Erzsebet Frey

Bluefin tuna are not egg-laying fish, they are live-bearing fish which means that they give birth to live young. When bluefin tuna reproduce, the female releases eggs which are then fertilized internally by the male, and the young develop within the female until they are born. Bluefin tuna typically produce a large number of eggs, with a single female able to produce millions of eggs in a single spawning season.

How many eggs do bluefin tuna lay?

Scientific name: Thunnus thynnus  
Scientific classification:  
Phylum: Chordata  
Class: Actinopterygii  
Order: Perciformes  
Family: Scombridae

## Description of Northern Bluefin Tuna {#description-of-northern-bluefin-tuna .wp-block-heading}

The pectoral fins are long and rigid and are positioned just behind the
conical head, with a large mouth and eyes. The back of the
[fish](https://simplyecologist.com/fish-with-horns/) is a deep
bluish-purple and the underside is shimmering silver. The largest
bluefin tuna ever recorded weighed over 750 kg and was around 3 m long.

Where does she live? This fish is found in the Atlantic Ocean and ranges
throughout this expansive body of water, including temperate and
tropical waters from the far north to the Mediterranean, the Black Sea,
and the coasts of Brazil and West Africa.

## Hydrodynamic perfection {#hydrodynamic-perfection .wp-block-heading}

Bluefin tuna is probably the pinnacle of fish
[evolution](https://simplyecologist.com/history-of-the-wolves/) in terms
of swimming ability. Its body is so well adapted to its way of life that
it can cruise for thousands of miles with ease and in the pursuit of
prey or escaping from danger it can accelerate to speeds more than a
match for all but the
[fastest](https://simplyecologist.com/what-animal-is-the-fastest-killer/)
boats.

Such [speed](https://simplyecologist.com/how-long-can-cheetah-run/) and
power are made possible by the huge muscle mass of this fish. The whole
animal is little more than a dense block of muscle. From the skeleton
outwards there is layer after layer of muscle fibers which pull together
to guide the sickle-shaped tail through the water in short, powerful
sweeps.

Much of the tuna muscle has a limited ability to use the oxygen present
in animal blood; it is anaerobic, so most of the energy is generated in
the absence of oxygen. This activity in the absence of oxygen leads to
the buildup of lactic acid, resulting in muscle fatigue.

A much smaller proportion of fish muscle mass is dependent on oxygen
carried in the blood and is this aerobic tissue, tapering down the sides
of the body to the tail, which contracts to provide the slow, steady
action required for long-distance cruising.

Both of these muscle groups channel their straining effort through a
pair of tendons anchored to the sickle-shaped tail fin. With each flick
of the tail, in contrast to most other fish, the whole of the body
remains more or less rigid, increasing the efficiency of each stroke.

In
[fast](https://simplyecologist.com/what-animal-is-the-fastest-killer/)
and furious swims, the progress of the tuna through the water is even
more enhanced by the other fins nestling in shallow depressions on its
body, reducing drag. An interesting arrangement of blood vessels allows
it to [swim](https://simplyecologist.com/can-red-wolves-swim/) in waters
cold enough to discourage other fish.

The effort of the animal's muscles generates a large amount of heat and
this heat is captured by a heat exchange system where it is passed to
cold blood traveling to the central nervous system and eyes, keeping
them responsive even in chilly, temperate waters. This is a huge plus
for bluefin tuna because it allows the animal to hunt effectively in
waters, normally the reserve of warm-blooded creatures, such as marine
mammals.

## Facts about Northern Bluefin Tuna {#facts-about-northern-bluefin-tuna .wp-block-heading}

• In addition to northern bluefin tuna, the world's oceans are also home
to southern bluefin tuna and Pacific bluefin tuna. There are nine other
species of tuna, all of which have a similar appearance to bluefin tuna
but are noticeably smaller. All the tuna and their relatives, the
mackerels and bonitos are carnivores adept at using their great bursts
of speed to capture prey.

• The heat exchange system of the bluefin tuna enables it to hunt as far
north as the cold waters off Newfoundland.

• Bluefin tuna competes with a few other species for the fastest crown
of fish. There is the sailfish and the marlin, both of which are reputed
to reach speeds of 100+ kmhi short bursts.

• Tuna gills are ventilated by the fast-flowing water that surrounds
them as the animals swim. Tagged individuals have been tracked from the
East Atlantic to the West Atlantic and back again in one year and it is
very likely they cover even greater distances. During their ceaseless
oceanic wanderings, they tend to stay quite near the surface but they
dive to depths of almost 1,000 m to hunt.

• The tuna has small deposits of magnetite in its head and these are
thought to act as a built-in compass, allowing fish to orient themselves
in the vastness of the open ocean.

• Bluefin tuna grows quite slowly. can live at least 30 years.

