Fish in bags usually but not always die of hypoxia (lack of O2), even though the water is usually hyperoxic (supersaturated with O2). A fishes ventilation rate is a function of O2 in the water. The higher the O2 the lower the rate. Since the bag is hyperoxic the rate remains low and there is no adjust for internal chemistry problems, other than some dysfunction's of the Bohr and Root Effect, two physiological processes.
Bohr Effect; O2 bound up with hemoglobin which is released as needed.
Root Effect : The amount of O2 that can be stored or "banked" by respiration pigments at PaCO2 (Partial Pressure of arterial CO2)
As CO2 begins to build up in the bag and does not diffuse well through the bag there is an increase in the CO2
pressure gradient, between the bag and the fish. At some point, the CO2 in the bag begins to build
to the point where the fish has problems getting rid of his internal CO2. His blood begins to become
acid and adjustment are made to try and buffer the change in pH. In time this buffer effect fails
and you have acidosis. As this is taking place, oxygen pigments releases O2 . This releasing
continues and causes a shift in the Bohr effect (O2 combining curve,e.g.% hemoglobin O2 VS O2
partial pressure).This causes a decrease in the amount of O2 the pigments can hold a certain CO2
partial pressure (Root Effect). The fish is now hypercapnic. Some fish can increase their
ventilation rate in hypercapnic conditions and others can not. The O2 (pigments) often gets released
prematurely and can't store any in the pigments anymore, even though the water is hyperoxic...... he
dies from lack of O2 hypoxia, usually due to hypercapnic conditions.
There is a method to elevate this problem during shipping, with one draw back. The shipping method
is to use an organic/buffer TRISMA, which more or less cancels the nasties. The draw back is that
the buffer maintains the water at about a pH 8.2, which means any ammonia build up would be of the
more toxic form. However, after reading about all this a few years ago, I mentioned it to a large
marine fish distributor out of California and put him in contact with Patty Conway, a chemist at the
Sigma chemical corporation. Ted ordered some of the Trisma and had it sent to his overseas Pacific
suppliers (also his company) and was absolutely amazed at the results, in the reduction of shipping
moralities. He even went on to say that the fish required NO acclimation time, other than possible
temp.
Tris buffer is tris(hydroxymethyl)aminomethane. It's an inert organic
chemical with very powerful buffering capacity in the pH range fish need.
Sigma's trademarked name for it is Trizma. Sigma markets a product called
"Trizma, crystalline - fish grades", and suggest obtaining their Technical
Bulletin 106B which describes it. They offer pH 7.2 and 7.4 mixes for fresh
water fish, and a pH 8.3 mix for marine fish. I believe it is used in
concentrations of about 10 grams per gallon, and costs about 10 cents a
gram.
Sigma Chemical @ 800-325-3010.
Shipping fish with a drop or two of Methylene blue. MB is a light molecular organic/inorganic dye, that acts
somewhat similar to hemoglobin, in it ability to transport O2. The success of this can
easily be proven and I/we have done it many times, with keeping FW bait minnows over
night in containers. They are pretty much dead in the morning without it. There are also
some so-called modern "locked"/"target" buffers in the aquarium trade for 8.2, but they
still have a falling pH time, but using them is better than doing nothing with buffers,
especially with the addition of MB. And then there is MB antifungal, bacterial. parasite
properties/aides to the bagged fish. AND it ability to stop NO2 toxicity, although this
is a much greater problem in FW than SW
Some shippers also ship fish in Amquel, which also increases survival rates
In regards to acclimating the fish from a shipping bag, if the pH rises rapidly in the bag, there is the possibility that the H2CO3 in the blood is converted rapidly in large amounts to CO2. If that happened it would cause formation of CO2 bubbles in the blood and possibly death.
