BAR TODAY || Official Quarterly Publication of the Bureau of Agricultural Research

Saving the blue tang
by Rita T. de la Cruz

January-March 2004
Volume 6 No. 1

Blue tang (Paracanthurus hecatus)

The blue tang (Paracanthurus hepatus) grows one foot long while in the wild and half of that size in captivity; has erectable razor sharp spines at the base of its body in front of its tailfin; it has an oval, compressed body and is blue, thus the name.

Blue tang is a high-priced marine aquarium fish in the Philippines. It belongs to the family acanthuridae that consists of 72 species of sturgeon fishes, lancet fishes and tangs. Like any acanthurids, the blue tang inhabits the rocky or coral reef areas and mainly feeds on zooplankton. Its population is distributed throughout the South China Sea and from the Indo-West Pacific to East Africa.

Its beautiful and contrasting color makes it a favorite fish among hobbyists and preferred for marine aquarium trade. But due to the emerging use of illegal fishing methods like sodium cyanide and dynamite, the wide population of the blue tang is threatened to extinction. There is a need to conserve this fish. To do this, a through study on the blue tang was conducted.

A group of scientists headed by Dr. Josefa D. Tan-Fermin of the Southeast Asian Fisheries Development Center (SEAFDEC) Aquaculture Department pursued this study. Their main objective is to present important aspects about the blue tang particularly its reproductive biology, embryonic development, larval morphology, and rearing process so that aquaculturists could develop artificial propagation techniques.

About the blue tang
P. hepatus comes under many common names: regal, flagtail sturgeonfish, hippo, or palette tang in the west. The blue tang (along with the yellow tang) is probably one of the most popular marine fishes in the country. Most hobbyists claim that they are easy to keep and are interesting to watch. Unlike most sturgeonfish, this one forages mainly on plankton in the open or far above the bottom of the reef. It has a wild swimming pattern both in the wild and under captivity (aquarium).

Young blue tang lives in free swimming groups (thus, the school of fishes seen underwater) and could be seen individually when they reach sexual maturity, catching zooplankton among corals. When threatened, they flee into the coral and press close to its branches.

In the wild, they feed on zooplankton but in aquarium they accept small, live shrimp and other food such as ground worms and flake foods.

Chracteristics
How different is the male from the female blue tang?

In the study of Dr. Tan-Fermin, samples showed that males are generally larger than females. Other than that, not much of the behavioral instincts are discernable. The study also showed that spawning i.e., fecundity and duration is directly proportional with the age, broodstock diet, lunar periodicity, and temperature under captivity.

Nevertheless, the frequency of spawning is high during lunar phase. For example, the total eggs collected was consistently higher during full moon and last quarter. As to temperature, result showed that highest count of eggs was noted at 280 Celcius and fewer at 24-260 Celcius.

It was also noted that rearing water at salinities 24-28 ppt resulted to a high rate of hatching and survival rate of larvae.

Source: "Reproductive biology, embryonic development, larval morphology, and larval rearing trials in the blue tang" by Josefa D. Tan-Fermin, Luis Maria B. Garcia, Gerald F. Quinitio, and Joebert D. Toledo of the Southeast Asian Fisheries Development Center-Aquaculture Department (SEAFDEC), Iloilo, Philippines.
Photo: http://www.bahamaswildlife.fsnet.co.uk