Largest fish ever

Modern estimates suggest that the largest fish ever to live on Earth was the now-extinct predatory shark known as megalodon (Otodus megalodon; formerly Carcharodon megalodon) which is believed to have reached at least 15–18 m (50–59 ft) and perhaps up to 20 m (65 ft) long. Its mouth could have gaped as much as 2 m (6 ft 6 in) wide. It lived in Earth's oceans (particularly warmer waters) during the Early Miocene to the Pliocene, between 23 and 3.6 million years ago.

Megalodon means "big tooth". The longest megalodon tooth found to date was about the same length as a TV remote.

Previously thought to be related to the great white shark (Carcharodon carcharias) – which is today's largest predatory fish – it has now been designated into its own family, Otodontidae. The two last shared a common ancestor some 60 million years ago. As a size comparison, megalodons reached around three times the size of the largest ever documented great white.

The upper size limit for megalodon has long been debated ever since its first fossilized teeth were found in the early 1800s; earlier estimates of lengths up to 30 m (98 ft) are now known to have been in error. For many decades, a range of 15–18 m (50–59 ft) has been accepted as the threshold, but a new method of extrapolating body size from its teeth – one of the few remaining remnants we have of these giant sharks because their cartilaginous bodies do not fossilize – by tooth width as opposed to length pushed their body length range up to 20 m (65 ft). This new method was devised by palaeontologist Victor Perez, while a doctoral student at the Florida Museum of Natural History (now of the Calvert Marine Museum in Maryland, USA).

The largest extant fish overall is the filter-feeding whale shark (Rhincodon typus), which grows on average to 4–12 m (13–39 ft) long, though one female specimen caught in the Arabian Sea off Veraval in Gujarat, India, on 8 May 2001 measured a reported 18.8 m (61 ft 8 in).

The biggest bony fish ever known (as opposed to cartilaginous fish such as sharks) is a specimen of the marine fossil species Leedsichthys problematicus. Dating back c. 165 million years, it is estimated to have reached up to 16.76 m (55 ft) in length. It had previously been thought to have been far longer, but this was downsized after new findings announced by University of Bristol palaeontologist Jeff Liston in August 2013 at the 61st annual Symposium on Vertebrate Palaeontology and Comparative Anatomy in Edinburgh, UK.