• The large size of the tuna and the quality of the flesh has made it a
favorite of fishermen everywhere. The bluefin tuna, with its enormous
size, is the most coveted of these fish and unfortunately today it is
the rarest species.

Before 1970, the bluefin tuna was not held in high esteem. Captured
specimens were normally returned for use in pet food. Then, the species
rapidly gained a following in Japan as something of a delicacy. A large
fishery grew and today stocks are severely depleted to the extent where
fine examples now command huge prices.

A 200 kg specimen sold in 2001 fetched over \$173,000. They span
thousands of square miles of open ocean, and in many cases, longline
fishing is the weapon of choice. Longlining consists of paying up to 130
km of line bristling with thousands of hooks and has many negative
effects.


Scientific name: Thunnus thynnus Scientific classification: Phylum: Chordata Class: Actinopterygii Order: Perciformes Family: ScombridaeDescription of Northern Bluefin Tuna  The pectoral fins are long and rigid and are positioned just behind the conical head, with a large mouth and eyes. The back of the fish is a deep bluish-purple and the underside is shimmering silver.

Northern Bluefin Tuna Facts

Scientific name: Electrophorus electricus  
Scientific classification:  
Phylum: Chordata  
Class: Actinopterygii  
Order: Gymnotiformes  
Family: Gymnotidae

The adult electric eel is an elongated, snake-like animal that reaches
2.5 m in length and 20 kg in weight. Due to their serpentine shape, they
lack caudal, pectoral, and dorsal fins; the anal fin is well-formed and
extends almost the entire length of the body. The entire body is
cylindrical, with a flattened head and a large mouth. This fish's skin
varies from gray to brown/black with a white/yellow patch under the chin
and throat. The electric eel is not quite an eel; In fact, it is a type
of knifefish.

The electric eel is native to the rivers and lakes of northern South
America. They are terrestrial creatures that hide in the mud and rocks
of rivers and swamps, usually in very shady areas. At first glance,
there seems to be very little special about this
[fish](https://simplyecologist.com/fish-with-horns/), and yet, as the
name suggests, the electric eel has some amazing adaptations.

The eel's vital organs are all located in the front part of the animal
and take up only about 20 percent of the fish's internal volume,
considerably less than other fish. It has three distinct groups of
modified muscles that have long ceased to contract for movement.

The electric eel' breathes air, getting about 80% of its oxygen from the
air. Air-breathing allows fish to live in waters where there is very
little dissolved oxygen.

The cells of the main electrical organ of the fish form 5,000 to 6,000
disks stacked like plates. The small electrical impulses generated by
each of these plates are harnessed and channeled to create a stream of
electrical energy that the fish uses in various ways. The electricity
generated by the fish is very weak and is generated as a pulsed signal
by the organ of Sachs.

Aside from navigation and foraging, the electric field can be maximized
by other triggers, when the eel is in danger or anticipates the approach
of a nutritious snack. In a burst of short, sharp discharges, the eel
can generate 650 volts with a current of 1 ampere. This pulsed wave of
electricity penetrates the water and is powerful enough to
[kill](https://simplyecologist.com/which-animal-kills-humans-the-most/)
a human or even a horse from a distance of 6m.

Fish need a lot of energy to generate these high voltages, but they can
do so intermittently for at least an hour to maintain the strength of
each shock.

The ability to generate, store and use electricity is not unique to the
electric eel. Many other fish shares this ability. The only species
capable of generating tension even partially comparable to the electric
eel are the African electric catfish and torpedo rays, of which there
are 69 species.

There are many electric fish such as star watchers,
[elephant](https://simplyecologist.com/which-animal-kills-humans-the-most/)
noses, many species of knife fish, and rays. In all but the electric
eel, electric catfish, and torpedo ray, electricity is used to find food
or navigate. Electricity generation is relatively rare in marine fish,
but more common in freshwater species that live in murky waters.

The only known mammal with an electrical sense is the platypus. Like
many other electric fish, the electric eel is nocturnal. It will hunt
anything small enough at night to be sucked into its wide jaws.

The electric eel is also unusual for its reproductive
[behavior](https://simplyecologist.com/what-is-the-behavior-of-red-pandas-in-the-wild/).
In the dry season, a male eel uses its saliva to build a nest in which
the female lays her
[eggs](https://simplyecologist.com/how-many-eggs-do-bluefin-tuna-lay/).
Up to 17,000 young hatches from the eggs in one nest.

The powers of electric fish are hard to overlook and have been known
since ancient times. The ancient Romans stood in a shallow bath with a
torpedo and killed themselves to relieve gout symptoms.

