Using the Blue Gourami in Ethological and Embryological Studies Theresa Thompson Universityof Maryland College Park 20742 Edward 1.Pollak West Chester State College West Chester, Pennsylvania 19380 Laboratory experiments on repro- hours and the fry become free- A 19 or 38 liter aquarium for each Downloaded from http://online.ucpress.edu/abt/article-pdf/43/2/98/38739/4447152.pdf by guest on 25 September 2021 duction and embryological develop- swimming in 3 to 4 days (at pair of blue gouramis ment traditionallyuse frogs or toads 28?C). Partitions (Ben-Gal 1974). We suggest the use The complex mating sequence, Large pieces of slate, aquatic of the blue gourami, Trichogaster which spans several hours, is plants, or artificialspawning grass to trichopterus (Pisces, Belontiidae) easily observed. Subsequently, serve as hiding places for the female. as an alternative subject in such ex- the males exhibit pronounced The smaller the tank, the more hiding periments. The blue gourami is a parental behavior, caring for places are required. member of a family of tropical fishes eggs and fry in a nest con- Fish food (Belontiidae) with many well-known structed of bubbles at the water's Thermostaticallycontrolled aquari- representatives,including the Siamese surface. Observation of sexual um heaters fighting fish (Betta splendens), the and parental behaviors can be Automatic timer for setting light/ paradise fish (Macropodus oper- the basis for laboratory exer- dark cycle (optional) cularis), and the dwarf gourami cises in ethology. Petri dishes, depression slides (Colisa lalia). Because it is an air Eye-droppersor pipettes breathing-fish native to the stagnant Binocular microscope Materials rice paddies and temporary swamps Procedures of South East Asia, no aeration The following materials are equipment is required. Blue gouramis needed: Techniques for spawning blue are easily bred in the laboratory, and they provide thousands of eggs throughout the year. Breeding need not be induced by the administration of exogenous hormones as with most amphibian preparations. The num- erous advantages of using blue gourami eggs for embryological demonstrations include the following: * Blue gouramis are readily avail- able from local pet shops. * The bouyant eggs are trans- parent, permitting the living embryos to be observed through all stages of development with --i-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~---- the use of only a dissecting microscope. * Development proceeds rapidly with cleavage beginning within FIGURE 1. One male (right)and two female blue gouramis (Tnichogastertrichopterus). Note that 30 minutes of fertilization. the dorsal fin of the male is more pointed and longer than that of the female. Only in the male does Hatching occurs within 24 the dorsal fin extend up to or past the caudal peduncle. 98 THE AMERICAN BIOLOGY TEACHER, VOLUME 43, NO. 2, FEBRUARY 1981 gouramis are described in any good tropical fish manual (e.g., Innes 1976). Place one male and one female of approximately equal size into a 19 or 38 liter tank that is visually isolated from other tanks. Breed four or five pairs at once so you will be sure of at least one success. The male and female should be separated by a glass, plexiglass, or commercially available plastic aquarium partition for a one-week acclimation period. Males have longer and more pointed dorsal and anal fins. Mature, gravid females are characterized by a more rounded Downloaded from http://online.ucpress.edu/abt/article-pdf/43/2/98/38739/4447152.pdf by guest on 25 September 2021 abdomen and shorter and more rounded dorsal and anal fins. The water temperature should be main- tained between 26-28?C and illumi- nation regulated to produce a 10- hour dark/14- hour light cycle. A mating sequence typically com- FIGURE 2. Photomicrograph (30X) of an unstained, living blue gourami embryo approximately mences with the male constructing 12 hours after fertilization. a bubble nest at the water's surface; however, lack of a nest does not pre- clude the occurrence of spawning. mately three to four days after utes. Gastrulation becomes evident Mating usually occurs in the late spawning (Miller 1964; Miller and after 3 hours. In 14 hours, melano- afternoon. The light/dark cycle can Robison 1974; Pollak, Thompson, phores appear on the embryo and be shifted to obtain mating earlier or Keener, and Stabler,in press). yolk sac, and optic vesicles are visible later in the day as necessary. The fe- Eggs may be removed from the as evaginations in the living embryo male in spawning condition will bubble nest with an eye dropper and (Hodges and Behre 1953). At this approach the male under his nest, examined under a microscope at stage, the heartbeat, circulation, and and a brief period of courtship will any time during development. Al- somatic muscular movements are follow. A color change from pale to ternatively, the eggs and nest may be becoming visible. Retinal