Anatomy and Life Cycle of Chordate Animals - Research Paper

Introduction

The Chordate animals include animals of the phylum Chordata. Within the period of their life cycle, the chordate animals in this phylum are defined by five major anatomical features (Rychel & Swalla, 2007). These features include an endostyle, dorsal nerve cord, post-anal tail, pharyngeal slits, and a notochord (Rychel & Swalla, 2007). Also, the chordate animals are bilaterally symmetric as they have a circulatory system, coelom, and a metameric segmentation. Within the chordate species, it is divided into three primary subphyla, which include; Cephalochordate, Tunica, and the Vertebrata. Within the Tunica, also defined as Urochordata they include salps and sea squirts, the Cephalochordate include lancelets, while the Vertebrata include mammals, birds, fish, amphibians, and reptiles (Rychel & Swalla, 2007). However, this paper will provide research on fish as a chordate animal. In the article, the taxonomy, ecology, physiology, diet, reproduction, habitat and range, population, and behavior will be discussed on fish.

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Chordate Animal: Fish

The gill-bearing animal is represented in the phylum Chordata found in both salt and fresh waters in the universe. Often, fish is considered as the sister species to the tunicates as they together form the olfactory (Villeger et al., 2017). The living animal ranges from the jawless hagfishes and lampreys through the sharks, rays, and skates to the bony fishes. In the species, most of the fish are cold-blooded except the opah species (Lampris Guttatus), which is warm-blooded (Villeger et al., 2017). As a member of the phylum Chordata, fish share the different features in other vertebrates. With the tetrapod emerging deep within the fish species, the shared features include the gill slits, notochord, tail, ad the dorsal hollow nerve cord. From the fossils record, early fish are characterized by the ostracoderms, small, armored, and jawless fish. However, the jawless fish species are extinct, with the lampreys approximating the ancient fish with pre-jaws. In different ways, the diversity of the fish species could indicate fish evolution.

Fish Taxonomy

In the classification of fish, they are classified within the Vertebrata Subphylum. For an animal to be defined as a vertebrate, the backbone or vertebral column is essential as it encloses, protects and supports the spine (Keat-Chua et al., 2017). However, fish can be classified deeper into three classes. The first class includes Class Agnatha (Jawless fish) and entails subclass Ostracodermi (armored fish) and subclass Cyclostomata (lampreys and hagfish). The second class requires the Chondrichthyes, which involves the cartilaginous fish categorized under subclass Holocephali (such as chimaeras and other extinct species) and subclass Elasmobranchii (such as sharks and rays). The third class involves Osteichthyes composed of bony fish. Class Osteichthyes includes subclass Sarcopterygii (such as fleshy finned fish and other tetrapods) and subclass Actinopterygii (such as ray-finned fish). According to the different studies, there are approximately more than 30,000 species of the Class Osteichthyes or bony fish, 600 species of the Chondrichthyes class, and up to 50 species of the jawless species (Keat-Chua et al., 2017).

Additionally, the bony fish are deeper classified into two primary groups defined as the lobe-finned group (such as lungfish) and ray-finned groups (such as catfish and perch). In as much as the different fish species are categorized into three major groups, it is critical to note that the development of the phylogenetic nomenclature has offered more divisions. Some of the divisions include Class Pteraspidomorphi, Class Anaspida, Class Hyperoartia, Class Myxini. Class Thelodonti, Class Cephalaspidomorphi, and Class Conodonta. Further, there are other jawed vertebrates (Infraphylum Gnathostomata) such as the cartilaginous fish, armored fish, spiny sharks, and the bony fish as well. The different fish classes account for approximately more than half of the vertebrates (Keat-Chua et al., 2017).

Fish Ecology

Within the fish ecology, it described the movement patterns, stock structure, food dynamics of the exploited fish species populations, and the life-history traits. The fish ecology is significantly influenced by the various physical properties of water, such as miscibility as a solvent, heat capacity, density, among others (Helfman et al., 2009). In the structure of water, it is denser than air, which means that fish need a minimal amount of energy and matter in the maintenance and development of their bodies. The gas-filled bladder in most fished allows them to keep a neutral buoyancy in deep ranges of water depth. With the high-density water, it causes efficient transmission of sound better than air. The slow sound attenuation of noise in water increases the possibility of sonic signals to be transmitted over extended ranges of distance. The inner ear and acoustic-lateralis help fish perceive sound as they involve pressure receptors in the body flanks and head scales. The swim bladder functions as the eardrum as the sound is transmitted from the body wall. However, since most fish are ectothermic and can exploit temperature gradients, this helps increase their utilization of energy (Helfman et al., 2009).

In consideration of the fish movement patterns, the pattern and scale of their movement vary among the different species. For instance, some of the significant directed and most prolonged shifts by anadromous in the North American ricers migrate from streams to oceans and later migrate to the natal streams to spawn (Winemiller, Agostinho, & Caramaschi, 2008). For most of the species, they do not move into the sea but tend to establish habitats and occupy ranges of various amounts of time. The fish movement is dependent on fish history and their environment. Furthermore, there are differences involved with life-history traits of the fish, such as size at reproduction, age, and the spawning timing. Generally, fish movement is essential and significant in the breeding and survival of fish.

