Fish

Barred Hamlet (Hypoplectrus puella)
Barred Hamlet (Hypoplectrus puella)

Causes of colour patterns in coral reef fish

The hamlets, a group of reef fishes from the wider Caribbean, sport a stunning array of colours and patterns, but the genetic basis of this morphological variety is unclear.

Although the hamlet lineage is about 26 million years old, the diversification of colours appears to have occurred only within the last 10,000 generations in a burst of diversification that ranks among the fastest in fishes.

Some of the nests that were discovered
Some of the nests that were discovered

World's largest fish breeding area discovered in Antarctica

Using a towed camera system, researchers discovered the world’s largest fish breeding area near the Filchner Ice Shelf, south of the Antarctic Weddell Sea.

The nests belonged to the Jonah’s icefish (Neopagetopsis ionah). Mapping the area suggested a total extent of 240 square kilometres. Based on the density of the nests and the size of the breeding area, it was estimated that there were about 60 million nests.

Snowflake morays can capture prey on land

Many of us are familiar with photos of moray eels snug in their caves or crevices, peering out into the open sea.

One might imagine them venturing out to hunt for prey when hunger pangs strike or an unfortunate prey swims by, but do you know that a particular species of moray eels—the snowflake moray—can hunt on dry land as well?

At least, this was what happened when a group of scientists from UC Santa Cruz filmed snowflake morays emerging out from the water onto dry land, then grabbing a piece of meat with their fangs, and swallowing it.

Sulphur mollies move in waves in response to the presence of a predator.
Sulphur mollies move in waves in response to the presence of a predator.

Sulphur mollies move in waves to evade predators

While fish are generally no match for predatory birds that hunt them from above, the sulphur molly, a freshwater fish species which can grow up to 4.5 inches, appear to have developed an effective defence mechanism.

When the school spots a potential predator (not necessarily birds, but any other species that may prove a threat, including humans), the school start swimming in waves that were conspicuous, repetitive and rhythmic.

And it is not just a few hundred sulphur mollies involved in this display—we're talking about a much larger number. 

Anemonefish sheltering in coral
Anemonefish sheltering in coral

Chemical pollutants disrupt reproduction in anemonefish

Thanks to increased awareness, we are all aware of how some plastic food utensils can leach Bisphenol-A (BPA) into our food.

BPA is an endocrine disruptor and it can interfere with how the hormones in our bodies function. Studies have shown that pollutants like BPA tend to feminize animals like freshwater fish, rats and mice. 

How does it affect animals whose gender is determined by its environment? 

Why do fish rub themselves against a shark?

Fish rubbing themselves against a shark's body may sound as if they have a death wish, but this is precisely what some fish have been spotted doing. And it turns out that such behaviour is more widespread and frequent than one would think.

A study led by the University of Miami (UM) Shark Research and Conservation Program at the Rosenstiel School of Marine and Atmospheric Science uncovered over 40 instances of fish rubbing themselves against a shark’s skin in over ten locations around the globe.

While chafing has been well documented between fish and inanimate objects, such as sand or rocky substrate, this shark-chaffing phenomenon appears to be the only scenario in nature where prey actively seek out and rub up against a predator.

A short-snouted seahorse in the Red Sea.
A short-snouted seahorse in the Red Sea.

Seahorses—slow swimmers, swift hunters

Seahorses appear to be slow passive hunters as they use their tail to cling to coral or seaweed. However, this can be deceiving, as they are swift, efficient hunters. 

A recent study by Tel Aviv University, published in the Journal of Experimental Biology, documents the speed at they hunt. 

Three species of seahorses with varying snout lengths were chosen for the study: Jayakar's seahorses, sea ponies and short-snouted seahorses. 

Chromis viridis (green chromis) is a species of damselfish.

Fish trust friends in a crisis

In social animals living in the wild, individuals rely on their buddies to alert them if a predator is lurking.

All animals aim to balance the risk of predation against the energy investment necessary to execute an escape, to maximise the number of correct reactions (e.g. reacting to the presence of a predator) and minimise reactions to inaccurate information (e.g. reacting to harmless stimuli).

Trust among individuals is critical. This is true for humans as well as many other species, including fishes.

Study co-author Jacob Johansen, Ph.D.

Researchers studied more than 200 marine fish species before coming up with their findings.
Researchers studied more than 200 marine fish species before coming up with their findings.

Baby reef fishes take the gold

A study has shown that baby reef fishes clock in at 15 to 40 body lengths per second, making them one of the fastest youngsters around.

In contrast, baby herring swim up to two body lengths per second, while the fastest human (Olympic gold medallist Michael Phelps) manages just 1.4 body lengths per second.

So how did those tiny baby reef fishes get to be so fast so early in their lives?