Bulbus arteriosus

In the circulatory system of fish, the bulbus arteriosus is a pear shaped chamber that functions as a capacitor, maintaining continuous blood flow into the gill arches.

References

1. "ZFIN: Anatomical Structure: Bulbus Arteriosus." ZFIN: The Zebrafish Model Organism Database. Web. 8 May 2011. <http://zfin.org/action/anatomy/term-detail?anatomyItem.zdbID=ZDB-ANAT-011113-107>.

Cardiodectes medusaeus

Cardiodectes medusaeus is a species of copepods in the family Pennellidae. It is a parasite of fish.

In the cnidarian Hydrichthys sarcotretis, parasitism is taken a stage further when the hydrozoan attaches itself to the C. medusaeus. This is itself an ectoparasite of the Northern lampfish (Stenobrachius leucopsarus) in the family Myctophidae. The copepod attaches itself to the bulbus arteriosus of the fish. Such a parasitic chain is known as hyperparasitism. C. medusaeus requires two hosts for proper development. It will go through five successive postembryonic stages, then only the postmated females will go into the pericardial cavity of a lanternfish. The actions of the copepod castrate its fish host. Both male and female fish do not reproduce and seem to grow faster when attacked by the copepod and it seems to have a negligible energy demand from them. The hydrozoan parasite castrates the copepod, a process called hypercastration.

Fish

Fish are gill-bearing aquatic craniate animals that lack limbs with digits. They form a sister group to the tunicates, together forming the olfactores. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Tetrapods emerged within lobe-finned fishes, so cladistically they are fish as well. However, traditionally fish are rendered paraphyletic by excluding the tetrapods (i.e., the amphibians, reptiles, birds and mammals which all descended from within the same ancestry). Because in this manner the term "fish" is defined negatively as a paraphyletic group, it is not considered a formal taxonomic grouping in systematic biology, unless it is used in the cladistic sense, including tetrapods. The traditional term pisces (also ichthyes) is considered a typological, but not a phylogenetic classification.

The earliest organisms that can be classified as fish were soft-bodied chordates that first appeared during the Cambrian period. Although they lacked a true spine, they possessed notochords which allowed them to be more agile than their invertebrate counterparts. Fish would continue to evolve through the Paleozoic era, diversifying into a wide variety of forms. Many fish of the Paleozoic developed external armor that protected them from predators. The first fish with jaws appeared in the Silurian period, after which many (such as sharks) became formidable marine predators rather than just the prey of arthropods.

Most fish are ectothermic ("cold-blooded"), allowing their body temperatures to vary as ambient temperatures change, though some of the large active swimmers like white shark and tuna can hold a higher core temperature.Fish can communicate in their underwater environments through the use of acoustic communication. Acoustic communication in fish involves the transmission of acoustic signals from one individual of a species to another. The production of sounds as a means of communication among fish is most often used in the context of feeding, aggression or courtship behaviour. The sounds emitted by fish can vary depending on the species and stimulus involved. They can produce either stridulatory sounds by moving components of the skeletal system, or can produce non-stridulatory sounds by manipulating specialized organs such as the swimbladder.Fish are abundant in most bodies of water. They can be found in nearly all aquatic environments, from high mountain streams (e.g., char and gudgeon) to the abyssal and even hadal depths of the deepest oceans (e.g., gulpers and anglerfish), although no species has yet been documented in the deepest 25% of the ocean. With 33,600 described species, fish exhibit greater species diversity than any other group of vertebrates.Fish are an important resource for humans worldwide, especially as food. Commercial and subsistence fishers hunt fish in wild fisheries (see fishing) or farm them in ponds or in cages in the ocean (see aquaculture). They are also caught by recreational fishers, kept as pets, raised by fishkeepers, and exhibited in public aquaria. Fish have had a role in culture through the ages, serving as deities, religious symbols, and as the subjects of art, books and movies.

Fish anatomy

Fish anatomy is the study of the form or morphology of fishes. It can be contrasted with fish physiology, which is the study of how the component parts of fish function together in the living fish. In practice, fish anatomy and fish physiology complement each other, the former dealing with the structure of a fish, its organs or component parts and how they are put together, such as might be observed on the dissecting table or under the microscope, and the latter dealing with how those components function together in living fish.

