The aim of this practical is to become familiar with the major internal features of teleosts (bony fishes)
The bony fish (Osteon = "bone"; "icthys" = "fish") are the most diverse and numerous of all vertebrates. Bony fish (Class Osteichthyes) are first seen in fossils from the Devonian (about 395 million years before present). They differ from most of the cartilaginous fishes in having a terminal mouth and a flap (operculum) covering the gills. In addition, most have a swim bladder, which is ordinarily used to adjust their buoyancy, although among the air-breathing fishes it is attached to the pharynx and serves as a simple lung. The skin has many mucus glands and is usually adorned with dermal scales. Their jaws are well developed, articulated with the skull, and armed with teeth. Although the skeleton of most is bone, that of sturgeons and a few others is largely made of cartilage. They have a two-chambered heart built on the same plan as the Chondrichthyes (two-chambered with a conus arteriosus and a sinus venosus). The sexes are separate, most are oviparous, and fertilization is usually external. There are two subclasses: subclass Actinopterygii (ray-finned fishes) and subclass Sarcopterygii (lobe-finned fishes).
The Actinopterygii is the larger of the two subclasses. These animals have slender fin rays supporting their fins and lack the odd appendages of the lobe-finned fish. Most actinopterygians have a symmetrical caudal fin (homocercal tail) and a swim bladder. This group includes most of the fishes with which you are familiar (bass, goldfish, guppies, sea horses, sturgeons, and tuna). Most of the specimens you will see belong to the superorder Teleostei. Teleosts are the most successful of the fishes (they make up 95% of all fish species). They are also the most modern of the fishes (they evolved about 65 million years ago). (Source: http://cas.bellarmine.edu/tietjen/images/bony_fish.htm)
The bony scales of a teleost are covered by a thin epidermal layer, within which are found the globular mucous glands. The bases of the scales are inserted into a layer of fibrous connective tissue. The fibrous layers and scales below the epidermis make up the dermal layer of the skin. The subcutis layer and muscle are located beneath the dermis. Fish scales are not plugged into skin like your hair (if you pull a hair out you don't destroy an overlying epidermis).
The purpose of this report is to familiarize with the major internal features of teleosts (boney fish) by dissecting the specimen of marine teleost .The information of the teleost that was dissected in this report is Barracuda which has the family name Sphyraenidae.
- Fish specimen (Barracuda)
- Hand gloves
- Preserved lamprey head cross-section
- Copy of Chiasson ''Laboratory Anatomy of the Perch '' .pg 34
Opened the abdomen of the specimen Barracuda by slitting along the ventral midline from just forward of the anus to the pelvic girdle The cut was deep enough to penetrate he body wall but not so deep as to damage the internal organs .At each end of the incision it was cut upward to the lateral line in order to flap of the flesh to expose the body cavity. The organs were teased out and sketched and labeled by identifying with the help of Chiasson pg 34.The parts targeted to locate were pigmented peritoneum, mesenteries, liver, esophagus, gizzard(if any),stomach(cardiac portion), pylorus , duodenum and small intestine ,rectum terminating at the anus, spleen, diffused pancreas , gall bladder, air bladder, paired gonads, genital duct, urinogenital sinus ,urinogenital papilla ,kidney and urinary duct.
After that an air bladder was dissected and located rete mirabile, oval was not located. The incision was further extended forward to expose pericardial cavity, which contained the heart The heart was sketched locating parts such as sinus venouses, atrium, ventricle, bulbus arteriosis.
Then carefully detached the frontal, parietal and other bones from around the brain. The brain was exposed and sketched the organs such as olfactory lobe, forebrain and optic lobe and cerebellum but could not locate medulla.
The jaws were also cut opened at the joints .The teeth type noticed and the roof of the mouth as well as lateral view of the mouth sketched. The stomach was also dissected and the contents investigated in order to confirm the fish diet.
Anatomy further proceded by cutting off the skin of Barracuda fish and muscle arrangements sketched. The two vertical cuts were made across the body and cross section of the muscles drawn.
Final step was to draw the lamprey head cross-section and compare with that of the jawed fish, Barracuda in this report. The parts of lamprey compared with jawed fish were oral disc, toothed tongue, single olfactory sac, gill pouches, or chambers, gill openings, and notochord
When the abdomen of the fish Barracuda was dissected , the organs observed were head kidney that started from head region and travelled all the way down the anus. It was located at the back of the air bladder and was maroon coloured. Heart was also observed it was two chambered and lobed. Liver was located just below the heart, in front of the stomach which was maroon in colour, the pancreas was incorporated into the liver and was not so noticeable, the well formed spleen was noticed that was located just below the air bladder.The air bladder was lobed shaped ,long and filled with gas .which is used for buoyancy purpose in fish so that fish can dive in and come back to the surface and respire efficiently and thus to stay at the current water depth without having to waste energy in swimming. The properly formed spleen indicated that Barracuda had very good immune system. The small intestine was long and tubular elongated along the fish length and is the last part of the digestive tract in fishes but digestive system terminates at the anus. The stomach of the fish was bent muscular tube in a "U" or "V" shape in order to aid for digestion and fit well in fish skeletal structure .A pair of gonads of similar size were also observed that was thread like and was elongated along the body .This indicates that Barracuda fish was from primitive teleost families. Urinary bladder was located underneath the end of the gas bladder attached with the kidney for water and ion transport from the salt water teleost such as Barracuda The diagram of the observation discussed is in the result section of the report in figure 1.
