Zoology 511 Spring 2006 Lab 1 - Fish Anatomy Goals Identify structures important in the identification of species Acquire basic understanding of the anatomical structure of fishes Introduce concept of functional morphology Readings Helfman et al. 1996. pg. 37-50. External Anatomy (lamprey, dogfish, white perch) Most of our fish identification will be based on external anatomy. Therefore it is essential to be able to identify key characteristics of fish external anatomy. In the field, the coloration of fish can be important to their identification. What notable skin colorations do you see? Do you see a pattern in the fish’s coloration? If so what purpose might that pattern have to the ecology of the fish? Next, you'll need to identify the fins: Caudal, Pectoral, Pelvic, Anal, Dorsal, and Adipose (only on some fish). Also, identify the claspers on the dogfish (if present). Use the diagrams below as a guide to identify these fins. Note that fins consist of rays (Teleostei only; white perch) projecting from the body which are typically connected by a membrane. The number of rays on the fins is often an important characteristic in fish identification. Practice counting the number of dorsal fin rays and anal fin rays. How many rays does the white perch have on its anal fin? How do the dorsal fins on the lamprey and shark differ from the white perch? Find the following structures on the lamprey (use the diagrams below as a guide to identify these structures). Pineal Eye External Gill Slits Leaflike Lamellae Cloaca Buccal Funnel Horny teeth Nostril Find the following structures on the dogfish (use the diagrams below as a guide to identify these structures). Spiracle Fin Spine External Gill Slits Zoology 511 Spring 2006 Find the following structures on the white perch (use the diagrams below as a guide to identify these structures). Operculum Maxilla Pre-maxilla Branchiostegal Rays Anus Nares Gills Scales Caudal Peduncle Lateral Line Look at the lateral line of the white perch under a magnifying glass. Remove a lateral line scale and look at it under a dissecting scope, and reexamine the lateral line where you removed the scale. What does the lateral line consist of? What do you suppose its function is? Remove some white perch scales (from somewhere other than the lateral line) and examine them under the dissecting scope. Draw a picture of one: Examine the gill area of the white perch. Lift and then lower the opercula; do any other structures move away from the main body of the fish? Which ones? Distend, or stretch the lower jaw of your perch. Notice how flexible the skin is on the posterior edges of the maxilla-premaxilla process. Put your finger inside the perch’s mouth. On what surfaces do you feel some kind of dentition? Internal Anatomy (dogfish, white perch) Caution - your scalpel blade is extremely sharp. Take time to check the location of all your fingers before you start an incision! Observe the prepared dissection of the dogfish and identify these internal structures. Esophageal Papillae Rugae Pancreas Rectal Gland Rectum Ileum Pylorus Gall Bladder Liver Stomach Spleen Colon Spiral Valve Duodenum Common Bile Duct Notice the size and oiliness of the dogfish liver. The oil is called squalene and hence the scientific name of the dogfish (Squalus acanthias). Can you think of an additional function of the dogfish liver besides its normal function, considering its size and oiliness? Zoology 511 Spring 2006 What purpose does the spiral valve have in the intestine of the dogfish? Before you begin any incisions on the white perch, weigh the fish. Expose the oral cavity and pharynx of the white perch by making a shallow horizontal cut from the posterior corner of the mouth to the posterior edge of the operculum. Be careful not to cut through the gill membranes beneath the operculum. For the white perch, it is easiest to use scissors to cut through the operculum. Identify the gill arches, gill filaments and gill rakers. Any ideas on the function of the gill rakers?? (Take an entire gill arch out and look at it under the scope for a closer look.) Expose the abdominal cavity and pericardial cavity of the white perch: first, gently descale the ventral surface of the fish, and then make a shallow longitudinal incision extending from the anus to between the gill arches. You’ll need to use scissors to get through the pelvic fin girdle. Now, make a vertical cut from the anus to the lateral line, and another vertical cut from the abdominal cavity along the posterior edge of the operculum. The abdominal cavity is lined by a thin membrane called the peritoneum. Identify the following features: Heart Stomach Liver Intestine Kidney Gonads Fat deposits What sex is your fish? The gonadosomatic index (GSI) is the ratio of the gonad weight to the fishes’ total weight. Remove the gonads from your fish. At the front of the class is a scale. What is your fish’s GSI? Now, make an incision parallel to and dorsal to the first cut, so that one half of the left side of the fish is now exposed. This should give you a good view of the gas bladder (may not be visible, but look for the cavity anyway). Zoology 511 Spring 2006 On the other side of your fish, starting at the caudal peduncle, delicately cut under the skin. You want to remove the skin (not just the scales) and expose the muscle tissue. Continue up to the opercle or as far as you can, being careful to remove the skin only. Try to identify these tissues (use the diagrams below as a guide): Hypaxialis Epaxialis White muscle tissue Red muscle tissue If you have time, try to shave away muscle from the area around the spine to expose the vertebrae; do this near the abdominal cavity AND at the caudal penduncle. There are two different kinds of vertebrae in a fish: abdominal vertebrae and caudal vertebrae. What differences do you notice between them? Using a probe, see if you can locate the hemal and neural canals on a caudal vertebra. Deposit your fish and its parts in the trash can at the front of the room. Wipe down your lab bench, rinse off your instruments, and wash your hands well. QUESTIONS (Answer in one or two short sentences and turn in next week) 1. Answer these statements TRUE or FALSE about the white perch you dissected today: a. b. c. d. The pelvic fins are ventral relative to the pectoral fins. The caudal fin is located anterior relative to the dorsal fin. The anal fin is located posterior relative to the caudal fin. The dorsal fin is dorsal relative to the lateral line. 2. Sharks and rays (chondrichthyes) possess a series of gill slits through which water is passed. In contrast, perch possess a more elaborate gill anatomy consisting of the operculum and brachiostegal rays. Speculate how the presence of the operculum and brachiostegal rays enhance respiration for teleost fish. 3. How would you expect the gill rakers of a planktivore (plankton-eater) to differ from those of a piscivore (fish-eater)? Why? Zoology 511 Spring 2006 Fish Anatomy Diagrams The following diagrams will help you identify external and internal structures of fishes. Below is a picture of a snook (Centropomus undecimalis), from McClane (1978). Use it for help with external anatomy. Pictured at right is a typical salmonid, taken from Cailliet et al. (1986). Zoology 511 Spring 2006 Below is a picture of the musculature of a salmonid. Figure taken from Cailliet et al. (1986). Below is a picture of two vertebrae: a) abdominal vertebra; b) caudal vertebra. From Cailliet et al. (1986). Zoology 511 Spring 2006 Below is a picture of the arrangement and structure of gill rakers and gill arches of a bony fish (Cailliet et al. 1986). Below is a diagram of the external anatomy of the Pacific lamprey (Lampetra tridentate) taken from Cailliet et al. (1986). Zoology 511 Spring 2006 Below is a diagram of the internal anatomy of the Pacific lamprey (Lampetra tridentate) taken from Wessells and Center (1975). Below is a diagram of the external features of the spiny dogfish (Squalus acanthias) (Miller and Lea 1972). Zoology 511 Spring 2006 Below is a vental view of the internal anatomy of the spiny dogfish (Squalus acanthias) (Wischnitzer 1972).