Hub for Marine Life: Saw Fish (Pristis microdon)

**SAW FISH(Pristis microdon)**

Kingdom:Animalia

Phylum:Chordata

Class:Chondrichthyes

Subclass:Elasmobranchii

Order:Pristiformes

Family:Pristidae

Genus:Pristis

Species:P.microdon

Author:Latham 1794

The fish is known for its long saw like snout, high value fin and meat. They are most critically endangered species of shark belonging to the family Pristidae. Saw fishes are distributed in tropical areas of Indo-West Pacific region. Since, it has saw like snout it is commonly called as large tooth saw fish. It is characterized by long tapering snout with 14-22 large teeth on both sides. Space between last teeth is twice less than space between first teeth. Average size of these sharks is 5meters and it weighs about 600kg. The dorsal side of the fish is greenish grey or golden brown and creamy white in the ventral side. The pectoral fins are high and angular whereas dorsal fin is located in front of pelvic fin. They live in shallow water region with sandy or muddy bottom. Adults are found in seas and estuaries, but the juveniles are found in the rivers. The long snout with sharp teeth is a deadly weapon used for attacking the prey and also for self defence. Like most sharks it is also ovoviviparous, where the young ones develop inside the female body.

Feeding mechanism

Most of the elasmobranches with elongated snout don’t use their snout for sensing and capturing their prey. But Pristis microdon uses its snout to sense the electric fields of the prey and catches its prey. It uses its three sensory modalities (Vision, electron reception, mechanoreception) for feeding. The snout of pristid saw fish is compared with extinct sclerorhynchids saw fish. The extinct sclerorhynchids saw fish has functional teeth and dormant replacement teeth and P. Microdon’s saw consist of lateral teeth formed from baseline and lengthen snout with slimmer construction. This adaptation helps them to enter into a school of fish and swipe its saw laterally to injure the fishes. It easily catches those injured fishes which is separated from their school and feeds on them. It also uses it saw to cut the whales and sieve the sandy substratum to capture the buried prey. The dense distribution of photoreceptors shows several peaks mediating acute vision in Pristis microdon. Electron reception of pristids is higher than the rhinobatids shovel nose rays. Ampullae of lorenzini pores are present more in number, which helps to locate the prey easily.

Threats

Goa, India

Used as religious symbol at Taiwan temples

All species of this shark are listed as “critically endangered” in IUCN(International Union for Conservation of Nature) red list. The reason for dwindling of the shark population is due to; increasing fishing activity as a result of high economic value of fin and meat. Since, all the species have elongated snout they get easily entangled in the fishing nets. They are highly susceptible to gill nets and have all possibilities of getting entangled. According to the report of discovery news (Discovery’s shark week Aug 4-10) these sharks are routinely killed and their meats are sold in the market. Sadly, the snout is also taken as a souvenir for display. In India it is protected under the wild life protection act.