Dear Prof. Jean-Lou Justine,
I have used your method published with Briand Bray but have challenges with dilution ratio of sea water: tap water for slouching fish entrails and washing gills into bottles. The 1:3 ratio of sea water:tap water seem to still end up with high salt concentration because after each wash, the fish intestine hardens while gill tissues tear apart easily suggesting possible calcification of fish stomach and the intestinal lumen on one hand and erosion of gill epithelial cells and filament on the other to the detriment of parasite-in-view,
For marine fish specimens that are unavoidably frozen on-board fishing vessels before their purchase or laboratory custody, what is your experience as to the keeping-quality of parasites on the skin, GIT and gills before their parasitology and microscopy?
Secondly, while skimming off the supernatant upon slant -settling of the content of wash bottle one is worried at losing potential parasite with the debris being skimmed off. Can you suggest quick-win indicators of potential parasites apart from common debris when skimming the supernatant off?
Thanks for being a shining-light in this field. We all owe you some.
Dear Mohammad,
Answers to your various questions:
(1) The dilution of sea water.
The right dilution is one part of seawater and three parts of tap water; with a mean concentration of 36 grams of salt per litre of water, you will obtain a concentration of 9 grams per litre, i.e. 0.9% - the perfect solution to keep parasites alive for a while.
The hardening and calcification which you report have probably nothing to do with this.
(2) Frozen-thawed fish.
In this case, the parasites are dead. The method was designed for live parasites. Frozen-thawed parasites will generally give poor results with all methods. Frozen-thawed gill monogeneans should be manipulated with extra care because they are extremely fragile. The hot water step is useless in this case – the parasites are already dead and do not need to be relaxed.
(3) Potential loss of parasite with the debris being skimmed off. Parasites are generally denser than water and sink to the bottom: this is why the method works. A small proportion of parasites (if they are alive) might sometimes attach themselves to floating debris and might be lost. You might gently agitate the surface with a stick to be sure that they will detach from debris and sink.
Thank you for the compliment! We hope this method will be useful and very easy to everyone.
Article A quick and simple method, usable in the field, for collecti...
Dear Jean-Lou,
Thanks for your quick response and the paper attached which I read well before.
With the benefit of your response, parasite recovery from frozen fish samples are therefore nearly impossible.
How do you isolate and examine parasites from fish specimens obtained from commercial deep-sea fishing?
Dear Mohammad,
You can work on parasites from frozen-thawed fish! But the quality of the specimens will never be excellent for Platyhelminthes (monogeneans, cestodes, digeneans). It might be acceptable for parasitic crustaceans (isopods, copepods) and sometimes for nematodes.
For monogeneans, you can still collect specimens from frozen-thawed fish gills. The internal anatomy will be altered, but the sclerotised parts (haptor, copulatory organs) will be preserved.
I hope this helps,
Jean-Lou
I know people have had good results with liquid nitrogen freezing of bird intestines and later recovery of parasites. Has this been tried on fishes?
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