TOWARDS LEVEL 2
PROFESSIONAL DEVELOPMENT - FISH BIOLOGY
A Level 2 coach should be capable of coaching and administering the CAST - Core Angling Skills and Techniques - scheme to CAST Level 6. Most of the information required for this will be covered by the coach's own knowledge and angling skills but there may be some areas which require a little research, e.g. fish biology, river and lake topography, fish diseases and parasites and invasive species.
This short series of articles is intended to help with this, with each module linked to a short quiz to see how much information has been retained.
MODULE 1 - FISH BIOLOGY
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In many ways, the internal organs of a fish mirror the functions of our own albeit their shape and size is of course very different. Just like ours, the heart of a fish pumps its blood around the body but, unlike ours, it has only got one ventricle and atrium. The blood is pumped from the ventricle to the gills, to be oxygenated, and is then pumped around the rest of the body before reentering the heart via the atrium. It is then transferred to the ventricle for the whole process to start again.
The nostrils of the fish, also called nares, enable the fish to detect odours that are often far away from where the fish is lying. Species like catfish have a sense of smell that is extremely well developed. They have been recorded as able to detect different substances where only a miniscule amount has been added to the water, with some experiments recording an incredible ratio of one part substance to ten billion parts water. It is no wonder that they can successfully scavenge in the most light-deprived areas of water!
The gills of the fish enable it to remove oxygen from the water whilst simultaneously getting rid of waste like carbon dioxide and nitrogen.
The stomachs of fish enable them to process food and remove nutrients from what they have eaten. However, unlike us, some species do not have stomachs at all with short intestinal tracts that do the job instead. Such species, of which the ballan wrasse is a UK example, are referred to as agastric, literally stomachless!
The liver of a fish is essential to its digestion. It creates enzymes that break down fats and simultaneously serves as a storage area for fats and carbohydrates. It also plays a major part in the destruction of old blood cells and in maintaining proper blood chemistry, not to mention helping to get rid of waste nitrogen.
The intestines of a fish perform several tasks, the most important of which is helping it to digest and absorb nutrients from its food. The intestine is also critical for water and electrolyte (chemicals such as salt, potassium, calcium and chloride) balance and endocrine (hormones created within the body) regulation relating to digestion, metabolism and immunity. For species that migrate from saltwater into freshwater and back again, the electrolyte balance is crucial. In fresh water, their blood is saltier than their surroundings, which requires some adjustment to the electrolyte balance, while in salt water the opposite is true. A migrating fish therefore has to contend with changing from purging itself of excess salt in the sea to absorbing it in fresh water to maintain a proper balance.
As an angler, this is often seen in species like bass and flounders when you are fishing a long way up an estuary. Fish cannot make such adjustments automatically so, after a period of heavy rain, when the salinity of the water is greatly reduced, they run down the estuary, ahead of the rainwater, towards the sea, vacating their previous haunts. Similarly, on a high Spring tide, when the salinity of the water is greatly increased, they will travel further up the river than was previously the case. Species such as this are termed euryhaline, able to withstand a wide range of salinity, and include salmon and the European eel (Anguilla anguilla).
When we think of a bladder, especially a urinary bladder, we think of it as storage for urine. In freshwater fish, it is a thin-walled organ that is used for electrolyte exchange rather than storage. Think of it as a two way filter responding continually to the fish's needs. Scientists think the difference came about when creatures evolved to walk on the land. A continual, unbroken trail of waste material would be easy for a predator to follow. By contrast an intermittent trail caused by storing waste and then releasing it periodically would be much harder to track.
No surprises for the gonads in fish, however. Their job is simply to produce sperm in preparation for mating. The brain also holds few surprises, controlling input from the olfactory lobe (smells, records and responds to chemical input), the optic lobe (vision and yes, fish can see in color, some can even see in infra red), the cerebellum (coordinating movement and maintaining balance) while other parts control internal organs, coordinate input from other parts of the brain and are linked to the lateral line which detects movement and controls balance.
