Arxiu d'etiquetes: elasmobranchii

CONTENTS, ENGLISH, FISHES, ZOOLOGY

How do fish breathe?

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It’s probable that you know that most of the fishes that inhabit in the Earth breathe due to the presence of gills. However, this is not the only respiratory system present in fishes. In this post, we will review different types of breathing in fishes. 

INTRODUCTION

The respiratory system of fishes have to be adapted to two important limitations of underwater life. On the one hand, the amount of dissolved oxygen is smaller in the water than in the air: at 23ºC, air has 210 ml of oxygen per litre of air, while in freshwater is about 6,6 ml/l and in salt water is 5,3 ml/l. On the other hand, water is much more dense and viscous than air. These limitations explain the adaptations in the breathing of this group of animals.

BREATHING WITH GILLS

The oral cavity of teleostei fishes (modern ray-finned fishes) is communicated with the exterior through the mouth and pharyngeal pouches, lateral openings present in the pharynx in which the gills develop. Thanks to the opercle (or gill cover), a hard structure placed in each side of the head, gills are protected.

The structure of the gills is complex. From branchial arches, curved structures that pierce through pharyngeal pouches in each side of the head, two gill filaments grow forming a V. These filaments produce the gill lamellas, folds of the wall’s filaments with a perpendicular disposition. In each side of the filament, we may find between 10 to 40 lamellas per mm. So, it is in these lamellas where the gas exchange happens because they are a very thin wall of tissue and are well supplied with blood.

Structure of the fishes' gills (Picture: AS Biology Ms Timms).
Structure of the fishes’ gills (Picture: AS Biology Ms Timms).

So, the oxygenated water that passes through the mouth cross the gills and finally abandon the oral cavity through the opercle, while the blood flows in the opposite direction across lamellas to catch the oxygen.

The larva of many fishes have external gills in each side of the head. In the rest of phases, gills become internal. Fishes with a respiration with gills are hagfishes, lampreys, elasmobranchii and bony fishes.

Les mixines són peixos amb respiració branquial (Foto: Natureduca).
The hagfish is a species with a breathing with gills (Picture: Natureduca).

BREATHING WITH LUNGS

About 400 bony fish species are known to have the ability of breathing from air, most of them living in freshwater ecosystems. Anyway, most of them have both gills and lungs. These species with the two mechanisms usually use the air in certain occasions:

  • When the oxygen level in the water goes down.
  • When the temperature increases, so the higher the temperature is, the higher are the oxygen necessities.

Lungfishes (Dipnoi) are among the species with the most advanced system. Their lungs have crests and septums similar to those in the lungs of amphibians. The Australian lungfish (Neoceratodus) can breathe with both gills and a lung. African lungfishes (Protopterus) and the South American lungfish (Lepidosiren) breathe with a complex lung and single gills. These fishes need to compulsorily breathe air, as in the contrary they die.

Peixos pulmonats: Peix pulmonat australià (Neoceratodus forsteri), africà (Protepterus annectens) i sud-americà (Lepidosiren paradoxa) (Foto: Encyclopaedia Britannica).
Lungfishes: Australian lungfish (Neoceratodus forsteri), African lungfish (Protepterus annectens), South American lungfish (Lepidosiren paradoxa) and Devonian lungfish (Dipterus) (Picture: Encyclopaedia Britannica).

OTHER BREATHING MECHANISMS IN FISHES

Many fishes have the capacity of breathing through the skin, specially when they are born because they are so small that they do not have specialised organs. As the animal is growing, gills or/and lungs are developing because the diffusion through the skin is not enough. Anyway, skin may be responsible of a 20% or more of gas exchange in some adult individuals. Others can do it through the mouth, the pharynx, the oesophagus, the intestine or the rectum, as is the case of Hoplosternum.

El peix Hoplosternum té la capacitat de respirar a través del tub digestiu (Foto: Free Pet Wallpapers).
Hoplosternum has the ability of breathing through the digestive tube (Picture: Free Pet Wallpapers).

Some species have developed cavities beyond the gills, the suprabranchial chambers, which can be filled of air. In other, complex organs developed from a very irrigated branchial arch can be formed and act as a lung. This is the case of the catfish and Electrophorus .

Some fishes have the ability to breathe air without a specific adaptation. This is the case of the American eel (Anguilla rostrata), that cover the 60% of the oxygen requests through the skin and the 40% swallowing air from the atmosphere.

REFERENCES

  • Notes of the subject Chordates of the Degree in Biology (University of Barcelona).
  • Hickman, Roberts, Larson, l’Anson & Eisenhour (2006). Principios integrales de Zoología. Ed. McGraw Hill (13 ed)
  • Hill, Wyse & Anderson (2006). Fisiología animal. Ed. Medica Panamericana

Difusió-anglès

CONTENTS, ENGLISH, ENVIRONMENT, FISHES, Impact of fishing, MARINE ENVIRONMENT, ZOOLOGY

Sharks: predators as prey

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Today we will talk about a sensitive topic. This topic is shark finning, an unsustainable and macabre practise that happen in our waters. 

