Prior to the fish dissection, it is important to review some background information on the internal and external body structures of anadromous fish. In this lesson, although we are studying salmon, my students dissect a trout. The internal and external body structures of the salmon are very similar to that of the trout.The trout is not an endangered species, so using trout for dissection purposes does not negatively impact our local stream environment. I get the fish for this dissection from our local fish hatchery.
I start the day's lesson by reviewing the expectations outlined in the science safety contract that each of my students signs at the beginning of the year. Since the students will be using sharp dissecting tools in the lab, it is very important that each student knows the safety and behavior rules of the lab.
After reviewing expectations, I display all of the dissection tools that students will use in the lab on the document camera. I name each tool and describe how it can be safely used. Each student group has a pair of scissors, spoons, hand lenses, gloves, and forceps.
Before I have students begin the dissection, I ask my students to review the external anatomy of the fish. To do so, I instruct students to put on their gloves and I deliver a fish to each student group. I remind students that the fish may be slippery, so they need to use care when handling their fish and keep their fish on their covered work space. I ask students to work with their science team to make observations about the external anatomy of the fish and to count the number of fins on the fish.
While students are working with their science teams, I visit each group of students and ask them questions to guide their observations. I use higher-level thinking questions to help students make inferences about the ways that the fish's external structures might impact their behavior or life in their naturl environment. Students frequently note that the fish's sharp teeth might mean that they have a varied diet or that the strong back fin might mean that the fish is a powerful swimmer.
After visiting each student group, I ask the student groups to share their observations with the whole class. I also ask each group to share the number of fins that their group counted on the salmon. Using the whiteboard, I draw a fish and label each fin. I take a few moments to review the signifigance of the adipose fin (fish with an adipose fin are wild as hatcheries remove the adipose fin for all released fish).
Before allowing students to begin their dissection work, I list the expectations for the dissection on the whiteboard. First, I want my students to use the salmon placemat to help them identify the internal organs of the fish. Second, I ask my students to remove each organ using their spoons and scissors and to record their work on the salmon checklist. Third, I ask the students to be prepared to share evidence with the class for their determination of each internal organ. I also tell my students that it is a special challenge to see if their group can remove the swim bladder without rupturing it.
I provide about 20 minutes of work time for students to collaborate with their science groups to meet the objectives listed on the board. During this time, I meet with each group and ask them to share their progress with me. When I see that students are on the wrong track with idenitfying internal organs, I remind them of the pictures on their placemats and the descriptions on their checklists. I encourage students to use these resources, along with their observation skills to make their determinations.
To conclude the day's lesson, I conduct a whole-group review. To do this, I display the students' work on the overhead projector. As I display the students' work, I ask students to work together to identify each organ that was removed from the fish and discuss with the students what each organ does in the fish's body. This review allows me to ensure that every student is successful at idenitfying internal anatomical structures and enables me to highlight the connection between the structure and function of internal organs. Using the document camera to diplay student work further aids the review process by giving me the chance to highlight successful student disssection work.