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Lab 4 : Fish Systems Introduction Today in lab, we will be examining the many organ systems of the Atlantic herring (Clupea harengus). We will look at Reproduction, Respiration/Circulation, Feeding/Digestion and Locomotion. The lab will introduce new concepts, as well as reviewing some older ones. The Atlantic herring is a pelagic schooling fish found in great abundance in the North Atlantic Ocean. In Nova Scotia, the Atlantic herring is fished during the fall for roe (eggs) which is shipped primarily to a Japanese market. Herring are also used for lobster bait. Herring eat plankton and must filter the small organisms out of the water. External Morphology Morphology refers to the external shape and features of an object/organism. Anatomy is used to refer to the internal location and arrangement of organs and features. Morphology Examine the fish that you and your partner share. When trying to identify fish to species level, the overall body shape, fins, jaw and eye placement are important. Identify the different structures of your herring. Figure 1. Typical Fish Fins and Features 4 Median Paired 1 – Operculum 2 – Lateral Line 3 – Dorsal Fin 4- Cloaca (Anus) 5– Caudal Peduncle 6- Caudal Fin 7-- Anal Fin 9—Pelvic Fin 10—Pectoral Fin Graham Bould. July 2006. Hector’s Lampfish. Wikimedia Commons. Name:___________________ Lab Section__________________ Internal Anatomy Reproduction Atlantic Herring, like most fish, use external fertilization, where eggs or sperm are released through the cloaca into the water. Find the cloaca of the herring. Shallowly cut the skin from the cloaca to the pectoral girdle. The first thing you will notice are paired gonads, in the females they will be reddish, in the males white. The female gonads contain thousands of small eggs (20 000 to 200 000 depending on size), or roe. The male gonads contain sperm in a milky substance, referred to as milt. Fish do not have separate exits for these reproductive cells, they are released in the cloaca where the intestines also empty. Before removing the gonads, see if you can follow the path the eggs or milt will follow through the cloaca into the water. Hdahlmo. December 2005. Wikimedia Commons. 1 – Liver 2 – Swim bladder 3 – Gonad (female) 4 – Pyloric caeca 5 – Stomach 6 – Intestine Figure 2. Internal Anatomy of a Fish After tracing this path, you may remove the gonads from the fish to allow you better view of the other organs. 2 Name:___________________ Lab Section__________________ Circulation and Gas Exchange Fish have a single loop closed circulatory system. The blood goes from the heart to the gills where it is oxygenated, then goes via the dorsal aorta to the body and returns to the heart through the postcardinal vein. Main artery Main vein Gills – counter current Heart Figure 3. Typical Fish Circulatory System Florida Center for Instructional Technology http://etc.usf.edu/clipart" Gas exchange takes place in fish via their gills. The gills are located on both sides of their mouths and are hidden by the gill operculum which protects the delicate structures from damage. The operculum is also used to ventilate the gills when fish are not moving. Find the gill operculum on your herring. Tap it to see how strong it is. Lift it and note the gills underneath. You should be able to count how many gill arches there are, each gill arch has gill rakers on one side and gill filaments on the 1 other. The lamellae on the filaments 2 are the functional respiratory elements. The filaments are usually a deep red colour because they are highly vascularized with networks of Figure 4. Gill Arch (1-filaments and 2-rakers) capillaries since this is the primary site of gas exchange. Fish allow water to flow through their mouths and out their opercula. As the water flows over their gills, they absorb oxygen into their blood through a counter-current exchange system. The oxygen-depleted water continues out through the gill operculum. Cut off the first gill arch and examine it. Identify the gill filaments, lamellae and the extra long gill rakers. There are a few dissecting scopes set up for you to examine the filaments, under higher power? If you continue your cut through the pectoral girdle towards the anterior end you should be able to find the triangle shaped heart of the herring. 3 Name:___________________ Lab Section__________________ Digestion Herring primarily eat zooplankton; do they have teeth? Imagine that you are a piece of plankton, starting in the mouth, use a blunt probe to follow the path the food would take. Take care to identify the various components of the feeding and digestive systems: a) mouth and gill rakers; b) esophagus c) stomach – site of primary digestion d) pyloric caeca – the finger-like organ contains many enzymes and assists in digestion of proteins and sugars e) liver – secretes fat digesting enzymes, and stores fat f) intestines – completes nutrient absorption g) anus/cloaca – location of waste release You may cut open the stomach if you wish to try and identify stomach contents. Figure 5: Source: The Visual Dictionary http://www.infovisual.info. Reproduction rights reserved and strictly limited. Locomotory System Using primarily the blunt probe, carefully remove the skin from one side of the fish. Examine the muscle structure. You should see very distinctive blocks of muscles. These blocks are myotomes, they are divided by myosepta. Fish have both red and white muscle, as you learned in the video in class. Cut a cross-section through the tail behind the anus, identify sections of red and white muscle in this section. What are the functions of the different types of muscle? What type of fibres make up each colour of muscle? You also learned in the video that most fish have gas-filled swimbladders which help them maintain buoyancy in the water. Some fish have only a gas 4 Name:___________________ Lab Section__________________ gland which produces gas that fills the bladder (physoclistous). Other fish, including herring, get gas into their swim bladders by “gulping” air into the gut which then enters the swim bladder via a pneumatic duct (physostomous). Try and find the pneumatic duct between the intestine and the swimbladder. Swimming Movement and Gait Changes Many fish propel themselves by generating backward moving waves of contraction on their bodies that extend to the caudal fin. This type of swimming (or gait) is called Body or Caudal Fin (BCF) locomotion, and is powered by the red and white muscles forming most of the body of the fish. Fish can also use their median and/or paired fins to propel themselves and this is called MPF locomotion. These are powered by separate muscles operating the fins. Many fish use one form of locomotion at one speed and change ‘gaits’ to another form as the speed changes. The burst and coast gait is used by many fish to reduce the cost of locomotion when moving over long distances. Observation of Swimming Observe the different swimming gaits used by the live fish in the aquarium at the back of the lab. You should be able to see fish using all the gaits in the chart below. Students should not do this all at the same time. Complete at any point during the lab. Swimming Gait (BCF or MPF) Fins used Station holding -remain in same location ‘Saunter’ -move slowly Sprint -move quickly Burst and coast -sprint followed by a glide 5 Name:___________________ Lab Section__________________ Assignment - Hand in at the end of lab. Locomotion 1. From your observations of the fins and body undulations used during the burst and coast gait, hypothesize why it is often used by fish to reduce the cost of locomotion. Circulation and Gas Exchange 2. What circulatory or gas exchange adaptations (at least 3 points) might you expect between an active pelagic fish, such as herring, but not in a more sedentary bottom-dwelling fish such as a sculpin? Digestion – one sentence answers only. 3. Why do herring have such long gill rakers? 4. What benefits (other than enzyme secretion) might the pyloric caeca provide in terms of digestive abilities? 6