply (see above);
2. the number of venom spines that penetrate the skin (usually barely more than 2–3);
3. the amount of venom injected, which to a certain extent correlates with the depth of penetration.

Intensive, radiating pain that may become intolerable within minutes after the sting. Because of the risk of drowning, it is important to leave the water as soon as possible after a Stonefish sting. Trainers or sandshoes only offer limited protection, as thin soles can be easily penetrated.

Literature (biological)

Cameron 1988, Endean 1961, Eschmeyer and Rama Rao 1973, Grobeker 1983, Halstead et al. 1956, Halstead 1988, Lagraulet et al. 1972, Smith and Heemstra 1986, Sutherland 1983, Williamson et al. 1996

Catalogue of life