Once fish are sealed in the bags and boxes, they must have everything needed to survive until they reach their final destination, which can be days later. The key to success is to protect fish against the deteriorating conditions.
Some practices, like adding pure oxygen gas to the bags, are based on sound science and reason; others, like adding antibiotics to the water, may do more harm than good. Seek the advice of experienced shippers or a local Extension specialist when considering shipping practices you are unfamiliar with.
Oxygen:
Fish need oxygen to survive and oxygen is actually hard to dissolve in water. During shipping, it is easy for the fish to consume more oxygen than is being replenished by diffusion unless you use a concentrated source and provide enough to last for the duration of the shipment.
The bag should contain no less than half its total volume in oxygen, and many shippers seal their bags with at least two-thirds oxygen. Compressed cylinders of oxygen can be rented or purchased from commercial sources.
A regulator controls the flow of oxygen out of the cylinder and through a hose and valve to fill the individual bags. A standard “trigger” valve is the most commonly used, but for operations with a large daily volume a foot-operated valve may be more ergonomic.
Heat/cold packs:
Temperature must be controlled during shipment, especially during extreme weather conditions or if the shipment will have a long layover at an airport where the boxes may be exposed to the weather for a considerable time. The use of insulated boxes may not be enough.
Chemical packs, which are available for both heat and cold, usually require the user to mix the ingredients within a pouch. Depending on the type used, these packs can last no more than 8 hours or as long as 100 hours.
Some heat packs use potassium compounds that give off heat when exposed to oxygen. In a sealed box, these packs often stop working once the oxygen in the box is exhausted, so they may not last as long as the labels claim.
The type, size and number of these packs to use depends on the size of the box, the duration of the shipment, and the conditions of the “weather” during shipment. The shipper should be careful not to use too many. Reusable ice packs that can be refrozen repeatedly are also used.
Whichever type is used, packs should be added to the box just before it is closed and sealed. Avoid putting the packs on the bottom of the box as the water will be directly affected (heated or cooled) if the bag sits directly on the heat/cold pack.
Some shippers tape the packs to the underside of the lid, and others wrap them in newspaper to prevent direct contact with the water through the plastic bags.
Tranquilizers/sedatives:
Use of chemical tranquilizers during shipment is sometimes warranted, especially for large species. Tranquilizers slow respiration and metabolism, thus decreasing the rate at which water quality deteriorates.
Tranquilizers also prevent some physical damage to the fish and shipping container. In the United States only two chemicals are legally available for tranquilizing/sedating fish. Metomodate, sold as Aquacalm is allowed only for ornamental and aquarium species.
This product was just recently made legal through the drug indexing section of the Minor Use for Minor Species Act (MUMS). Dosage ranges from 1 to 10 mg/L, depending on the species and duration of the treatment.
MS222, or Tricaine is also approved for use with finfish during transport, but is typically used for short periods. Dosage ranges from 5 mg/L to 50 mg/L, depending on the species and duration of the shipment.
There is some species data for both Metomodate and MS222. Be very careful when using these products with species for which there is no data. Before using these or any other products, read the entire label and seek the advice of an aquaculture Extension specialist if you are still unsure.
pH Buffers:
During shipment, carbon dioxide levels increase in the bags, which causes a drop in pH. The extent of this drop in pH depends on the amount of carbon dioxide produced and the buffering capacity of the water.
The buffering capacity of water is often described by the term “alkalinity,” which is a measure of the water’s ability to neutralize acids. If shipping water has low alkalinity, dissolved carbon dioxide can cause significant drops in the pH, so buffering agents may need to be added.
The most common buffers for adding alkalinity contain the weak bases bicarbonate (from sodium bicarbonate, also called baking soda) or carbonate (from calcium carbonate, also called limestone). Either of these can safely be added to shipping water.
While small buffering packs can be added to each bag, it is less expensive and more effective to treat the water before shipment. Water for shipping fish should have a total alkalinity of at least 100 mg/L expressed as an equivalent of calcium carbonate.
Non-carbonate buffers are also available to increase the water’s acid neutralizing capacity. The most common is called “tris” or “THAM,” which are short names for tris(hydroxymethyl)aminomethane.
Tris is an organic compound that buffers water at a pH of 7 to 8.5. It can be used at 2 to 4 g/L and can be purchased in prepackaged buffer packs to add directly to the water in the bags. Tris is best used when a large number of fish need to be shipped in a small volume of water and excess carbon dioxide is a concern. It will interfere with the effectiveness of some ammonia removal products.
