Vertebrate fauna of SE Asia
  

 

   
 
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Text and photos by Nick Baker, unless otherwise credited.
Copyright ゥ Ecology Asia 2022

 
 
     
   
   

 

   
   
 
Crocodile Longtom
   
   

Fig 1
   

Fig 2
 

Fig 3
 

Fig 4
  

 

 

 

 

 

 

Order : Beloniformes
Family : BELONIDAE
Species : Tylosurus crocodylus
Maximum Length : 150 cm

The genus Tylosurus comprises, as of 2022, ten recognised species of 'longtom', also known as needlefish or houndfish. According to Fishbase, four of these occur in the waters of Southeast Asia.

Tylosurus crocodylus (Crocodile Longtom or Hound Needlefish) is one of the larger species of the genus, potentially reaching a maximum length of around 150 cm and a maximum weight of 6.4 kg (see Fishbase). Its range extends throughout the tropics, in the waters of the Atlantic, Indian and Pacific oceans. It is associated with coral reefs and coastal lagoons.

The example shown here was identified as a type of Tylosurus based on the length of the jaws (somewhat shorter than those of the genus Strongylura), and more specifically the presence of a dark, fleshy, lateral keel on the side of its caudal peduncle (the caudal peduncle is the point at which the tail fin joins the body).

In Tylosurus crocodylus the body colour is greenish or bluish-green above, and silvery beneath, and the lower lobe of the tail fin is markedly longer than the upper.

This is a fast-moving, mainly solitary predator; its long, streamlined, muscular body has evolved to rapidly accelerate towards its selected prey, which are typically slower-moving fish. The sharp, pointed jaws, armed with sharp teeth, and sudden bursts of speed can be hazardous to fishermen wading in shallow waters.


Fig 1 : Crocodile Longtom, photographed at night using camera flash; this example, found in a boating marina on Sentosa, one of Singapore's southern islands, had an estimated total length of around 50 cm.

Fig 2 : Singapore's southern islands, as viewed from Sentosa Island; these include Tekukor Island with St. John's Island behind, and in the far distance the hills of Batam Island (Indonesia). These relatively calm, shallow waters support a population of Crocodile Longtom.

Fig 3 : Close-ups of the head, showing the moderately long jaws lined with sharp teeth.

Fig 4 : Close-up of the tail. The small, dark mark on the caudal peduncle is the lateral keel, which identifies this fish as a Tylosurus.



Thanks to Kelvin Lim for identifying this fish.


References : F3

Links :
Fishbase