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Fish species in experiments with DSTs

The first tagging experiment on fish with Star-Oddi's tags was performed in Icelandic waters in 1993 on Atlantic salmon (Salmo salar L.). In addition, the tags have been used in Icelandic waters on Atlantic sea trout (Salmo trutta L.), Atlantic cod (Gadus morhua) and on Baltic salmon (Salmo salar L.) since 1995 and Arctic charr (Salvelinus alpinus) since 1997. Using the smallest DST enables researchers to tag fish that are about 20 cm in length. In the salmon experiments the aim was to study the homing migration pattern in coastal waters and the sea migration (feeding) pattern of sea trout.
Star-Oddi's DST's have been used on Cod¹ (Gadus morhua), Saithe (Pollachius virens), Anglerfish (Lophius piscatorius L), Plaice (Pleuronectes platessa L) and some Ocean read fish species (Sebastes mentella).

Preparations
Depending on the country various legislations may apply to tagging experiments, theCATAG report² gives overview of tags, tagging, relevant legislation and fish welfare issues. The US Animal Welfare information Center also has some information regarding tagging. Anesthesia is frequently used and is compulsory in some countries when surgery or intrusive methods are used for applying electronic tags, it is often needed to reduce or stop movements of fish during handling. Some avoid using anesthesia as it might not be necessary or in some cases detrimental, in such cases other measures are used to try to minimise the effect of capture, tagging and release.

External Tagging (Salmonids)
After the fish has been anesthetised (e.g. 0.1% MS-222) it is placed in a special box with support on both sides (drawing available from Star Oddi). The fish is kept submerged in low concentration anesthetic solution (e.g. 0.05% MS-222). Two needles are pushed through the dorsum of the fish close to or in front of the dorsal fin. The spacing between the needles should match the length of the tag. The attachment wire of the tag (steel threading-0.5 or 0.6 mm) is threaded through each needle and fastened on the other side of the fish. Where the steel threading comes in contact with the fish, it is placed in a plastic tube to prevent erosion of the flesh by the attachment wire. After the surgery the fish are allowed to recover in water that has no anesthesia and then released.

Internal tagging
If anesthetics is used, the application is more or less the same as for external tagging. After the fish has been placed unders anesthesia it is placed on its dorsum in a V shaped surgical saddle and operated on. At the Marine Research Institute in Reykjavik, Iceland a method has been developed for surgical application of DST's to Atlantic cod where no anesthesia is used. This method has been accepted by the Icelandic committee for treatment of experimental animals. Experience has shown that if cod is placed and stabilised dorsal side down, as in the V shaped tagging-saddle, there is very little movement and no reaction to the surery. After the surgery the cod can be released directly into the sea or kept for surveilance. The time the fish has to be kept onboard the tagging vessel is greatly reduced. During the surgery, oxygenated water is directed through the mouth and over the gills, the eyes of the fish are covered and kept moist with a pre-soaked towel. An incision is made 3 cm from the mid-ventral line and anterior to the pelvic fins. A needle is inserted through the body wall close to the incision, and the plastic identification tube from the tag is then threaded using the hollow needle to the outside. The tag is inserted into the body cavity and the incision is closed with sutures.

More detailed information can be obtained from Star-Oddi concerning both of these methods. For long time measurements, internal tagging is recommended. There have been almost no reports of tag loss from the fish or of wounds related to internal tags. External tags can "grow" out of the fish. How fast the tag will grow out of the fish is dependent on the growth rate of the fish, this means that even if the fish is never captured it will, eventually, get rid of the tag.  

Recapture of the DST electronic tags is considerable higher than that of conventional ones. There are probably two reasons for this. The first one is that the DST's are very easy to spot on the fish and look "advanced". The second reason is, that in most cases a reward is issued for the return of the tags. 

Plaice (Pleuronectes platessa)

The flatfish species plaice was tagged with the Icelandic data storage tags for the first time in April 1998 in Breidafjordur, on the west coast of Iceland. Breidafjordur is one of the spawning grounds for plaice in Iceland. This is the first time a flatfish was tagged with our tags (DST 300), parts of the tagging technique had to be changed to adapt for use on flatfish. The experiment was carried out by fisheries scientists from the Marine Research Institute in Iceland, the second phase of the tagging experiment was carried out in August 1998.    

1 Palsson &Thorsteinsson 2003, Thorsteinsson  1995, Thorsteinsson and Marteinsdottir 1998
2 Thorsteinsson 2002