Bagged fish – water quality changes.

Ever wondered what happens to the water quality of bagged fish? This is a question I ask my students when I teach them about water quality at Murdoch University.

Fish will continue to respire, consuming oxygen and producing carbon dioxide. They will continue to excrete ammonia as well. So what happens?

Dissolved oxygen will be diminished (and this is the reason why oxygen, rather than air, is used to inflate the bag for long journeys).

The carbon dioxide produced by the fish will and increase, and this will cause the water to become more acidic (think about the acidity of carbonated drinks like “Coke”). But this is not such a bad thing. Why? Read on…

Ammonia is excreted by the fish and will accumulate in the bag of water over time. It could rise to levels as high as 10ppm! But why don’t fish suffer from ammonia toxicity? Ammonia is more toxic when the water is more alkaline (it is the unionised form of ammonia that is toxic to fish – see extract from my recently published book: FishVetEssen_p46-47_Ammonia). But if we remember from the previous paragraph, the water pH declines due to the dissolved carbon dioxide and this is what keeps fish from dying. And this is why it us important not to open your bag of new fish while floating it in your aquarium when acclimatising the water temperature.

This is truly water chemistry in action!

A recent paper talks about such reactions but the scientists were concerned about decreasing pH when transporting marine fish. This is good and all, but I wonder if they take into consideration what effect the increasing ammonia levels would have on the fish if the water’s pH is not allowed to decrease.

Aquaculture
Volume 333, Number 7 (February 2012)
	Changes in pH during transport of juvenile cod Gadus morhuaL. and stabilisation using buffering agents
	Authors:	J.W. Treasurer
	Author Affiliations:	no affiliations available
	Source:	Aquaculture, Volume 333, Number 7 (February 2012)
	Page Numbers:	92 – 99
	Available Full Text:	Full Text: Subscription Required to view full text Format: PDF Size: Unknown Location: Publisher’s Site Authentication: Publisher’s Site
	Abstract:	Salmonids have been transported from hatchery to ongrowing units for many years, but little information is available on optimal conditions for the transport of marine finfish species. This study examined the changes in pH that occur under various simulated transport conditions of stocking density and fish size, and thereby recommends protocols for live marine fish transportation. The pH of the transport water declined rapidly due to the respiration of carbon dioxide. Various buffers (sodium bicarbonate, TRIS, Magnaspheres) were compared and maintained pH close to normal seawater levels. The decline in pH was greater with small (18g) rather than larger (32g) fish, at identical loading biomass in tanks, indicating that fish size should be considered when planning transport. Although unionised ammonia level increased with increasing stocking density (10 to 30kgm-3) the pH did not decline significantly. The use of air aeration as well as oxygenation reduced CO2levels indicating that aeration stripped the CO2from the water. Non invasive measurements of free cortisol release into the tank water by juvenile cod indicated primary stress response to handling events. This study demonstrates that cod juveniles will be exposed to fluctuating pH in transport tanks, and buffering of the pH and stripping of CO2by aeration to reduce fluctuations is recommended.
	Citation:	J.W. Treasurer . Changes in pH during transport of juvenile cod Gadus morhuaL. and stabilisation using buffering agents. Aquaculture, Volume 333, Number 7 (February 2012), pp. 92-99,
	URL:	http://ejournals.ebsco.com/direct.asp?ArticleID=4722AD404EF8FCC51D3A

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