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Outreach: Fish are What They Eat: Trophic Morphology for Kinder


IGERT PIs Postlethwait and Cresko taught two-day session at the Water Wonders Summer Camp at the Science Factory to kindergarten through second grade students. The goal of the course was to introduce early elementary school kids to the concepts of unity of type (that related groups of animals share similarities in morphology including sharing the same bones), and variety in form (that although different groups of animals share the same bones, the shapes and sizes of these bones differ to produce different morphologies), and that variety in form adapts species to their environments.

To demonstrate these concepts we focused on variation in mouth morphologies among fish populations and how morphologies are adapted to different foods that animals eat. Specifically, we focused on suction and ram feeding strategies that different fish species or populations use to obtain prey. To convey ideas of differences in mouth morphology, we utilized a number of hands-on activities followed by oral explanation — most of it coming from the kids as prompts — as well as videos and powerpoint presentations.

On the first day students watched feeding videos of two closely related damsel fish, one demonstrating suction feeding and the other ram feeding. To further express this message, we had the students use only their mouths (no hands) to eat M&M candies either by picking them up with their mouths, ram feeding, or by carefully sucking them in, suction feeding. We had them note how they held their mouths for these different activities. We then presented students with different types of vertebrate skulls and asked students to try to determine what animal the skull belonged to and also what types of food it may eat by observing the shapes of the mouth and teeth. We followed by looking at the stickleback facial skeleton in a fixed and stained preparation from a ram feeding population. We compared it to a similar preparation from a suction feeding population of threespine stickleback, and finally a fixed and bone stained suction feeder, the Gulf Pipefish. At the end of the first day, students set minnow traps in the Discovery Ponds in front of the Science Factory, which are connected to the Willamette River by a small slough. Students helped think about the best places to put traps in the ponds to increase the chances of collecting stickleback.

On the second day, students created models of fish mouth bone morphology using colored thin cardboard and brass brads to serve as joints. The models demonstrated how these bones are connected and move together to open or close the mouth. Students were told that muscles can only pull things, they can’t push, and so students had to figure out where muscle attachments are located by seeing what actions are necessary to make the model open and then close its mouth. Using the model, students changed the length of one of the bones by swapping out one bone for a longer one. This model then showed them what has to happen in terms of skeletal morphology to make the mouth open faster and hence change a ram feeder into a suction feeder. To further get an idea of the difference in suction and ram feeding, children tried to catch sea monkeys (artemia, small crustaceans) using different length plastic pipettes. Two lengths of pipettes were used one long to demonstrate suction feeders and the other short and wide so that suction was reduced to a minimum, to demonstrate ram feeding.

Students took home worksheets overnight that had diagrams of different types of fishes emphasizing skull shape. They had to talk with their parents and imagine, draw, and color different types of food each of the fish might eat and whether the fish was likely a suction feeder or a ram feeder using the lessons that they had learned from the demonstrations and activities.

We went out to the Discovery Ponds to see what had swum in overnight. Students were amazed to find 20 or more stickleback in most of the traps. We brought these wild fish into the classroom, placed them in an aquarium, and fed them sea monkeys. Students had to determine whether the local fresh water stickleback were ram feeders or suction feeders by observing their feeding behavior, which was ravenous. We brought from the lab live suction feeders, Gulf Pipefish, to allow students to see first hand the differences in ram and suction feeding. Again, it was remarkable that students so young would already know so much about the natural world and would be so adept at drawing conclusions from making their own observations. Photographs of the stickleback behavior sessions and the stickleback trophic morphology sessions are available at our website,

Address Goals

This helps to introduce grade school children to the discovery of science. In it we reached minority children with otherwise little access to this type of training.