As for the kidneys, they are one of the body organs involved in excretion and regulation of the water balance within the fish. They are paired organs found in the body cavity either side of the backbone and help the fish maintain its electrolyte levels. Remember that seawater contains more dissolved salts than the body of a fish while freshwater contains less.
The last organ that I am going to look at is the swimbladder. The main job of this gas-filled organ is to maintain the buoyancy of the fish in response to the pressure that surrounds it. It also plays a part in respiration.
Looking at the external features of a fish first of all, each of the fins is designed for a specific task. The dorsal fins, for example, increase the lateral area of the fish. This helps to make it stable in the water when it is swimming albeit with slightly increased drag. Some species that have a long, continuous dorsal fin can ripple it all the way down - just enough to give a slight movement either forwards or backwards. On other species, like the European bass (Dicentrarchus labrax) some of the dorsal fin rays are hard and sharp, a deterrent against predators, while in other species, like the lesser or greater weever fish, this defensive feature is taken even further with the addition of venomous spines that can inflict a painful injury.
Most of the propulsion for a fish comes from the tail, known as the caudal fin, which is often divided into upper and lower lobes. It attaches to the peduncle, often referred to as the caudal peduncle, which is the tapered area behind the dorsal and the anal fins. Fast swimming fish, like mackerel (Scomber scombrus) have narrow, highly-tapered peduncles to which finlets, sometimes called adipose tufts, are attached to help them swim effectively at speed. Ambush predators, like bass, have much wider peduncles to give them the short burst of speed necessary to rush from their hiding places and intercept their prey.
The anal fin's function is to help keep the fish stable. This is usually found on the lower half of the body, just in front of the tail. Some species, like catfish (Silurus glanis) and salmon (Salmo salar) have a top, rather soft, fleshy fin set above it which is called an adipose fin. Scientists are not exactly sure what this fin does though some believe that it helps the fish respond to touch, sound and changes in pressure. After suffering the loss of an adipose fin, fish have been observed beating their tails eight percent faster than they did before.
At the front of the lower body, there are two fins called the pelvic fins. These are there to help the fish change depth - either upwards or downwards - but also help it to make sudden stops or sharp turns. In some species, like gobies (Pomatoschistus microps) these fins fuse together to make a sucker that the fish can use to cling to the rocks.
Pectoral fins are often tucked tightly to the sides of the fish, especially when swimming at speed, but they can be flared to give lift, a feature that helps sharks swim near the surface and which has been exaggerated even more in flying fish to propel them above the waves. On some species, like angler fish (Lophius piscatorius) the pectoral fins help them to 'walk' along the bottom, perhaps a stealthy strategy to help them change their position of ambush without giving themselves away!
The gill covers of fish, the operculum, cover and protect the gills whilst simultaneously allowing them to function. Other parts of the fish that are often referred to are the maxilla - the upper jaw - and the maxillary, which is a plate covering the hinge where the upper and lower jaws meet at the side of the head. Some fish, like sharks and flounders (Platichthys flesus) have spiracles, openings set behind the eyes where they can breathe in oxygenated water without the use of their gills. In some cases, this helps them to rest on the bottom without swimming while in others, like flounders, they are believed to help increase the fish's olfactory ability - their sense of smell.
Some species also have a second set of jaws and teeth in their throats, referred to as pharyngeal teeth. In species like ballan wrasse (Labris bergylta) these help them to make short work of hard-backed crabs and shellfish on their journey to the stomach. Other species, like cyprinids, members of the carp family, lack teeth in the oral cavity but do have a set of well developed jaws and pharyngeal teeth in the gill arches where they can crush food items and help to pass them along to the stomach. In some fish, they are at the top and the bottom and in others, like most cyprinids, they are at the sides. Ironically, species such as rays do not possess them even though there are many ray species that have to crush their food. You would have thought that they would find them useful!
At the end of each module, there is a link to an online quiz that coaches can take when they feel confident of their ability to pass.
Candidates will need to record their name, coaching status and email address when prompted at the end of the quiz. If you pass, a certificate will then be forwarded to you for printing and adding to your coaching CPD folder.