ARTICLE 134    2015


by Jenny Edwards


When some fish are stranded on the beach, all that is left after a few days are some bones.  This is not the case with boxfish which dry out to mummified versions of their former selves. 
One Nature Coast Marine Group member and her visitors have collected quite a few of these tropical boxfish from Jemison’s Beach, south of Potato Point.  Perhaps you know of other hotspots for finding them.
The larger fish in the photo was a Round-belly Cowfish (Lactoria diaphana).  You can see why it got the name cowfish from the pair of “horns” and even in the dried fish its underside is quite curved.  When alive the fish is yellowish to brown with dusky spots and blotches. Juveniles have an almost transparent lower portion to their body which is why this species is sometimes called the Transparent or Translucent Cowfish or Boxfish.
Round-belly Cowfish are tropical fish usually inhabiting seaweed covered reefs and adults can reach 30cm in length. The juveniles drift for great distances and have been found as far south as eastern Tasmania. 
The two smaller fish in the photo are Humpback Turretfish (Tetrosomus gibbosus).  They have at least 13 other common names but my favourite is the Hovercraft Boxfish.   They are another tropical species and are quite common in sheltered bays and estuaries where the bottom is covered with weed or seagrass.  They feed on invertebrates and worms and can grow to 30cm.  Occasionally juveniles turn up in Victoria.
In both cowfish and turretfish the body is almost completely covered with hexagonal bony plates  that are fused into a “case”.  There are holes for the animal’s moving parts such as fins, gills eyes and mouth.  Larger Humpback Turretfish have dark outlines to the plates with blue spots in the centre of each.
Species in the boxfish family (Ostraciidae) are slow swimmers but protect themselves with a layer of toxic slime that can also be released when the fish is stressed.  Aquarium owners are warned that the toxin will pollute the water and can kill everything in their tank.


Round-belly Cowfish and two Humpback Turretfish


Photo - Rachel McInnes