The air bladder was dissected and sketched as shown in the result section figure 2.The air bladder was single sacked and filled with gas indicating that the fish is from primitive fish families. It has flexible walls that contract or expand according to the ambient pressure. The walls of the bladder contain very few blood vessels.
When dissected ,it got punctured and the only part that could be located was rete mirabile .Rete mirabile was as small as a mass of blood spot .It is a wonder net,its not really a net but a looping bundle of arterial and venous capillaries associated with the gas gland that function as a counter current multiplier. The oval window was not noticeable which is a gas gland for adjusting gas pressure of the fish that can obtain neutral buoyancy and ascend and descend to a large range of depths. Gas bladder was located at the dorsal portion ,lobed and extending forward to the rear of the skull of the fish, giving fish lateral stability.
The incision was further extended to expose pericardial cavity that contained heart.The Aerial view of the heart is drawn as shown in figure 3 of the result section.The parts that could be located were afferent arteries that was present on ventral aorta, bulbous arterious, atrium ,ventricle, and hepatic sinus at the end of the heart.It was noticed that the heart is two chambered with artrium and ventricle .The ventral aorta was located which is divided into afferent branchial blood vessels. The arterial side of the heart is followed by a thickened muscular cavity called the bulbus arteriosus. Venous side of the heart is preceded by an enlarged chamber called the sinus venosus.
Furthermore, the dissection proceeded with detaching the frontal parietal and other bones from around the brain .The brain was exposed at the dorsal region and sketched as shown by figure 4 of result section. The organs observed laterally were 3 parts of the brain: forebrain, mid brain and hindbrain. The presence of forebrain indicates that the fish had ability to smell. The midbrain was large for the process of vision, learning, and motor responses. In this part 2 large optic lobe indicates that the fish uses eyes to hunt. The hindbrain consisted of medulla oblongata and cerebellum coordinates movement, muscle tone, and balance. Fast-swimming bony fishes usually have an enlarged hindbrain as was present in Barracuda fish dissected.
Barracuda fish had superior snout which is long and thin. It has large canine teeth in a lower jaw that projects beyond the upper jaw. There was no pharyngeal teeth in this fish.
Barracuda, Sphyraena barracuda, is a voracious marine predator that captures fish with a swift ram feeding strike. Barracuda can attack fish larger than the gape of their jaws, and in order to swallow large prey, can sever their prey into pieces with powerful jaws replete with sharp cutting canine teeth. (source: Justin R. Grubich, Aaron N. Rice, Mark W. Westneat,2007)
The stomach content had small fish in it that was partially digested .This confirmed that Barracuda fish are carnivorous.This Fish had vomerine and palatine teeths thus robust palatine bone embedded with large dagger-like teeth opposes the mandible at the rear of the jaws providing for a scissor-like bite capable of shearing through the flesh and bone of its prey.The diagram of barracuda mouth roof with vomerine bone and palatine teeth is labeled in figure 6 of lab report
When the skin of the fish trunk was removed the muscle of the trunk consist of a series of muscle blocks called myotomes. The myotomes usually resemble a sideways letter "W". A connective tissue called myosepta separates the myotomes A horizontal septum separates the myotomes into dorsal (top) myotomes and ventral (bottom) myotomes. (http://www.seaworld.org/animal-info/info-books/bony-fish/anatomy.htm).The digram of the fish muscle of the trunk and cross-section of muscle across vertical cuts of body is drawn as shown by figures 7 and 8 of result section.
The Lamprey head cross-section is drawn as shown by the figure 9 of the report.Lamprey belong to Class Agnatha consists of an ancient group of animals similar to fish but with some very noticeable differences. The agnathans lack jaws and paired fins. Instead of jaws, they have a cyclostomic (circular) toothed mouth with which they bore into the side of a fish and suck the blood of their victim. Agnathans lack an internal skeleton of bone while boney fish(teleosts) have boney skeleton .Some key features that makes Agnatha distict from jawed fish is that Agnatha has oral discs, toothed tongue,single olfactory sac, Seven or more paired gill pouches are present,gills have openings and the embryonic notochord persists in the adult.
Thus, the internal features of bony fish is in the specific structure and location as discussed based on their mode of life and its dietary pattern.
This practical report has enabled to familiarize with the internal organs of the bony Fish , Teleost. The location of each organs,its length , and structures exhibits the mode of life of the fish specimen(Barracuda).Hence,the location of air bladder in barracuda at dorsal end and it being lobed explains it belonging to the primitive fish families and also its stability in water .The brain structures where two big optic lobes were available indicated that the eyes are used for hunting .The three parts of brain determines its sense of smell , vision and locomotion. The jaw arrangements determined that it is a carnivorous fish and thus rams fish in mouth to feed. The difference in key features mentioned for Agnatha explains its difference with jawed fish such as Barracuda.