Electric eels have always been high on the list of brave (or foolish)
zoo collectors. Some unfortunate horses or mules were herded into a pool
of water inhabited by several fish, where they took enough beatings to
at least knock them out. The fish's batteries would eventually
[run](https://simplyecologist.com/how-long-can-cheetah-run/) out,
allowing collectors to come up with strong nets and boots.


Scientific name: Electrophorus electricus Scientific classification: Phylum: Chordata Class: Actinopterygii Order: Gymnotiformes Family: Gymnotidae The adult electric eel is an elongated, snake-like animal that reaches 2.5 m in length and 20 kg in weight. Due to their serpentine shape, they lack caudal, pectoral, and dorsal fins; the anal fin is well-formed and extends almost the entire length of the body.

How does electric eel work?

Scott Edmunds

**Deep (ocean) sequencing. Big-(fish) data.  
![mola_mola](http://gigasciencejournal.com/blog/wp-content/uploads/2016/09/Mola_mola-300x265.jpg){.alignright
.size-medium .wp-image-1838 loading="lazy" decoding="async" width="300"
height="265"
srcset="http://gigasciencejournal.com/blog/wp-content/uploads/2016/09/Mola_mola-300x265.jpg 300w, http://gigasciencejournal.com/blog/wp-content/uploads/2016/09/Mola_mola-768x677.jpg 768w, http://gigasciencejournal.com/blog/wp-content/uploads/2016/09/Mola_mola-1024x903.jpg 1024w, http://gigasciencejournal.com/blog/wp-content/uploads/2016/09/Mola_mola.jpg 1345w"
sizes="(max-width: 300px) 100vw, 300px"}**The ocean sunfish, must
officially be one of the [world's
weirdest](https://www.youtube.com/watch?v=U60obmWODLQ&feature=youtu.be)
creatures to enter the ["genome
club"](https://twitter.com/sketchscience/status/748231202939748352), and
have its genetic code mapped. Laying the most eggs of any other known
vertebrate (up to 300,000,000 at a time), and starting out as the size
of the head of a pin, sunfish grow to become to largest bony fish in the
sea. Eventually weighing up to 2,300kg and measuring up to 3.3m in
length, the ocean sunfish has been observed to grow at almost one
kilogram per day. To put this in context, other fish grow at 0.02 to 0.5
kilogram per day. The morphology of the ocean sunfish is also very
different from other fish, having lost its caudal fin and hence also
known as a "half-fish". Despite "[Survive! Mola
mola](https://play.google.com/store/apps/details?id=jp.selectbutton.manbotheworld&hl=en)!"
being one of the most popular video games in Japan, how they manage to
survive and grow so rapidly from munching nutritionally poor jellyfish
is an interesting challenge to understand from a scientific perspective
as well.

Wading into this challenge have been a team of scientists including the
[lab of Byrappa Venkatesh and Sydney
Brenner](http://www.imcb.a-star.edu.sg/php/venkatesh.php), who, [in
2002](http://science.sciencemag.org/content/297/5585/1301.long) brought
the genome sequence of the Pufferfish (*Takifugu rubripes*) to light,
making it the second vertebrate genome to be sequenced. *Fugu* was found
(at the time) to have [the smallest genome](http://www.fugu-sg.org/) of
any vertebrate, at 390Mb roughly one eight the size of the human genome,
making it an excellent 'reference' genome for understanding the
structure and evolution of genomes. As one of the closest relatives of
the *Takifugu rubripes*, the group were interested to see how compact
the *Mola mola* genome was, but being 730 Mb this is compact for a
vertebrate genome, but not spectacularly so.

Venkatesh, who led the project from A\*STAR, said: "Pufferfish and ocean
sunfish belong to the same order but differ dramatically in morphology.
At the early stages of development, ocean sunfish larvae look similar to
pufferfish larvae with spines sticking out. We thought ocean sunfish
would be a useful species to identify the genetic basis of morphological
innovations. So we were keen to sequence the ocean sunfish genome and
compare with the pufferfish genome, to identify genetic changes that
have occurred in the sunfish lineage and that might give clues to the
highly derived phenotype."

**The Genome in Sydney Brenner's hand luggage.  
**

::: {#attachment_1835 .wp-caption .alignleft style="width: 310px"}
![Brenner visiting BGI in
2010.](http://gigasciencejournal.com/blog/wp-content/uploads/2016/09/brenner-300x232.jpg){.size-medium
.wp-image-1835 loading="lazy" decoding="async"
aria-describedby="caption-attachment-1835" width="300" height="232"
srcset="http://gigasciencejournal.com/blog/wp-content/uploads/2016/09/brenner-300x232.jpg 300w, http://gigasciencejournal.com/blog/wp-content/uploads/2016/09/brenner-768x594.jpg 768w, http://gigasciencejournal.com/blog/wp-content/uploads/2016/09/brenner-1024x792.jpg 1024w, http://gigasciencejournal.com/blog/wp-content/uploads/2016/09/brenner.jpg 1961w"
sizes="(max-width: 300px) 100vw, 300px"}

