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Author Topic: Fishy forensics: Could a hook rust while inside a fish?  (Read 1887 times)

Offline SquarishTriangle

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Some of you might remember me. I haven't been on here in a long long time!

Multidisciplinary question for you all. A bit of general chemistry, a bit of physiology, a bit of biochemistry, and a bit of fishy forensics. I dabble a little in all of the above, but not enough to piece it all together.

Background:
- I saw a fish today as a patient. A fiddler ray, in fact. It was a very sick fish, so unfortunately it had to be euthanised and undergo a post-mortem examination.
- Although, not the main reason it was so sick, this ray was found to have a fish hook basically floating freely within her coelome (the main body cavity). It was a very rusty hook.
- We know for certain that she has had no exposure to fish hooks in the last 8 years, since she lives in captivity. However, prior to 8 years ago, she lived in the wild, so probably encountered the fish hook there.
- Given that the hook was not in the digestive tract, and there was no other point of entry found, we assume that it once entered the mouth, then the digestive tract, then perforated the stomach/intestine and made its way into the coelome, but (amazingly) healed up and did not die in the process.

Question:
- Could a brand new fish hook rust inside either the a) the digestive tract or b) the internal body cavity of an animal? Are the necessary conditions for metal corrosion available within an animal (ie. oxygen, acidity etc.)?
- Alternatively, did the hook need to have rusted BEFORE it was ingested (eg. sitting on the seafloor, attached to another fish etc.)?

Any brainpower would be greatly appreciated!

« Last Edit: 17/03/2016 10:15:30 by SquarishTriangle »


 

Offline chiralSPO

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Re: Fishy forensics: Could a hook rust while inside a fish?
« Reply #1 on: 17/03/2016 13:12:12 »
I would guess that a hook could rust inside a fish. The process might be significantly slower than for a hook in the open water, due to the availability of oxygen, but within 8 years, I would not be surprised at all.
 

Offline chris

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Re: Fishy forensics: Could a hook rust while inside a fish?
« Reply #2 on: 17/03/2016 18:51:28 »
Some of you might remember me

Wow - great to see you back! I was thinking of your and your animal contributions the other day when I was dealing with a zoological question... hope you can stick around?

Anyway, regarding your question, I think your suggestion that the hook penetrated via the GI tract is a good hypothesis. There are similar examples of foreign bodies working their way through multiple viscera in humans, most notably IUDs (coils) which have been known to perforate the uterus and end up in the peritoneal space.

Slightly surprising that there wasn't a huge mass of adhesions around the hook... or was there?

To address the rusting issue, iron does oxidise in the body and I suspect it can form iron oxide at physiological pH (7.4) - maybe Bored Chemist can chip in here?
« Last Edit: 17/03/2016 20:48:44 by chris »
 

Offline SquarishTriangle

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Re: Fishy forensics: Could a hook rust while inside a fish?
« Reply #3 on: 18/03/2016 00:43:58 »
Thanks ChiralSPO and Chris!

Amazingly, there wasn't any evidence of adhesions or inflammation visible to the naked eye. If fact, there was no obvious evidence of an entry point. The hook was just sitting there, beautifully, on the surface of the liver, loosely attached to the capsule.

Certainly in other animals, there should have been a huge inflammatory reaction, adhesions and peritonitis associated with a GI perforation. Cattle are famous for this, in the form of "hardware disease" (traumatic reticuloperitonitis and reticulopericarditis). But cows are tough, and they don't always appear sick. A dog or cat would get a horrible peritonitis and potentially die within the first few days. Birds are similar. I have no idea what a chondrichthyan fish is supposed to do.

Chris - I endeavor to pop in more regularly. Life as a grown-up scientist is certainly hectic. Currently approaching the end of my residency and my second Masters. Then I'll be free!
 

Offline Bored chemist

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Re: Fishy forensics: Could a hook rust while inside a fish?
« Reply #4 on: 24/03/2016 14:39:44 »
AFAIK all animal cells need oxygen, so anywhere in a fish (with the possible exception of the gut contents) there will be oxygen
And the pH is roughly the same as sea water and iron rusts well in that- as long as there is oxygen.
So rusting within the fish is perfectly reasonable. Though, of course, it might have been rusty before it met the fish
 
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Offline SquarishTriangle

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Re: Fishy forensics: Could a hook rust while inside a fish?
« Reply #5 on: 25/03/2016 05:04:12 »
Thanks, Bored Chemist.

To be honest, I was hoping the answer would be "no". But I'm happy to be wrong.
 

Offline chris

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Re: Fishy forensics: Could a hook rust while inside a fish?
« Reply #6 on: 25/04/2016 08:15:31 »
My insight into this answer is from the training I had in opthalmology as a medical student. A sizeable proportion of the presentations to the eye clinic for penetrating injuries were patients with iron slivers in their eyes usually as a consequence of grinding metal or, more often, hitting a chisel with a hammer. Left in situ, these particles can "rust" inside the eye. Iron salts are retinotoxic, leading to longer term secondary sight loss over and above any consequences of the direct initial injury. It was on this basis that I suspect that an iron hook would rust, but I am reassured by the input of boredchemist - thanks!
 

Offline SquarishTriangle

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Re: Fishy forensics: Could a hook rust while inside a fish?
« Reply #7 on: 28/04/2016 11:47:24 »
Wait, humans would actually leave bits of metal in their eyeballs long enough for rust to form??
 

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Re: Fishy forensics: Could a hook rust while inside a fish?
« Reply #7 on: 28/04/2016 11:47:24 »

 

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