INTRODUCTION

Sharks, together with rays, are included in the elasmobranchii group. They are characterized by a cartilaginous skeleton and several teeth rows, which are continuously renovated. Sharks are predators because they are in the top of food chains. It means that they devour but they aren’t devoured. Nevertheless, we will see that is not completely true, as there is a species that has the ability to capture them, cut their fins and then to throw them to the sea.

WHAT IS SHARK FINNING?

Shark finning consists on cutting and saving shark fins and discard the rest of the body.

4145Fisher cutting a shark fin (Foto: Gary Stokes; Sea Shepherd, Hong Kong).

The animal usually is still alive when is thrown into the water, so it can swim and sink slowly to the deep sea; where, still alive, will be food for other animals. Fishers only save the fins because its economical value is much bigger than the meat of the animal so, discarding the body, they have more space in the ship for fins. In the next video, which is very hard to see, we can watch this activity:

IS THAT ILLEGAL?

Shark finning is a forbidden activity around Europe since 2003, with the passing of the Council Regulation (EC) No 1185/2003 of 26 June 2003 on the removal of fins of sharks on board vessels, but this law allowed to discharge fins without its body, with a permission, and in the case that the fin weight was lower than 5% of the total weight of the animal. This means that, despite the law, finning was taking place. This regulation had some legal vacuums, thanks to 4th article, that allowed to give special permissions to cut fins on board of the vessels and discharge these fins and the rest of the body in different harbours, what meant a big difficulty to control finning.

For all this reasons, in 2011, European Commission proposed the obligatory nature to discharge fins together with the shark body, what was well received by conservationist organisations, most of the scientific community, general public, Committee of Ministers of EU and the Environment Committee of EU. Nevertheless, Spain and Portugal, whose shark fisheries are by far the most important in EU, express their opposition to this reform. Both countries have a fishing line fleet in the North Atlantic.

Finally, in June 2013, it is approved the reform of the European reform about finning, Regulation (EU) Nº 605/2013 of the European Parliement and of the Council (of 12 June 2013), amending Council Regulation (EC) No 1185/2003 on the removal of fins of sharks on board vessels. In this regulation, it is mandatory to discharge sharks with their fins. This measure has been successfully to fight against finning in other parts of the world. Portugal and Spain were put up it because it reduces their benefits, so holds are full sooner.

WHY IS THAT HAPPENING?

This practise was expanded due to the high price of shark fins in the Asiatic market to do shark fin soup and in traditional cures. Every single kilo of fresh or frozen fin costs 20 €, while in the case of meat the value is just 1€. EU captures sharks in the Mediterranean and the Atlantic, Indian and Pacific oceans. It is the first worldwide power in shark fishing, with a 17% of declared captures in 2009, and the biggest fin exporter at Hong Kong and China.

_MG_7002Shark fins spread in the ground to be dried (Gary Stokes; Sea Shepherd, Hong Kong).
_MG_7411Shark fins spread in the ground to be dried (Gary Stokes; Sea Shepherd, Hong Kong).

WHICH SPECIES ARE THE TARGET?

Nowadays, many species are target of fishing because, despite 28% of the species are considered threatened by IUCN, just some of them are protected. In Spain and Europe, there are just 9 protected species. In addition, catch shares don’t exist and, for this reason, fishers can fish till extinction. Why do not exist catch shares? The reason is that fishing regulation in EU is conditioned by Spain and Portugal. However, specialists estimates that every year are killed 100 million sharks for their fins.

Blue shark is the main species in the Atlantic fishing line feet. If we have a look in the capture statistics of this shark in Vigo harbour (Spain) (2468 tones and more than 3 million euro of benefit, according to Puerto de Vigo), we can observer that is a great benefit: is legal, there aren’t catch shares and fins are well-paid in Hong Kong market.

WHICH IS THE IMPACT OF SHARK FINNING?

Shark finning has the following impacts:

  • Loss and devastation of shark populations around the world. Experts estimate that within a decade, most species of sharks will be lost because of longlining.
  • Unsustainable fishery. The massive quantity of sharks harvested and lack of selection deplete shark populations faster than their reproductive abilities can replenish populations.
  • Threatens the stability of marine ecosystems.
  • Obstructs the collection of species-specific data that are essential for monitoring catches and implementing sustainable fisheries management.
  • Wasteful of protein and other shark-based products. Up to 95 per cent of the shark is thrown away.

REFERENCES

ACKNOWLEDGEMENT

I wouldn’t finish this article without give thanks for her help and patient to Mónica Alonso Ruiz, who is communication responsible and Madrid responsible of Alianza Tiburones Canarias, who informed me and give me most of the information and data present here.

If you find this article interesting, you can share it in Social Networks to dissiminate this problem. The goal of this blog is to inform people about science. 

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