Marine Biology 250 - Fall 2019 Laboratory Assignment: Gross Anatomy Lab Objectives: 1. Visit the UW Fish Collection and learn about the wide array of fish body types and life histories 2. Learn about the external and internal anatomy in a variety of fishes. 3. Dissect a fish and examine how different organs and systems are laid out inside a fish 4. Work meticulously with a single fish to count and identify different structures 5. Discover that you can deduce life history information by a fish’s body shape, and that you can quantify body shape by looking at ratios 6. Compare your fish to a dogfish shark, and learn some of the differences between a bony fish and a cartilaginous fish INTRODUCTION Anatomy comes in two flavors - outside and inside. External anatomy describes the morphology or the shape of an organism. Internal anatomy looks at the shape and types of tissues and organs, and their placement. Before opening a fish, there are lots of things you can look at to decipher where (as in what habitat) the fish lived and how it made its living. Body shape, fin number and placement, tail shape, scale size, and the relative size of body parts are all specific to a species’ life history. Fast cruisers will look different than slow- moving benthic fish, which will look different from small-bodied maneuverers. Quantifying Morphological Differences To quantify the differences in life history as expressed through body shape, you will be making two types of measurements. Morphometrics are length-based measures of specific body parts, such as total length of the body or diameter of the eye. Although they can be compared to each other directly (for instance, the length of one fish versus another), this does not tell us much because fish change size as they age. However, when compared as ratios (for instance, head length/total length), morphometric measurements can tell us a lot. For instance, ‘cruisers’ and ‘accelerators’ might have small head-to-body ratios, whereas ‘maneuverers’ and especially benthic fish might have large ratios. At the end of lab, we will compile morphometric ratios for the different species examined in class. Your job will be to compare these ratios and see if you can tease out any patterns that can help determine life history traits. Meristics are counts of characters that occur more than once but are found in variable numbers between species (and sometimes within species). Because they are already dimensionless, meristic measurements can be compared directly. Interlude - Trip to the Fish Collection Before we begin our lab exercise, we will tour the UW Fish Collection, located in 005 FTR. We will look at the collection in general, and specifically at body types and how they relate to the life history of fish species. 1 Procedure - External Morphology You will work in groups of two to dissect a single fish. Identifying External Characters Use the provided diagrams as a guide to help identify the fins on your fish. Be careful not to rip the membranes between the fin rays, they are delicate. Draw your fish: label each fin, identify the caudal (tail) peduncle, the operculum (gill cover), and the lateral line. Include labels for each body part on your drawing (similar to Figure 1). Figure 1. Generalized fish showing external morphology. You will not see all these features in your fish - check with your TA if you are unsure of a feature. Body. Use a ruler or fish measuring board to make all morphometric measurements and record all measurements in millimeters (mm) so that ratios work properly. Using Figure 2 below as a guide, record the morphometric measurements listed in Table 1. Calculate the necessary morphometric ratios listed in Table 2. Make all morphometric measurements BEFORE the meristic measurements. Figure 2. Generalized fish showing external morphology along with morphometric measurements. Note that you do not need to measure all the measurements listed above, consult Table 1 for required measurements. 2 Fins. Take a closer look at the fins. Notice that some fins have hard, pin like projections (spines) whereas others are soft, segmented, and brush-like (rays). Occasionally, fins will have both spines and rays; however, spines are ALWAYS the most forward structures (closest to the head) on the fin. Carefully spread the fins, count the spines and rays, and record these meristic measurements in Table 3. Gill Arch. Gently pull back the operculum (gill cover) to reveal the gills. Most bony fish have four gill arches. The red material pointing towards the tail are the gill filaments (Figure 3). The spiny or nubby projections pointing towards the mouth are the gill rakers. The gill rakers will look very different depending on species/foraging type. Using your scissors, carefully cut the operculum back to expose the gills. Cut out a gill arch, leaving the others in place. Once the gill arch has been removed, gently rinse it off. Once rinsed, examine the gill arch to find the longest gill raker. Planktivorous fish use their gill rakers to strain plankton out of the water, whereas carnivorous fish do not. How do you think diet will affect gill raker type? Figure 3. Example of a gill arch. Internal Anatomy Once you have thoroughly examined the outside of your fish, it’s time to take a look at the inside. Fish harbor bacteria, which can cause serious infections. Wear Gloves and DON’T fool around. If you do cut yourself -even a little prick - TELL YOUR TA IMMEDIATELY. Start at the anus (a.k.a. vent). Using your scissors, cut along the belly of the fish towards the head. After your first or second snip, peel back the flesh to ensure you aren’t cutting into internal organs (remember that the anus is the end of the intestinal tract - you want to do several short snips and reposition your scissors so that you don’t cut the intestine. With flatfish, feel the side of the body to familiarize yourself with where the body cavity is. They have a modified body plan with all the organs located in a very small part of the body, close to the mouth. Gently press on the body until you have found where the body cavity lies. All other fish are much more ‘typical’ in that their body cavities run along most of the body length as in Figure 4. GO SLOW. It is difficult to glue a fish back together if you make a mistake. It is easy to make a slightly deeper cut if you haven’t cut far enough. Work your way through the pelvic fins (there are bones here!). Stop when you get to the base of the gill cover. Open your incision and gently move the internal organs such that you can now make two vertical cuts (up towards the dorsal fin), creating a flap of muscle/skin which you will lift to reveal the body cavity. MAKE SURE the tip of your scissors does NOT puncture internal organs - keep it pressed up against the cavity wall out of harm’s way. There may be bones which radiate down from the backbone and encircle the upper front portion of the body cavity. You will have to cut through these. Once you have opened the body cavity, you can carefully sort out the internal organs. Notice that they all lie together in a bundle. Connective tissue keeps them together. You will need to CAREFULLY cut this tissue to separate the major organs. The easiest place to start is back at the anus (end of the intestine). Remember that the digestive tract (gut) is a continuous tube connecting the mouth to the anus. You can literally follow this backwards. The intestine is pretty tough, so you can tug gently on it without breaking it. Once you have removed the connective tissues, you can stretch the gut out across your dissecting tray. Starting at the tip of the snout, measure the length of the gut and enter this in your Morphometric Table (Table 1). What do you think gut length means in terms of life history? 3 Figure 4. Generalized trout showing internal anatomy. Draw the internal anatomy of your fish. Try to identify the following internal organs and label them in your drawing (note the color, texture, and veining of each organ): • Intestine (connected to the stomach; well veined) • Stomach (connected to the intestine; closer to the mouth) • Liver (large, lobed organ towards the front of the body cavity; well veined. medium red in color) • Gonads (above the intestine near the back half of the body cavity; may not be present) • Fatty Tissue (intertwined in the mesenteries of the intestine; may not be present) • Heart (very dark red, associated with the gills) • Swimbladder (if intact, like a small balloon along the top of the body cavity; if broken, very hard to find) • Kidney (looks like a long, thin blood clot on the vertebral column) • Pyloric cacae (fingerlike projections that aid in digestion, near the front of the body cavity. You will see lots or none at all) • Gall Bladder (looks like a pea, found in the mesenteries of the upper intestine) • Spleen (looks like a very dark red fleshy bit found in the mesenteries of the upper intestine) Comparison Between Fish Look around the lab at the other dissections, comparing your fish with the others. How different is the arrangement, color and relative size of the internal organs? If time permits, open the entire intestine of the fish to speculate on its diet (it is highly recommended to do so!). Do any food items found reflect what you’ve learned about your fish? Comparison Between Bony and Cartilaginous Fish There will be a display of a dissected dogfish shark in the fume hood at the back of the lab room.