Zeolite:
Zeolites are common clay-like minerals that can adsorb positively charged ions (cations) from water. One type of zeolite, clinoptilolite, has a unique crystalline structure that adsorbs ammonium ions.
Zeolite is much more effective in removing ammonium ions from freshwater than from seawater, as other cations in the seawater compete with the ammonium ion for adsorption. Zeolite specifically selected for aquaculture purposes is available from several sources. Zeolite should be used at a rate of 15 to 20 grams/L (57 to75 grams/gallon) in shipping water.
It should be thoroughly rinsed with freshwater before use; otherwise it will make the water in the bag turbid or cloudy. Most shippers put it in small mesh bags so it will not be loose in the bottom of the fish bag. This makes it much more convenient at the receiving end of the shipment, as the recipient does not have to separate the loose granules from the water.
Ammonia removal:
There are several products that claim to chemically bind with, or “remove,” ammonia from water. Some do not list their active ingredients, even on the required Material Safety Data Sheets (MSDS), so it is impossible to make any kind of recommendation on their use or effcacy. Active ingredients that are listed on other products, their effcacy, and their effect on shipping water, are as follows:
Sodium hydroxymethanesulfonate. In water, the sodium separates from this molecule, allowing the active ingredient hydroxymethanesulfonate to bind with ammonia in the water. The resulting by-products are water and sodium. This reaction takes place over a wide pH range but works best when pH is above 7.0 as there is more ammonia present in the non-ionized form.
Hydrosulfite and sodium bisulfate. The sulfite/sulfate portion of these molecules can bind with ammonia in water and reduce its toxicity. However, they also behave as acids in water and can lower the pH significantly.
Aliphatic amine salts. This is a large group of chemicals so it is diffcult to make recommendations on their use, effcacy, or effect on other water quality parameters. None of the commercial products reviewed for this publication listed the specific amine salts used.
Salts:
Osmoregulation is the continuous process by which fish maintain a balance between the salts inside their bodies and the salts in the surrounding water. In freshwater fish there is a higher concentration of salts in the body fluids than in the surrounding water.
The body fluids of saltwater fish are more dilute than the surrounding water. Osmoregulation is an energy-consuming process in fish and when the balance is disturbed, fish will be stressed. Fish are handled a lot as they are counted, sorted and moved from one place to another with nets, buckets, bags, etc.
This handling can damage the slime coat, skin and other external barriers that are needed to maintain the osmoregulatory balance between inside and outside conditions. Damage to this barrier can lead to further stress during shipment.
Reducing the difference between internal and external concentrations of salts can reduce the energy expended in osmoregulation and reduce stress. Adding salt to the shipping water for freshwater fish relieves some of the osmoregulatory stress.
Likewise, lowering the salinity of shipping water for marine fish will create a closer balance between the inside and outside concentration of salts. A difference as small as 0.5 to 3.0 parts per thousand will help during shipping. For freshwater shipments, use 2 to 11 grams/L (7 to 43 grams/gallon) of simple, coarse salt (i.e., sodium chloride, “rock salt”).
Salts treated with anti-caking agents, such a nitroprusside, should not be used because there is evidence that they may be toxic to some fish. Other salts, especially calcium chloride (used primarily to melt snow and ice), have additives that accelerate their melting and should also be avoided. Salt for human consumption often contains iodine and cannot be used with fish, as it is extremely toxic.
Some species of fish show no apparent problems if the salinity is changed quickly by as much as 3 ppt, so salt is often added directly to the shipping water. However, some experts recommend slowly acclimatizing all fish to changes in salinity over a period of several days before shipping, and then again at the receiving end.
Antibiotics:
Antibiotics should not be used in shipping water. Not only is this a non-labeled use, but there is also little evidence to support any benefits. The short-term use of antibiotics in fish can cause some bacterial strains to become resistant to antibiotics, and it is rare that the treatment will be continued for the required length of time after the fish reach their destination. If a bacterial disease is suspected, fish should be treated before shipment (see the following section on prophylaxis) or not shipped at all.
“Bacteriostatic Agents”
Some chemicals have been used historically in aquaculture as “bacteriostatic agents” to interfere with or even stop bacterial survival and reproduction in water. The most common of these associated with shipping fish are acriflavin and methylene blue. Neither of these products is labeled for aquaculture or for use in fish shipping water, and there is little to support their use in the literature.
Authors:
Craig Watson, Kathy Heym Kilgore and Carlos Martinez
