Basic Methods for the Study of Reproductive Ecology of Fish in Aquaria

The overall goal of this procedure is to implant identifying tags in live fish without injury, to facilitate various ecological studies using wild caught fish in aquarium. This method can help answer key question in the fish behavioral ecology field;such as the reproductive and social behavior of fishes. The main advantage of this technique is that we can conduct experiment on the fish without any major negative effect on their behavior.

This section shows how fish are implanted with VIE tags. If the fish cannot be held by hand because it is too small, build a surgical table to hold such fish. First cut a soft sponge into a five square centimeter section, 20 to 25 millimeters tall.

Then cut a groove into the sponge that is five to 10 millimeters deep and is as wide as the fish it will hold. Next cut a piece of 0.3 millimeter thick polyvinyl chloride to precisely fit over the sponge. Then add a valley fold to the PVC, and position it into the central groove.

Now transfer the assembly to a 160 millimeter dish with 30 millimeter walls, and fill the dish with water from the recovery tank until the PVC board is completely immersed. This completes the surgical table. Now proceed with tagging a fish.

To begin, choose an injection site and tag color. It is safer to inject the thick muscular dorsal or caudal regions, then to inject the abdomen where internal organs may be pierced. If the study species is large enough there will be eight reasonable positions for a tag.

With just one tag color and use of all eight positions, 154 unique identifying patterns can be made. For the tag color, choose the one that will best contrast the body color. Then prepare the VIE tags using the tagging kit.

Mix the elastomer materials and load it into a three millimeter syringe with a 29 gauge needle. Next prepare two water tanks to use during the tag injections. One for anesthesia and one for recovery.

Use an air stone to mildly circulate the water in the recovery tank. For the anesthesia tank, make a one to one mixture stock of two methylquinoline and 99.5%ethanol. Make just enough to have an 18 ppm of two methylquinoline in the tank, and mix it thoroughly into the tank water.

After completing these preparations, proceed with tagging the fish. Transfer an individual fish to the anesthesia tank and cover the tank so it cannot escape. Fine tune this step according to the species.

The concentration of anesthetic is an important factor. Wait until the fish does not react to water vibrations or to being touched. Do not wait for the operculum to stop moving or the fish will be at a high risk of death.

When the fish is ready, remove it by hand. Use a cold water acclimated hand so the fish is not warmed too much, keeping it stronger. Lift a fish from the anesthesia tank and quickly take physical measurements.

If a fish appears to recover during this time, immediately transfer it back to the anesthesia tank. If the fish is small, transfer it to the surgical table ventral side down in the PVC groove. If the fish is very small, use a binocular microscope to make the injection.

If the fish happens to be large enough to hold by hand, inject it handheld. Now position the beveled side of the needle outwards, and the pointed side toward the fish. Then insert the needle subcutaneously more or less parallel to the body and very shallow, just under the skin.

Ultimately the goal is to make the tag visibile, so adjust as needed. Next, inject the VIE tag while withdrawing the needle and stop the injection before the needle bevel reaches the entry point. Injecting a relatively wide area on the fish makes it easier to judge the stopping point.

If the injection doesn't go well, make certain that the anesthesia is working and that the needle is quickly inserted to the appropriate depth. Once injected immediately transfer the fish to the recovery tank. If recovery takes more than two minutes, gently circulate the water by hand.

After the fish recovers, return it to the rearing aquarium using a net. In the rearing aquarium, provide 10 ppm of Elbagin for three days to prevent wound infection. If the fish are housed under low visibility conditions, the VIE tags can be seen more clearly using UVA filtered light.

Reproductive ecology of Trimma marinae, the Princess Pygmy Goby, was studied using VIE tags. Wild individuals collected offshore of Amami Oshima, Kagoshima Prefecture, Japan, once per year. Most survived and spawned about seven days after capture.

The VIE tags were visibile and allowed identification of individual Gobys even though they are quite small. The Pygmy Goby tended to establish reproductive pairs between which most of the observed spawning occurred. Only males were observed caring for eggs.

Aggressive interactions between the females suggest that the monogamous mating system may result mainly from mate guarding. When eggs were deposited on a waterproof sheet they were visible enough to be counted. After the sheet was removed, photographed and returned to its former place in the aquarium, the nesting male immediately continued paternal care.

Analysis of the egg counts revealed a positive correlation between female fecundity and female body size. Whereas no difference in reproductive success was observed among differently sized males. Since developing this procedure, we have been able to perform various behavioral experiment using a lot of variety of fish more easily and accurately then we had using other fish identifying systems.