Perch -- our first real vertebrate!

This week was a nice change from previous weeks in that it was not nearly so rushed because we only had one dissection.  Also, this week the animal was large enough that we could really identify the organs without the magnifying glasses, so that was nice!!

We looked at perch, which have bilateral symmetry like all other vertebrates (I think).  They have eight fins total, which we could all see: two on their backs (dorsal), two pectoral, two pelvic, one caudal, and one anal.  Perch have nostrils that are of course not for breathing but for smelling things in the water like prey, predators, and pollution.  They don't have eyelids, we assume because they don't need them.

They have a complete digestive system, which is pretty similar to ours; food goes in the mouth and then through the esophagus (which was so short we couldn't really see it), then to the stomach.  The liver, gall bladder, and pancreas all help with the digestive process, and there is a large intestine and finally the anus.  We discussed the functions of the pancreas a bit, one of which is to respond to increased blood sugar by releasing insulin.  Insulin allows the sugar to leave the blood and go into the muscles and tissues.  When the pancreas is not able to regulate blood sugar, the result is diabetes.  Type 1 diabetes is when the immune system attacks the insulin-producing cells, and type 2 diabetes is when the pancreas doesn't make enough insulin or the body doesn't respond to insulin but the insulin-producing cells have not been destroyed.

We saw the gills and also these things called gill rakers, which keep large food particles from getting into the gills.  They looked pretty much like this:

The opercula are the hard things that cover the gills and protect them.  The circulatory system is the first closed circulatory system we've seen.  There is a small two chambered heart that pumps blood first to the gills to get oxygen and then to brain and rest of the body to give the cells and tissues the oxygen they need.  Then, the blood comes back to the heart.  It is a low pressure, single circuit system that has both veins and arteries.  The crayfish had a heart and some arteries, but then the blood flowed freely through the animal's body, so it was an open circulatory system.

One special thing about the perch is that it has something called a lateral line on each side.  It really looks like a little line on each side of the fish's body and it has hair cells for detecting vibrations in the water.  When we say "hair cell" we don't mean hairs, but little cells that have a part sticking out of them that looks like a hair.  When the hair-like part is moved, it sends information to the fish's brain about the vibration it detected.  This is something cool about fish that we don't have, although our ears use similar methods for detecting sounds and keeping us balanced.

The pictures in our dissection guides mentioned two brain parts, the cerebrum and the cerebellum.  We forgot to go through the details of the perch nervous system, so we'll talk about that next time.  Three things I thought were cool about the dissection:

1. The swim bladders were HUGE!
2. The liver was easy to identify and looked like other animals' livers.
3. The heart was really close to the head and mouth, but we could take it out and examine it.

Lastly, we discussed current scientific research on perch.  Since several students focused their blog posts on the topic of eating perch, I chose this article, which looked at food contamination issues.  Basically, the researchers bought various fish from markets in Saudi Arabia and put them on ice for 0, 24, or 48 hours, and then fried some of the fish.  They measured the levels of chemicals called "biogenic amines" in all the different types of samples and compared them.  These chemicals are made by bacteria that live in the fish and are the major cause of food poisoning from fish.  Symptoms include hypertension (high blood pressure), headaches, diarrhea, rash, and can result in death on rare occasions.  They found that the levels of these chemicals increased the longer the fish were stored, and frying the fish increased the levels further.  So be careful of your fish fry!  Here is some fried perch -->