Are crappies resistant to parasites?

A few years ago I went ice fishing and caught some bluegill and crappies. At the time I found some yellow grub type parasites in the bluegills. I posted a few pictures and short video here: http://forum.nanfa.o...gill +parasites Although I had caught more crappie than bluegill, I noticed that none of the crappies had any visible parasites. I thought that seemed a bit odd but could easily just be coincidence. Well nearly 4 years and many fishing trips have since gone by and I have yet to find parasites in a crappie.
Since the 2 trips mentioned in the linked post, I have made several ice fishing trips to the same lake over the past 3 winters and another one this winter just a few days ago. On all of those trips however I have only caught crappies, so can't really compare their lack of parasites to anything other than the bluegills from 4 years ago. On the other hand, in June of 2010 my wife and I went to our family's lake cabin in northern Minnesota and caught several sunfish which we kept. Mostly bluegill, but also a pumpkinseed and rockbass. We wound up throwing them all away, as upon cleaning them found the flesh from every fish was filled with the yellow grubs and peppered throughout with black spots. On a July trip to the cabin, we caught 4 or 5 crappies and several small perch. We didn't keep any perch but a brief examination revealed they were all covered with black spot. They also had yellow grubs in the fins and around the gill areas visible just beneath the skin. I was reluctant to keep the crappies but also curious as to what I would find upon cleaning them. Was quite relieved to find them clean when I filleted them. In 2011 two more trips to the cabin basically resulted in a repeat of the crappie/perch experience.
After all of that, it is seeming less likely to be coincidence. So I am now wondering what keeps the crappies free of parasites? Is it their life history? Is there something that perch, rockbass, bluegill, and pumpkinseeds do that exposes them to parasites that crappies just don't do? Do crappie have a physiological resistance, or am I completely wrong and it is just a coincidence? Has anyone caught crappies that have had parasites particularly the yellow grub or black spot?

I do not think they are resistant, rather the free-living stages may not be uniformly distributed in the water column in time or space. The differing species of sunfishes are also not always uniformly distributed or in a pattern that overlaps the parasites free-swimming stage. Fish and free-swimming stage must meet up for infection to occur. In my production ponds I strongly suspect many but not all of the bluegill have home ranges and wind driven currents may concentrate the free-living stage of the parasite causing a given fish to have risk of exposure that is related to where the parasite concentrates and the fish's home range.

Additionally, black and white crappie both get yellow grub when in shallow ponds loaded with ramshorn snails Heliosoma sp.

Yellow grub and blackspot flukes cannot infect humans -- It's OK to keep and eat those fish. Maybe the locations where bluegills feed (more benthic) vs where crappie feed (more mid-water) affects their exposure to fluke larvae. Bluegill also consume more snails than do crappie.

We didn't keep any perch but a brief examination revealed they were all covered with black spot. They also had yellow grubs in the fins and around the gill areas visible just beneath the skin. I was reluctant to keep the crappies but also curious as to what I would find upon cleaning them. Was quite relieved to find them clean when I filleted them.

Yellow grub and blackspot flukes cannot infect humans -- It's OK to keep and eat those fish.

Are there any fish parasites that can infect humans?
I'm just thinking about how raw cow/pig/chicken = can't be safely eaten but raw fish = sushi.

Edited by EricaWieser, 08 January 2013 - 06:27 PM.

Some marine fishes can pose a risk.
Consumption of some of native crayfishes raw can be very risky.

YES: tapeworms, nematodes, lung fluke, liver fluke ...
There are generally more in tropical countries, but we do have some in N.Amer.

http://suite101.com/...aw-fish-a138279

Yellow grub and blackspot flukes cannot infect humans -- It's OK to keep and eat those fish. Maybe the locations where bluegills feed (more benthic) vs where crappie feed (more mid-water) affects their exposure to fluke larvae. Bluegill also consume more snails than do crappie.

I know I could have eaten them safely, it's just the grossness factor of knowing I'm eating worms. I usually don't let that bother me if there are just a few and I can cut them out, but the sunfish we threw away were packed with them, and the perch were released as they were just too small to keep parasites or not.

YES: tapeworms, nematodes, lung fluke, liver fluke ...
There are generally more in tropical countries, but we do have some in N.Amer.

http://suite101.com/...aw-fish-a138279

Before that post, I ate raw fish. Since reading that hyperlink, I think I'm done. Lung worms? Aughkc.