Fish Pt. 1

1. What characteristics distinguish the hag fishes and lampreys (superclass agnatha) from all other fishes?

Firstly, the most obvious characteristic of agnathan fish is that they lack jaws (hence the name Agnatha, which means ‘without jaws’). This is in contrast to other fish groups such as Chondrichthyes (sharks and rays), Actinopterygii (ray-finned fish) and Sarcopterygii (lobe-finned fish) which all have jaws. Instead of jaws, hagfishes and lampreys have a circular mouth lined with numerous sharply pointed teeth which they use to grasp onto and suck fluids from their prey.

Secondly, Agnathan fish also lack paired fins. While most fish have two sets of paired fins right behind their gills, hagfish and lampreys have only a single unpaired dorsal fin running along their backs. They also lack any bony structures, instead having cartilaginous skeletons like sharks, rays and other cartilaginous fish.

Another notable feature of hagfishes and lampreys is the presence of a notochord throughout their lifetime. The notochord is a rigid, hollow dorsal nerve cord that forms most of the axial skeleton in vertebrate embryos. In most fish species this is eventually replaced by vertebrae, but in hagfishes and lampreys the notochord persists throughout their lives as the primary support structure for their bodies.

Finally, unlike other fish, Agnathan fish also do not possess scales on their body. Instead, hagfishes have a slimy, scaleless skin that secretes copious amounts of slime when agitated, while lampreys have small, tooth-like structures called dermal denticles embedded in their smooth, scaleless skin.

2. Describe the life cycle of Sea Lamprey Petromyzon marinus and the history (route) of its invasion of the Great Lakes.

The Sea Lamprey Petromyzon marinus is a parasitic fish species that has a complex life cycle, involving several stages of development. The adult Sea Lamprey enters freshwater rivers to spawn during spring, where their larvae hatch and develop into ‘ammocoetes’, a worm-like form that are filter feeders that burrow into soft sediments of the riverbeds. After 3-7 years in the developmental stage, they metamorphose into parasitic juveniles known as ‘macropthalmia’, where they actively search out a large host fish to attach to and suck blood from the fish’s body. The Sea Lamprey matures over 12-20 months while they feed on the host fish, which results in the death of the host fish.

The Sea Lamprey Petromyzon marinus has a complex life history with various stages that make it challenging to manage and prevent its impact on ecosystems. The Great Lakes are an ideal habitat for the species due to the favorable temperature, ample food sources, and the absence of natural predators. The Sea Lamprey was first reported in a Great Lake, Lake Erie, in 1921. Still, its introduction to the Great Lakes probably occurred through an artificial canal that connected the Atlantic Ocean to the Great Lakes in the 1820s, which enabled the Sea Lamprey to bypass natural barriers to reach the Great Lakes.

Once the Sea Lamprey Petromyzon marinus became established in the Great Lakes, their population grew exponentially, posing significant threats to the fisheries in the Great Lakes. The Sea Lamprey is known as an ‘invasive species’ because they were introduced to a new habitat, the Great Lakes, and they negatively impact the native species and the environment by being overly predatory. There is no practical solution to eradicate the Sea Lamprey from the Great Lakes due to the species' complex life cycle and their ability to inhabit both freshwater and saltwater environments. Therefore, preventing its invasion through measures such as canal management and habitat restoration is critical in controlling its population in the Great Lakes.

3. What does Gnathostomata mean and who belongs to this group?

Gnathostomata: Gnathostomata is a term used to describe a group of vertebrates that possess a hinged jaw, which is composed of two pairs of jaws. This group includes animals such as fish, amphibians, reptiles, birds, and mammals. Gnathostomata is derived from the Greek words "gnathos," which means jaw, and "stoma," which means mouth.

Jawed fishes: Jawed fish, also known as gnathostomes or jawed vertebrates, are fish that have a hinged jaw. This group includes three classes of fish: Chondrichthyes (cartilaginous fish), Actinopterygii (ray-finned fish), and Sarcopterygii (lobe-finned fish). Some examples of jawed fishes include sharks, rays, salmon, and lungfish.

Amphibians: Amphibians are a group of animals that are characterized by their ability to live on land and in water. They possess a hinged jaw and a bony skeleton. The three orders of amphibians are Anura (frogs and toads), Caudata (salamanders), and Gymnophiona (caecilians).

Reptiles: Reptiles are a group of animals that are characterized by their scaly skin and the presence of a hinged jaw. They include animals such as snakes, lizards, turtles, and crocodiles. Reptiles are ectothermic, meaning that they regulate their body temperature by taking in external heat sources.

Birds: Birds are a group of animals that are characterized by their feathers, wings, and beaked jaws. They belong to the class Aves and are the only group of animals that can fly. Birds also have a unique respiratory system, with air sacs that allow them to take in air continuously.

Mammals: Mammals are a group of animals that are characterized by their hair or fur, mammary glands that produce milk for their young, and a hinged jaw. They include animals such as humans, dogs, cats, and whales. Mammals are endothermic, meaning that they regulate their body temperature internally.

4. Give examples of chondrichthyes and why do shark have spiracles, why to rays have spiracles.

Chondrichthyes, commonly known as cartilaginous fish, is a class of fish that includes sharks, rays, and chimaeras. These fish have a cartilaginous skeleton, five to seven gill slits on the sides of their heads, and a placoid scale (also known as a dermal denticle) skin.

Sharks, being a classic example of Chondrichthyes, have spiracles, which are small openings behind their eyes that connect to the pharynx. The spiracles act as a supplementary breathing mechanism, which allows the sharks to breathe even when their mouths are closed, and water cannot enter through their gills. For instance, bottom-dwelling sharks like the nurse shark can use their spiracles to pump water over their gills while resting on the seafloor, preventing sand or sediment from entering their gills.

On the other hand, the rays have a flattened body that allows them to rest on the seafloor, which requires protection for their gills. They have their spiracles located on top of their heads, which creates a pressure gradient that induces water to flow over the gills. Rays dig into the sand or mud with their mouths, push water via spiracles, and out through the gill slits located at the bottom of their body, allowing them to breathe without disturbing the seafloor. This mechanism helps them obtain oxygen without disrupting the fine sand particles or becoming buried in the sediment, thus making them well-equipped for their habitat.

5. Describe the lateral line system and ampullary organs of lorenzini in sharks and explain their function.

The lateral line system and ampullary organs of Lorenzini are sensory structures that allow sharks to detect and locate prey, as well as sense changes in their environment. The lateral line system is a series of canals and sensory cells that run along the sides of a shark's body, from the head to the tail. These canals are open to the water and are lined with tiny hair-like structures called cilia. When water moves over the cilia, it creates a nerve impulse that is sent to the shark's brain, indicating the location and movement of nearby objects or organisms.

The ampullary organs of Lorenzini are specialized sensory structures located in the head of sharks. These structures are made up of a series of small, jelly-filled canals that are connected to sensitive cells. These cells are extremely sensitive to electrical fields, and allow sharks to detect the bioelectric fields given off by the muscles and nervous system of other animals in the water. This ability to sense electrical fields is particularly useful for locating prey that may be hiding or moving in dark or murky water.

Together, the lateral line system and ampullary organs of Lorenzini allow sharks to navigate their environment, locate prey, and sense changes in their environment such as changes in water temperature or pressure. These sensory systems are crucial to the survival of sharks, allowing them to hunt effectively and avoid danger.