Fish Physiology

The fish physiology defines how the different components of fish work together to ensure that the fish lives. In most of the cases, fish physiology is connected in anatomy to ensure that one understands how the organs interact with each other in the living vertebrate (Val & Randall, 2005).

Respiration

Since these are water animals, most of the fish exchange gas through the gills located on the pharynx sides. As the gills comprise of structures such as threads names as filaments, they consist of a networked capillary structure that offers the surface for carbon dioxide and oxygen exchange. The fish pulls water through the mouth and pump it to the gills. However, in different species, blood flows in the opposite direction to the sea, causing countercurrent exchange. In the bony fish, gills are located on the side covered by the operculum (bony cover), which helps regulate the water pressure to enhance gill's ventilation (Grosell, Farrell, & Brauner, 2010). For the cartilaginous fish, they have gill slits outside their bodies with spiracles (modified slit), and water flows through the mouth to the gills defined as ram ventilation. The hagfish and lampreys lack gill slits and have a circular opening as a spherical pouch (Grosell, Farrell, & Brauner, 2010).

Besides gills, fish from various species that can stay on the surface breath air, such as the amphibious fish. As the fish can breathe through different mechanisms, their skins could absorb oxygen. For example, catfish with the Class Callichthyidae, Loricariidae, and Scolopacidae use their digestive tracts to breath. Primarily, breathing air among some fish species is based on the occurrence that the fish live in shallow and seasonal waters. It means that particular fish that depend on dissolved air could die (Zaccone, Lauriano, Capillo, & Kuciel, 2018). Air-breathing fish species could be categories as facultative air breathers and obligate air breathers. According to the facultative air-breathing fish (like catfish), they only breathe if they need and use their gills while, obligate air-breathing fish (like the ling fish) have to breathe often to avoid suffocation (Zaccone et al., 2018).

Circulation

Within the circulation system of fish, it involves a closed-loop system as blood is pumped in a single loop in the body. As the fish own four sections, the first is the sinus venosus (thin-walled sack) that helps blood flow onto the second section, the atrium, which sends blood into the ventricle. Later, the ventricle pumps blood to the bulbus arteriosus connected to the aorta allowing oxygenation and then out of the fish's heart (Farrell, 2011).

Digestion

In most fish, the food ingested in the mouth is broken into the esophagus. Within the stomach, pyloric caeca (finger-like pouches) process, the food, and nutrients are absorbed. The lungfish, hagfish, chimaera, and lamprey lack a stomach, which means that the esophagus cuts into the intestines directly. These fish species have to consume diet requiring little or no storage. Moreover, there is no small intestine in fish such as lungfish and sharks hence forming spiral intestine. Most of the digestion occurs within the intestine (Stevens & Hume, 2004).

Excretion

Through the gills, some of the waste is diffused while most of the fish excrete nitrogenous waste as ammonia. In salty water fish, water is lost due to osmosis, and the kidneys return the water while in freshwater fish, water is gained through osmosis, and the kidney enhances excretion.

Sensory and Nervous System

In the fish brain, it is divided into five main sections. The olfactory lobes which are the front brain that receives and processes data, two-lobed telencephalons responsible for the olfaction, and the diencephalon, which is concerned with homeostasis and hormones. Within the structure, the midbrain containing large optic lobes leads to the cerebellum that represents the most substantial part of the brain. The hindbrain is responsible for the balance and swimming of the fish. In the stem of the brain, there is the myelencephalon that helps control muscles (Kotrschal et al., 1991).

The nervous system of fish functions as the core mechanism that coordinates the body activities of the fish. The primary integrating mechanism consists of the spinal cord and the brain, which is the central nervous system. For the peripheral nervous systems, it accumulates nerves that link the spine and the brain to other organs and conveys sensory data from receptor organs to others. In the vision of the fish sensory system, they have eyes similar to terrestrial vertebrates, but the lens is spherical. About sense, fish sense with the use of the lateral lines (Fay & Tavolga, 2012).

Fish Habitat and Range

Fish inhabit almost all available and conceivable aquatic habitations (Gratwicke & Speight, 2005). For instance, the bony fish are located in temperate, polar and tropical seas, and other freshwater bodies as well. The different fish species adapt to different habitats such as coral reefs, kelp forests, rivers, under the sea ice, deep oceans, rocky shores, and other fresh and saltwater environments. Pelagic fish inhabit the open oceans, lungfishes hibernate, among other different functions of the species. Generally, since fish rely on oxygen dissolved in water, the habitats vary based on their adaptation. In the fish ranges, there are influenced by the migration practices. For example, the bony fish are small range. While other fishes migrate over long distances (Gratwicke & Speight, 2005).

Fish Diet Habits

Based on the different species and groups, fishes have a wide range of diets and preferences. For example, some fish are herbivorou...