Icefish

poles still rotating
frozen shards traverse the plains
warming bears naught!


During winter in Ottawa, Canada, temperatures plummet well below 0°C. My nose freezes, my fingers freeze, my legs freeze, and my hair freezes. Thankfully my blood never freezes; the red fluid continues to flow throughout my body. I’m an endotherm after all. My body can generate heat internally by, say, digesting the sugar in a toasted marshmallow hot chocolate with whipped cream.

Fishes are not endotherms. Does their blood freeze when the surrounding temperatures drop below zero?

Sort of.

With ice in their blood, icefish happily live in freezing, Antarctic waters (down to −2.0°C). The ice gets into an icefish when it drinks or eats. Wouldn’t you know, icefish have anti-freeze proteins (AFPs) that stop ice crystals in blood from extending and getting larger. But in an unexpected, evolutionary twist, AFPs also prevent ice in blood from melting. Even when waters warm in the summer to temperatures that should theoretically melt the ice in icefish blood, the ice doesn’t melt. How does an icefish survive if ice is accruing in its blood year after year? The answer to this question remains a perciform-ic puzzlement!

P.S. Icy icefish blood is colourless. Colourless blood initially baffled scientists and Dracula alike. Turns out icefishes don’t have hemoglobin – the protein that gives blood its red colouring.

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Nuptial tubercles

his granular crown
powers present, yet eclipsed
fades with summer

Inspiration
Chub (Family Cyprinidae)

Facts
It’s a Friday morning and your 16 year-old self has awoken with a beaming grin – tonight is your first date. With a sprightly skip in your step you start your day. En route to the kitchen you pass the hallway mirror. You abruptly halt all motion. Out of the corner of your eye a shadow rises from your face. You cautiously turn your head toward the mirror. Your stomach instantly begins to writhe – there is a large, angry, pimple on your forehead. Naturally, at 16 this meant disaster.

For some species of fish, bumps on your face are all the rage for first dates. Take for example, freshwater chub of North America.

During the spawning season, male chub guarding nests are known to develop prickly bumps, or nuptial tubercles, on their heads. The structures are made of keratin, the same material your finger and toe nails are made of. Different species can be identified depending on the number, size and pattern of tubercles on their head.

The function of nuptial tubercles is not fully understood. For male creek chub (Semotilus atromaculatus) vying for the loveliest ladies, large head spikes may be useful for fighting off rival males. The menacing “horns” on the swollen heads of bluehead chub (Nocomis leptocephalus) should keep away nest predators.

Smaller tubercles (sometimes called contact organs) can also appear elsewhere on a fish’s body. The small tubercles appearing on the bodies of central stonerollers (Campostoma anomalum) may be used as touch receptors to help locate a mate and keep them close.

When the spawning season comes to an end, the bumps settle down, shrinking in size or falling off – and don’t worry 16 year-old self, your bumps will too.

Upwelling

churning over – boom!
as raw waters were summoned
the terns flew still


Sometimes I find myself in thought avalanches – I ask a question which leads to a second question, which leads to a new question, which leads to another question…

For example, what affects egg quality in fish? Answer: mother. But what affects mother? Answer: her environment. But what aspect of the environment? Answer: food availability. But what affects food availability? Answer: upwelling – one of nature’s remarkably influential processes.

Upwelling – when winds (you know, those blustery kinds where gulls look like they’re frozen in air) gust along a coastline pushing warm surface water offshore causing cold, nutrient-rich water from the ocean’s depth to move upward.

When the deep water, laced with compounds like nitrate and phosphate, reaches the surface, photosynthesizing phytoplankton ferociously consume those nutrients to grow and multiply. Flourishing swaths of phytoplankton are fed upon by zooplankton. Zooplankton are devoured by filter-feeders (perhaps an adorable krill). Filter-feeders are eaten by fishes (that can also eat zooplankton). Fishes are then preyed upon by all – whales, seals, pelicans, cormorants and humans – the latter harvest millions of tonnes of commercially valuable species that thrive in upwelling zones (e.g. anchovy, sardines).