The anatomy of fish is often shaped by the physical characteristics of water, the medium in which fish live. Water is much denser than air, holds a relatively small amount of dissolved oxygen, and absorbs more light than air does. The body of a fish is divided into a head, trunk and tail, although the divisions between the three are not always externally visible. The skeleton, which forms the support structure inside the fish, is either made of cartilage, in cartilaginous fish, or bone in bony fish. The main skeletal element is the vertebral column, composed of articulating vertebrae which are lightweight yet strong. The ribs attach to the spine and there are no limbs or limb girdles. The main external features of the fish, the fins, are composed of either bony or soft spines called rays which, with the exception of the caudal fins, have no direct connection with the spine. They are supported by the muscles which compose the main part of the trunk. The heart has two chambers and pumps the blood through the respiratory surfaces of the gills and on round the body in a single circulatory loop. The eyes are adapted for seeing underwater and have only local vision. There is an inner ear but no external or middle ear. Low frequency vibrations are detected by the lateral line system of sense organs that run along the length of the sides of fish, and these respond to nearby movements and to changes in water pressure.Sharks and rays are basal fish with numerous primitive anatomical features similar to those of ancient fish, including skeletons composed of cartilage. Their bodies tend to be dorso-ventrally flattened, they usually have five pairs of gill slits and a large mouth set on the underside of the head. The dermis is covered with separate dermal placoid scales. They have a cloaca into which the urinary and genital passages open, but not a swim bladder. Cartilaginous fish produce a small number of large, yolky eggs. Some species are ovoviviparous and the young develop internally but others are oviparous and the larvae develop externally in egg cases.The bony fish lineage shows more derived anatomical traits, often with major evolutionary changes from the features of ancient fish. They have a bony skeleton, are generally laterally flattened, have five pairs of gills protected by an operculum, and a mouth at or near the tip of the snout. The dermis is covered with overlapping scales. Bony fish have a swim bladder which helps them maintain a constant depth in the water column, but not a cloaca. They mostly spawn a large number of small eggs with little yolk which they broadcast into the water column.

Fish physiology

Fish physiology is the scientific study of how the component parts of fish function together in the living fish. It can be contrasted with fish anatomy, which is the study of the form or morphology of fishes. In practice, fish anatomy and physiology complement each other, the former dealing with the structure of a fish, its organs or component parts and how they are put together, such as might be observed on the dissecting table or under the microscope, and the later dealing with how those components function together in the living fish.

Hydrichthys

Hydrichthys is a genus of colonial marine hydrozoans formerly placed in the family Hydrichthyidae but is now included in the family Pandeidae. The polyps of members of this genus are parasitic. The polyp attaches itself to a fish, and in one species exhibits hyperparasitism by attaching itself to a copepod, itself the parasite of a fish.

Hydrichthys sarcotretis

Hydrichthys sarcotretis is a species of colonial marine hydrozoans now included in the family Pandeidae. The polyps of members of this genus are parasitic and attach themselves to a fish. H. sarcotretis is a species that exhibits hyperparasitism by attaching itself to a copepod, itself the parasite of a fish.

In H. sarcotretis, parasitism is taken a stage further when the hydrozoan attaches itself to the copepod Cardiodectes medusaeus. This is itself an ectoparasite of the Northern lampfish (Stenobrachius leucopsarus) in the family Myctophidae. The copepod attaches itself to the bulbus arteriosus of the fish. Such a parasitic chain is known as hyperparasitism. The actions of the copepod castrate its fish host. Both male and female fish do not reproduce and seem to grow faster when attacked by the copepod and it seems to have a negligible energy demand from them. The hydrozoan parasite castrates the copepod, a process called hypercastration.

Southern bluefin tuna

The southern bluefin tuna (Thunnus maccoyii) is a tuna of the family Scombridae found in open southern Hemisphere waters of all the world's oceans mainly between 30°S and 50°S, to nearly 60°S. At up to 2.5 metres (8.2 ft) and weighing up to 260 kilograms (570 lb), it is among the larger bony fishes.

Southern bluefin tuna, like other pelagic tuna species, are part of a group of bony fishes that can maintain their body core temperature up to 10 °C (18 °F) above the ambient temperature. This advantage enables them to maintain high metabolic output for predation and migrating large distances. The southern bluefin tuna is an opportunistic feeder, preying on a wide variety of fish, crustaceans, cephalopods, salps, and other marine animals.

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