Brenner visiting BGI in 2010.
:::

Nearly two decades on from the initiation of the project, Sydney
Brenner, has given some further background on how it came about: "I
became interested in the *Mola mola* in the 1990's, not long after we
began work on the Pufferfish, Fugu. We chose that genome because it was
the smallest one reported and reading about the evolution of fishes made
me interested in the *Mola mola*. It seemed to be the end of the line
with many features lost. I tried for many years to obtain a sample but
failed. There was one on display at the aquarium in Northern California
but when it died it was their policy to return it to the ocean. When I
visited the Marine sciences laboratory in Florida I mentioned my
interest in it. To my great surprise, Paul Linser who had worked with in
the Scripps telephoned me one day to tell me that a *Mola mola* had swum
up the intercoastal canal and had been found by the private aquarium
close to the Marine Laboratory. It would be exhibited there and when it
died he would arrange for me get some blood. This was our sample which
was brought to me frozen in liquid nitrogen to the Scripps and which I
carried to Singapore and which we used for the sequencing. Fish have
nucleated red blood cells a very useful source of DNA. We still have
many friends in marine institutes to help us in this exotic interest."

Despite the less interesting genome size meant the species was passed
over for much of the genome evolution work, being a bizarre "natural
mutant" meant there was continuing interest in studying the
extraordinary phenotypes. With the launch of the G10K project to
sequenced 10,000 vertebrate species, this was high on the list for BGI
to sequenced as part of their pilot to 100 species for the consortium.
Funded by [China National Genebank
(CNGB)](http://www.cngb.org/en/index.html), Guojie Zhang, Associate
Director of CNGB, and a corresponding author says: "This is one of the
30 fish genomes have been sequenced for the G10K project. The
availability of high throughput DNA sequencing technology makes it
possible to sequence whole genomes of a wide range of 'non-model'
species, allowing us to uncover the genetic basis of their phenotypic
diversity and their adaptation. Our study mainly focused on the genetic
background of the ocean sunfish's fast growth rate and particular body
shape. We found that several genes involved in growth hormone signalling
evolve very fast in the ocean sunfish when compared to other bony
fishes, which may explain its large size and fast growth rate."

Venkatesh added: "We found changes in genes encoding for collagen and
cartilage formation. This may contribute to the development of
predominantly cartilaginous skeleton in this gigantic fish. Vertebrates
exhibit a wide diversity in their morphology, physiology and behaviour.
Understanding the genetic basis of this diversity is a major goal of
evolutionary biology." Further adding "I think we still have a lot to
learn from the sunfish genome assembly. One way to pinpoint more genetic
changes specific to sunfish would be to sequence more closely related
species such as porcupine fish, box fish, triggerfish, and triplespines
(all are tetraodontiformes fishes) and a closest outgroup to this Order.
Our present analysis also suggests that the genetic changes underlying
many of the derived phenotypes could be in the regulatory sequences."

The genomics data is available in the public databases [and
GigaDB](http://dx.doi.org/10.5524/100214) for others to mine and do
these future comparative studies. With us recently publishing a project
announcement for the ["Transcriptomes of 1,000 Fishes"
(Fish-T1K)](http://gigascience.biomedcentral.com/articles/10.1186/s13742-016-0124-7)
project (also featuring Venkatesh) and the genome of the [channel
catfish](http://gigascience.biomedcentral.com/articles/10.1186/s13742-016-0142-5),
fish 'omics research is reaching a high water mark, but few of these
coming genome projects will likely be as bizarre as this new
[paper](http://gigascience.biomedcentral.com/articles/10.1186/s13742-016-0144-3)
looking at these gentle giants of the deep.

### References

Pan H, Yu H, Ravi V, Li C, Lee AP, Lian MM, Tay BH, Brenner S, Wang J,
Yang H, Zhang G, Venkatesh B. The genome of the largest bony fish, ocean
sunfish (Mola mola), provides insights into its fast growth rate.
Gigascience. 2016 Sep 9;5(1):36.
https://doi.org/10.1186/s13742-016-0144-3

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**Deep (ocean) sequencing. Big-(fish) data. **The ocean sunfish, must officially be one of the world’s weirdest creatures to enter the “genome club”, and have its genetic code mapped. Laying the most eggs of any other known vertebrate (up to 300,000,000 at a time), and starting out as the size of the head of a pin, sunfish grow to become to largest bony fish in the sea.

Postagens de Rogue Scholar

How many eggs do bluefin tuna lay?

Northern Bluefin Tuna Facts

How does electric eel work?

Of big fish and small genomes. Ocean sunfish shines.