Marine fisheries are definitely dependent on upwelling: about 20% of all catch occurs in upwelling regions, which only cover ~2% of the ocean’s surface!

Wait, 2%? That’s it? Wouldn’t it be swell if there were ways to mimic upwelling in places where this phenomena does not naturally occur? Answer: there are! Could this strategy realistically improve worldwide fish production? Answer: here comes another thought avalanche.

Diadromy

a life betwixt worlds
the fluid chameleon
dives and emerges


Fish like to move. Up, down, left and right, across short distances and long. Fish typically move for food and fornication.

Diadromous fish move between marine and freshwater environments. Two forms of diadromy are catadromy and anadromy. Eels (Anguilla spp.) are a classic catadromous animal – they move from freshwater to spawn in the ocean. Salmon are a classic example of an anadromous animal – they move from the ocean to spawn in freshwater

For Pacific salmon, adults spend a few years in the open ocean gorging on herring and krill and avoiding orcas. Then something clicks and it’s business time. Fish move by the millions back toward the freshwater rivers and streams they were born in. Upon arrival home, a mate is chosen, eggs and sperm are released and then Romeo and Juliet die.

Many significant changes occur to salmon during this transition from salt to freshwater (e.g., fish stop eating, testes and ovaries balloon in size).

One of the most strikingly obvious changes is that of colour. In the ocean, salmon are sleek, silver bullets with a bespeckled top – an outfit that provides camouflage from aquatic and aerial predators. In freshwater, adult salmon transform into colourful beasts – colour likely plays a role in wooing potential lovers.

Sockeye salmon (O. nerka) dress themselves in festive holiday colours – red trunks and green heads and tails. Coho salmon (O. kisutch) also blush a little red. Chum salmon (O. keta) don purplish-black stripes. Male pink salmon (O. gorbusha) grow giant, grey humps. Chinook salmon (O. tshawytscha) shine in an olive hue.

I, myself, prefer tall, dark and handsome – but I suppose in the salmon world that’s a grizzly bear.

Vitellogenesis

assembled layers
engorged with nutrition
her exquisite pearls


Isn’t it amazing, how an egg the size of a pinhead turns into a 2 m long, 200 lb armored giant that wanders meandering rivers for 100 years or more? Sturgeon eggs are tiny but like all fish eggs they are mighty – after all, they contain all the building blocks and tools to make real life fish!

Eggs are filled with maternal DNA of course and also vitamins, metals (to kick-start chemical reactions), hormones, carotenoids (antioxidant power), calcium (for bone growth) and energy sources (e.g. proteins and fats). After fertilization all of these goodies are used to transform the dewy globe into a young fry.

But how does all that stuff get in the egg?

Most items are likely taken up into the developing egg during vitellogenesis. This egg-srtaordinary (ha!) process involves a special protein called vitellogenin being shuttled from the liver into the developing egg. Vitamins, metals, hormones, carotenoids and calcium are thought to be hitching a ride on vitellogenin as it is engulfed into the egg. Once in the egg, vitellogenin is broken down into smaller fat-protein hybrids that will form the nutritious yolk developing fish “consume” and turn into eyes, a body and fins.

P.S. Why are salmon eggs bright orange and sturgeon eggs black? One hypothesis is mom’s diet – in the ocean salmon eat lots of krill which have lots of red-pigment carotenoids that can get deposited into eggs; sturgeon are bottom-feeders vacuuming up worms and snails which are low in red-pigment carotenoids.

Otolith

a full moon duplicates
over abstract mountain peaks
years of growth revealed


In fishes, nestled along each side of the brain are otoliths or “ear bones”. Though technically calcium carbonate rocks, otoliths in fishes are similar to ear bones in humans – they help a fish hear and balance. Fishes have 3 pairs of otoliths: large sagittae which are relatively easy to locate and tiny lapilli and asteriscii which if located are followed by quiet celebrations under the warm glow and constant hum of fluorescent lights in a windowless lab whilst dissecting your nth fish.

Otoliths come in all shapes and sizes. They are even invisible in sharks…because sharks do not have calcified otoliths. You can however find otoliths that once belonged to a fish in the stomachs of sharks (and penguins, seals, dolphins and shrimp!) because otoliths do not decompose as quickly as true bones. Otolith shape and size can also help ID what species of fish a predator consumed.

Mostly commonly associated with otoliths is a fish’s age. As fish grow, new layers of calcium carbonate are added to the otolith. When an otolith is sliced a series of rings are revealed and each ring represents one year – analogous to rings of a tree trunk but not always as easy to see. 

You can also find out whether a fish has been swimming in lakes and rivers or the ocean based on an otolith’s chemical composition. Let’s consider the metal strontium – high levels are found in the marine environment and levels are lower in freshwater. As a fish gets older strontium is incorporated into new otolith layers. Using fancy tools with long acronyms the levels of strontium can be measured in otolith layers – higher levels mean a fish was growing in saltwater, lower levels mean a fish was growing in freshwater. 

These fishy “ear bones” can also adorn human ears.

[update: new study finds farmed fish have otolith deformities]

Pelvic fin

a hallmark extension
that stretched evolutionary time
up, up, up – away


The pelvic fins are a pair of fins located on the bottom of fishes. Hey! My two legs are located on the bottom of me. Hmmm…

First there were lobe-finned fish with pectoral and pelvic fins – they lived 380-390 million years ago. Then the four-legged tetrapods, our ancestors, appeared about 30 million years later with no pectoral fins and no pelvic fins. So what happened in between?

Tiktaalik roseae happened.

Roaming this planet 375 million years ago was Tiktaalik the “fishapod”, part-fish part-tetrapod.

Tiktaalik‘s fossils were found on Ellesmere Island in Nunavut, Canada. First Tiktaalik’s frontal appendages were uncovered – a combination of pectoral fin and structures with the rotational abilities of a shoulder and elbow. Then Tiktaalik‘s hind appendages were unearthed –  a combination of pelvic fin and supportive pelvic bone. Tiktaalik likely lived in shallow, nearshore waters using its pectoral limbs to prop up and scope out the scene. Tiktaalik’s pelvic limbs were surprising – great for swimming and appeared strong enough to support walking underwater…and perhaps on land!

Fishes today retain paired pelvic fins and did not evolve legs. Pelvic fins likely have a role in steadying swimming fish. 

Time for an exception!

Gobies have a fused pelvic fin that resembles a suction cup. A goby uses its fused pelvic fin to perch and pose on rocky substrate, oh, and sometimes climb over waterfalls! The Nopoli rockclimbing goby (Sicyopterus stimpsoni) alternates between a mouth sucker and the pelvic fin sucker to ascend Hawaii’s waterfalls (a.k.a. “inching”). Less dramatically, this characteristic fin is used, among other traits, to identify invasive round goby (Neogobious melanostomus) in North America.

Thus concludes the fin series.

Fin.

Adipose fin

i’m not from your home
a mystery contour is my crux
my place is not fixed


The adipose fin is located between a fish’s caudal (tail) fin and dorsal (back) fin.

Adipose tissue in you and I is another name for fat. Though some species of fishes do have squishy adipose fins, the majority of adipose fins don’t actually contain fat. The name is thought to be derived from a hypothesis of yesteryear – that adipose fins were simply fat storage. This fin, often described as enigmatic, is definitely a mysterious appendage. Persisting in ~6000 species of fishes since the Mesozoic era (~252 to 66 million years ago), researchers have pondered the origin and function of the adipose fin for some time.

In the 1980’s it was noted that in salmonids males consistently have larger adipose fins than females, but why? One hypothesis considered adipose fins as secondary sexual traits used to impress females, like antlers on male deer. Seems like a reasonable idea based on the following observations: 1) spawning females prefer to hang out near males with larger adipose fins, and 2) when males fight the adipose fins of losing, subordinate males appear to shrink over time!

Now what about swimming performance, after all most fish fins are important for movement. When the adipose fin is removed fish put their caudal fin to work, moving it side to side more vigorously to generate a larger amplitude. But this caudal fin workout may be energetically costly for a fish.

It is common practice in hatcheries to remove the adipose fin of salmonids so that fishers can easily distinguish between wild and hatchery-reared fish. Should there be concern for this established fisheries procedure? One study has found the number of fish that return home is the same regardless of whether they have their adipose fin clipped or not clipped.

The latest revelations of the adipose fin – they have appeared multiple times across fish lineages and contain specialized cells that may be able to sense water flow.

Adipose fins, the little fins that could…apparently do much more than originally thought.

Dorsal fin

argosies set sail
we’ve bounty to capture
and lands to defend!


I saw my first ocean sunfish while visiting Valencia’s Oceanogràfic and giggled. How silly that this fish’s pectoral fins look like ears. Where did this beast’s caudal fin go? Why, the anal fin is symmetrical to the dorsal fin protruding from its back!

For most fishes the dorsal fin helps stabilize the animal so it doesn’t somersault endlessly through water.

The dorsal fin of Mola mola is dual purpose; balance and boost. Without a proper caudal fin these basking beauties must rely on waving their dorsal (and anal) fin to achieve forward momentum while exploring Earth’s oceans.

Sailfish (Istiophorus spp.) dorsal fins are pretty extraordinary too. When hunger strikes sailfish erect their massive dorsal fin (which basically runs the length of their 3 m bodies) and launch at schools of small fish. Imagine how confused you would be if dozens of shower curtains charged at you from all angles. The frazzled prey fish crowd into a swirling mass called a baitball. Sailfish take turns striking at the baitball to satisfy their appetites.

How about that billowing cape on Arctic grayling (Thymallus arcticus)? Their characteristically bespeckled and multicoloured dorsal fin is rather exquisite. Both males and females raise their dorsal fin tall to threaten other grayling that may be creeping too close to home (i.e. 1 mof gravel in an Arctic stream). Males are also observed draping their dorsal fins over the backs of females during spawning; possibly keeping a female close from other suitors or perhaps an affectionate side-hug.

Egg-spots

his necessary trick
for romance or rivalry?
the artists’ signature


Whenever I go to the grocery store I am amazed at the numerous assortment of eggs; free-range, AA, pasteurized, organic, brown, white, omega-3 enriched and vitamin-enhanced. I feel a similar (actually, a remarkably amplified) wonderment when I am reminded that there are 2000-3000 kinds of cichlid fishes!

What do you get when you combine eggs and cichlid fishes? Egg-spots!

One of among hundreds of curiosities of this fascinatingly diverse group of fishes is egg-spots or egg-dummies. Unique to haplochromines, egg-spots resemble fish eggs in size, shape (circular) and colour (yellow-orange-reddish), and are located on the male cichlid’s anal fin, a relatively unexplained fin in comparison to others (e.g. caudal, pectoral).

It’s important to know that haplochromines are mouth-brooders; a female lays her eggs and picks them up in her mouth, then the eggs are fertilized and she rears the progeny in her mouth. How are the eggs fertilized you ask? The thought is that females nip at a male’s egg-spots thinking they haven’t picked up all their eggs and while doing so the male releases his sperm (via an opening anterior to the anal fin) which fertilizes the eggs in her mouth.

Aren’t fish great?

Interestingly, the size, shape, colour and number of egg-spots varies among males, species, and whether the water is clear or muddy. Some females prefer males with lots of larger spots, but brightly coloured polka dots may make males stick out like a sore thumb, err, fin to predators. Most recently discovered is that males with fewer egg-spots get beat up more often by other males.

Clearly the story of these curious spots is not yet FINished.

P.S. In other fishes the anal fin is involved with balance while swimming and the spines in the anal fin can be used to age a fish.