I've checked.

The Blue Whale is the biggest fish or should I say mammal in the sea by far. About 110ft in length.

The Blue Whale (Balaenoptera musculus) is a marine mammal belonging to the suborder of baleen whales (called Mysticeti).[3] At up to 33 metres (110 ft) in length and 181 metric tonnes (200 short tons) or more in weight, it is believed to be the largest animal to have ever lived.

Whale Shark comes in 2nd I guess.

The largest specimen regarded as accurately recorded was caught on November 11, 1947, near the island of Baba, not far from Karachi, Pakistan. It was 12.65 metres (41.50 ft) long, weighed more than 21.5 tonnes (47,300 lb), and had a girth of 7 metres (23.0 ft).[5] Stories exist of vastly larger specimens—quoted lengths of 18 metres (59 ft) are not uncommon in the popular shark literature—but no scientific records exist to support their existence. In 1868 the Irish natural scientist E. Perceval Wright spent time in the Seychelles, during which he managed to obtain several small whale shark specimens, but claimed to have observed specimens in excess of 15 metres (49.2 ft), and tells of reports of specimens surpassing 21 metres (68.9 ft).

In a 1925 publication, Hugh M. Smith describes a huge whale shark caught in a bamboo fish trap in Thailand in 1919. The shark was too heavy to pull ashore, but Smith estimated that the shark was at least 17 metres (56 ft) long, and weighed approximately 37 tonnes (81,500 lb), which have been exaggerated to an accurate measurement of 17.98 metres (58.99 ft) and weight 43 tonnes in recent years. There have even been claims of whale sharks of up to 23 metres (75 ft). In 1934 a ship named the Maurguani came across a whale shark in the Southern Pacific ocean, rammed it, and the shark consequently became stuck on the prow of the ship, supposedly with 4.6 metres (15.1 ft) on one side and 12.2 metres (40.0 ft) on the other.[6] No reliable documentation exists of those claims and they remain little more than "fish-stories".

Lazy to read? Well, basically it says that there are claims of the Whale Shark being up to 75ft long which is about 23 metres. The largest specimen accurately recorded was about 41ft which is about 12 metres.

So there ya go Mr Az. I did my research and thus have proven my findings. Sources are from wikipedia.com.

Chao.