pigmenta- dark blue (accomplished in less than lifted out by slipping a petri dish tion occurs 20 to 22 hours after one minute) accompanies courtship under the entire structure. Initially fertilization. Within 24 hours, the and spawning in both sexes. After it may be difficult to distinguish the embryo's tail lifts away from the yolk the female has approached the nest, eggs from the air bubbles of the nest mass, constituting hatching. Even the male proceeds to wrap his body with the naked eye. Under the micro- though the embryo has hatched, it around the female. The initial scope, however, a large oil globule remains suspended, ventral-side-up, embraces often do not result in can be seen in the eggs. This oil until the yolk and oil masses are re- the expulsion of eggs and milt, but globule keeps the embryo in the duced. Within two to three days subsequent embraces result in the aerated surface layer of the water of hatching, the fry are free-swim- release of up to 100 eggs at a time. along with the bubble nest (Soin, ming (Hisaoka and Firlit 1962). The After each embrace, the male chases Avni, and Dobrachev 1973). Periodi- fry can be reared on finely powdered the female from the vicinity and cally, opaque eggs may appear. fish food and infusoria. Under ideal gathers the eggs into his nest. Several These represent either unfertilized conditions, sexual maturityis reached minutes later, the female will ova or inviable zygotes that are in three to four months. approach the male again and the se- rapidly attacked by fungi. Observa- If a more detailed histological quence is repeated. The entire pro- tion of a single embryo is possible for study is desired, the embryos can be cess may last several hours and in- several hours in a depression slide, preserved in Bouin's Solution at clude between ten and twenty but the embryo must be kept covered specified intervals after fertilization. embraces producing from 1,000 to with water. The first change to occur Clear the embryos in 70% alcohol 2,000 eggs. The male will maintain in the egg will be the formation of a saturated with lithium carbonate. the nest and care for the fry until blastodisk at the animal pole followed Dehydrate in alcohol and toluene, they are free-swimming, approxi- by the first cleavage within 30 min- and embed in paraplast. Section the HOW-TO-DO-IT 99 embryos at 20, and stain with hema- Despite the greater detail apparent HODGES, W.R., and BEHRE, E.H. toxylin and eosin. In these sections, in prepared slides, a relatively com- 1953. Breeding behavior, early em- bryology,and melanophoredevelop- can be examined. The plete descriptive account of normal organogenesis ment in the anabantidfish, Tricho- development of the neural tube, embryogenesis in the blue gourami gastertrichopterus. Copeia 40(2): 100. notochord, and somites can be fol- can be compiled from observation INNES, W.T. 1979. Exotic Aquarium lowed, beginning 8 hours after fer- of the living embryos alone (Hodges fishes. Neptune City, New Jersey: tilization. After 20 hours, retinal and Behre 1953). Although other TFH. MILLER,R.J. 1964. Studieson the social pigmentation can be clearly observed belontiid species could be used for behavior of the blue gourami, Tri- in cross-sections. Sagittal sections such exercises, the blue gourami has chogastertrichopterus (Pisces, Belon- will reveal the development of the several distinct advantages. Unlike tiidae).Copeia (3):469. optic vesicles, divisions of the brain, other species (e.g., Betta splendens), and ROBISON, H.W. 1974. somites, and a section in the optic its eggs are transparent rather than Reproductivebehavior and phylogeny Trichogaster (Pisces, region shows the optic nerve and the opaque. Also unlike Betta splendens, in the genus Anabantoidei). Zeitschriftfur Tier- extent of the differentiation of the blue gouramis are not overly aggres- psychologie34(5):484. neural and pigment layers of the sive and may, therefore, be housed POLLAK, E.I., THOMPSON, T., retina. Under high magnification, in groups when not being bred. KEENER,D., and STABLER,A.L. in press. Observationson multiplemat- individual rods and cones are visible. Blue gouramis are also among the Downloaded from http://online.ucpress.edu/abt/article-pdf/43/2/98/38739/4447152.pdf by guest on 25 September 2021 blue gourami,Trichogaster The lens also exhibits some differen- least expensive, most disease resist- ings in the trichopterus(Pisces, Belontidae).An- tiation. In more posterior sections, ant, and most easily spawned of all imalBehavior. the spinal cord, notochord, and gut tropical fishes. All of these character- SOIN, S.G., AVNI, A.A., and DOBRA- tube with liver diverticulum bending istics contribute to the usefulness of CHEV, V.P. 1973. Adaptivecharac- up around the stomach are all clearly this species in the classroom. teristicsof the developmentof laby- visible. Furtherposterior, the oil mass rinth fishes (Anabantidae).Journal of Ichthyology13(6):1056.