Did you know that fish get thirsty too? Actually, they might not feel the same sensation of thirstiness that we do, but bony fish (all fish excluding sharks, rays, etc.) in the sea live in an environment in which the concentration of dissolved salts is much greater than inside their bodies.

What this means is that water will have a tendency to move from inside their bodies (lower salt concentration) to outside their bodies (higher salt concentration), particularly via the thin, permeable gill area. To replace water lost this way, marine fish need to drink. Special cells located in their gills extract and excrete excess salt in the sea water the fish take in.

Sharks and their relatives, however, don’t experience this issue to the same degree, due to the presence of organic molecules in their blood that balance out the osmotic gradient between their blood and the sea water, which means sharks may not need to drink as much as other fish in the sea.

Most people have heard of giant squids…deep-sea dwelling cephalopods that are believed to be a primary sources of food for sperm whales, and perhaps the origin of ancient sailors’ yarns about blood-thirsty krakens and sea serpents. Stories of giant squids these days generally refer to a species known as Architeuthis dux, which can grow to an estimated 13 metres in length.

What most people don’t know, however, is that there’s an even bigger squid out there, Mesonychoteuthis hamiltoni, otherwise known as the colossal squid.

First identified in 1925, colossal squids still remain shrouded in mystery. Researchers believe they grow somewhat longer than giant squids but attain much greater mass. With only a handful of specimens to study, it’s difficult to ascertain much more.

The first adult colossal squid caught intact measured 10 metres long and was captured by a New Zealand fisherman in early 2007. One squid scientist commented that calamari rings prepared from the enormous squid would look like tractor tires.

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Remember the movie Alien, featuring the nearly indestructible extraterrestrial with the grotesque set of extra jaws that projected forward to grab and rip prey to shreds? Well, sometimes life is truly stranger than fiction. It turns out that moray eels, some of the most familiar residents of the reef, have a second, hidden set of jaws that they use in a manner highly reminiscent of the voracious monster in the hit sci-fi movie.New high-speed videos captured by researchers at the University of California in Davis show a second set of jaws located deep in the moray eel’s throat lunging out to pull prey in, after the front set of teeth (the ones we normally see) have clamped down on the eel’s next meal.Read more about this fascinating discovery and watch the video here.

Researchers may have discovered the key to synchronised mass coral spawning in an ancient gene that produces primitive light-sensitive pigments known as cryptochromes that developed more than 500 million years ago. These pigments may allow corals to sense moonlight, thus enabling them to coordinate simultaneous spawning across vast distances. Cryptochromes occur in insects, fish and mammals (in people too), so perhaps there’s something to the age-old tradition of romance by moonlight after all? Read more here.

Did you know that some coral reef fish establish a pecking order based on size, and use the threat of punishment to keep other fish in line?

Researchers at James Cook University recently published a study based on analysis of coral goby behaviour at Lizard Island in the Great Barrier Reef. Only the largest male and female gobies in a particular group mate, so gobies living together establish a queue according to size, and wait their turn to reproduce.

There appears to be approximately a 5% difference in size between any particular fish and the one immediately above or below it in the queue. If the size difference drops below this, there may be an ensuing challenge by the smaller fish to jump the queue and move ahead. But if it fails, the larger one may punish the upstart youngster by driving it out of the group…which in coral reef terms, probably means death.

Read more about this fascinating study here

Did you know that clownfish talk to each other? Well, perhaps not exactly “talk” like Nemo in the movie, but they make sounds to communicate among themselves, and maybe to other marine life too. This was demonstrated recently by Eric Parmentier at the University of Liege in Belgium, who is a fish-behaviour specialist.

According to his research, published in the journal Science, Eric and his colleagues determined that clownfish use their jaws to make clicking and knocking sounds…essentially snapping their jaws shut, producing a sound similar to the chattering our teeth make when we shiver.

Perhaps clownfish can’t engage in deep discussions about the meaning of life, but it seems that they’re much more talkative than most of us imagined.

Here’s a sample of clownfish chatter: