Reveche, Feliciano R. A preliminary study on the reproduction and feeding habits of Dermogenys viviparus Peters. Philippine Agriculturist 11: 181-190.
A PRELIMINARY STUDY ON THE REPRODUCTION AND FEEDING HABITS OF DERMOGENYS VIVIPARUS PETERS
By FELICIANO R. REVECHE
In the summer of 1921, Mr. D. Villadolid, of the Department of Entomology, College of Agriculture, while making preliminary study pn the feeding habits of the fish fauna of Molawin creek, had occasion to collect a few living specimens of Dermogenys viviparus Peters for some biological experimentation. In connection with this study, he found out that this species of fish is a voracious feeder on mosquito larvae. In June, 1922, Mr. W. D. Tiedeman, of the International Health Board of the Rockefeller Foundation, who is working in cooperation with the Philippine Health Service, arrived at Los Baños and made his headquarters at the College of Agriculture, to study malaria condition in Laguna Province and the possibilities of economic control. He interested in fish as a possible means of checking the rapid multiplication of mosquitoes. This fish was then mentioned to him by Prof. H. E. Woodworth, of the Department of Entomology, as possible material to work with. The present is a report on the feeding habits, method of reproduction, local distribution and life history of Dermogenys viviparus Peters. This work was begun in the latter part of July, 1922, and ended at the close of November of the same year. The work was done in the College of Agriculture, University of the Philippines.
1. DESCRIPTION OF DERMOGENYS VIVIPARUS PETERS
Among the Tagalog people the name “Patlay” and “Kansusuit” are synonymous terms, and these are applied to either of the two fish, Dermogenys viviparus Peters or Zenarchopterus philippinus Peters. Dermogenys viviparus Peters, the subject of this paper, is smaller than the other. For the purpose of uniformity, it would be better to adopt the term “Patlay” to Zenarchopterus philippinus Peters and the term “Kansusuit” to Dermogenys viviparus Peters, for the simple reason that the people more commonly use “Kansusuit” for D. viviparus. The term “Patlay” seems to be commonly applied to a fish having long, slender body and capable of swimming very fast; on the other hand, the term “Kansusuit” seems to be applied to small fish with a body not well adapted to swim rapidly. The former is more characteristic of Zenarchopterus philippinus. Peters and the latter to Dermogenys viviparus Peters. Peters (1) described this fish as follows: “Tail fin convex; dorsal fin shorter than annal fin; its first ray inserted behind first annal ray; annal fin inserted after 9/16 of the total length; head semi-flattened; length of head equals 5/16 of the total length; apex of beak yellowish speckled with black, three lines extend from the neck toward dorsal fin, membrane between first and second annal ray, second and third dorsal parts basally spotted behind the operculum with black. Number of scales along longitudinal line 45, transverse 12 to 13, dorsal 10 to 11, annal 14 to 15. Total length 95 mm.”
’Experiment Station Contribution No. 107. I Identified by Dr. A. W. C. T. Herre, of the Bureau of Science. Fowler and Bean, of the Academy of Natural Science of Philadelphia, identified some Philippine specimens which they found labeled Dermogenys viviparus Peters as Hyporhamphus neglectus. It cannot be determined where these specimens originated. To check this however, a bottle of specimens was sent by Mr. W. D. Tiedeman. Field Director of the Rockefeller Foundation in the Philippines, under whom this work was undertaken.
Peters further states, „this species is in its whole body structure very similar to the preceding but considerably larger and one could perhaps consider both as one, but due to the rounded and not two lobed tail fin, as well as to the short dorsal fin, one distinguishes an easily recognizable subgenus of the remaining Hemirhamphus for which reason this name Dermatogenys (Dermogenys) suggested by von Kuhl and van Hasselt was adhered to.
„Dr. Jagor brought this last species from the island of Samar from the river Basey, as is shown in the foregoing specimen 'with living young and developed eggs”.
Distinct external characteristics of both sexes. —
The female, as a rule, is much larger than the male. The average measurement which is taken from 175 specimens of adult females is 73.5 millimeters in length, and the average measurement of the male, taken from 95 adult specimens, is 52 millimeters in length.
The measurement is taken from the tip of the beak to the tip of the tail. All these specimens were caught in the Molawin creek, Los Baños, Laguna.
The caudal fin of the male is beautifully marked with black and pale orange. This marking at the tail is sometimes present in the female, but is not as clear as in the male. The soft rays of the dorsal fin of the male are colored black, and this marking is absent in the female. The ventral fin of the male is also colored pale orange and sometimes little black marks are mixed with it. In the case of the female, the ventral fin is whitish brown, the marks predominating at the soft rays on attaining old age. On the ventral side of the beak of both sexes is a thin fleshy protrusion which runs from the base of the beak to its tip. This protrusion is distinct reddish orange in male, and orange in the female. In the case of the female, there is a protuberance just anterior to the anus which is orange in color. This is absent in the male.
2. THE ALIMENTARY CANAL AND CONTESTS
a. Method of investigation.—
The stomach contents of the fish were determined by dissecting the stomach and making water mounts of its contents. Examination was made under a dissecting microscope (X24) or under a binocular microscope (X40).
b. Digestive system.—
The alimentary canal of the female fish is a simple tubular organ. It is almost pale white in color, and is situated ventrally to the two sacs of the ovary. It may be resolved into three parts. The most anterior part which is a short, small tube is supposed to be the rudimentary oesophagus, and next to it is a dilated and enlarged portion which may be termed the stomach which covers one-third of the length. The posterior part which makes about two-thirds of the length is termed the intestine. The length of whole digestive canal is approximately 34 millimeters. The width varies because the most anterior portion is a small, short tube and next to it portion is a small, short tube and next to it is a dilated part which is the stomach and is approximately 4 millimeters in width. The most posterior part which is the intestine is about 2 millimeters in width. On each ventro lateral side of the alimentary canal are two blood vessels running parallel and terminating; at the posterior portion, about two-thirds of the length. This description of the alimentary canal is taken from one specimen, 92 millimeters in length and 12.5 millimeters in depth.
c. Stomach contents.—
Extensive dissection of the alimentary canal of the fish was done with subsequent examination of the stomach contents. Among those things that were conspicuous in the stomach were mostly portions of body parts of insects and arachnids, such as the wings of insects, legs of spiders, heads and legs of ants, legs and abdomens of small locusts, and exuviae of some kinds immature insects.
3. OBSERVATION OF FEEDING HABITS
Observations of the feeding habits of this fish were made in Molawin creek and in confinement. The fish is provided with a long beak, the lower lip being very much longer than the upper. The fish, therefore, must necessarily be a surface feeder. It could hardly get food at the bottom of the water. If the food happened to be at the edge of a stone or anything that will hinder its progress, the beak is used. Large food is broken into pieces by the mouth before it is swallowed. Oftentimes the young fry are in schools of from twenty to thirty individuals with a few large ones.
They are usually found in a slow current of water or near the water edges in the creek or river. They are found abundantly in quiet, shady places of the creek. This is also true with the adult fish, but the latter is often found in more or less rapid currents in which they oftentimes stay and swim. Most of the time are found on the surface of the water, arranged one after another against the current. They seem to be waiting for their prey to come along with the current of the water. They are very sensitive to noise or disturbances in the water. They react to it positively thinking it possible to be a chance for prey, but are easily frightened at the sight of their enemies. Fighting was observed between individuals in a group over the possessions of a piece of food. If they happened to be of about equal size, they fought hard and strong. The used their beaks as a means of offense and defense.
At night they behave in a very different manner. Most of them are found along the water edges especially in small indentations and stagnant places, swimming around and actively looking for food. They are very active at night, swimming from place to place. This fish is positively phototropic. The writer had occasion to catch a large number of these fish during the night, by attracting them with a lantern into the net.
In pools where this fish was artificially reared, food was given once a day. This food consisted mainly of larvae of both anopheles and culex mosquitoes. Later dried shrimps and white ants or termites were given. The dried shrimps were cut into small pieces before they were given and as such they could be easily swallowed by the fish. Of all this food, the writer found that the fish prefered the anopheline larvae. This might possibly have been due to the fact that the anopheline larva places itself parallel to the surface of the water. It could he, therefore, readily seen by the fish which feeds on things floating on the water. It may be that in nature it prefers water insects as examination of the stomach contents would seem to indicate.
The following table shows how readily anopheles larvae are eaten by this fish when in confinement. It remains to be seen how this would be modified under natural conditions.
TABLE I. Showing the eflicicncy of Dermogenys viviparus items in eating mosquito larvae in an artificial container.
4. METHOD OF REPRODUCTION
Examination of reproductive organs. In the differentiation of the males from the females, the external anatomy was first studied, followed by the dissection for the internal organs. In this connection particular attention was paid to the number of fetuses and developed embryos inside the ovary sacs. The ovary of this fish is V-shaped in form, and is composed of two sacs. Oftentimes, one of these sacs is shorter than the other. Generally, the color of the ovary is silvery with black markings at the side of each sac. The ovary is located dorsally to the alimentary canal, the latter running straight between the two sacs. It extends from the cloaca to the level of the liver. The arrangement of the fetuses inside the ovary sacs can be seen from outside, due to the fact that the sac membrane is transparent. The young fetuses in the sacs overlap each other. The position of the fetuses in the sacs is not the same. Oftentimes the heads of the fetuses point toward the cloaca and at other times they point toward the blind portion of the ovary sacs. The most common number of fetuses is five in each sac. This number increases with the size and age of the fish. In the ovaries there are always found developed embryos and eggs. Measurements of the young fetuses, which supposedly are about to be delivered, were taken. The average length is 18 millimeters.
Table II.¹ — Showing the relative length of the ovary sacs in relation to the total length of the fish with the number of fetuses and embryos found in the ovary sacs.
Specimen Length of fish. Ovary sac Length of Number of fetuses and
number. Number. Ovary sacs. embryos in the ovary sacs.
. Millimeter Millimeter Fetuses Embryos
1 63 1 18 4 7
. 2 18 5 6
2 120 1 35 10 7
. 2 35 11 4
3 50 1 10 — 7
. 2 10 2 4
4 85 1 25 4 3
. 2 20 5 2
5 63 1 20 3 6
. 2 12 7 4
6 60 1 13 5 5
. 2 13 4 6
7 65 1 15 — 3
. 2 15 — 4
8 98 1 25 5 4
. 2 25 5 6
9 60 1 18 3 2
. 2 18 5 3
10 54 1 16 5 9
. 2 16 4 10
11 100 1 30 11 2
. 2 30 5 7
12 75 1 20 4 7
. 2 20 — 6
¹ For lack of space only twelve specimens were noted in this table. It is shown in the above table that the length of the ovary sacs vary according to the length of the females. Generally, the larger or older females have more young fetuses and embryos in the ovary sacs while the smaller or the younger the females the less the number of fetuses. The fact that the young fetuses arc not found in some cases in the ovary sacs of the females may indicate that this fish has a resting period.
5. LIFE HISTORY
Couples of Dermogenys viviparus Peters were confined in separate compartments, fed with mosquito larvae or termites, and kept under close observations. As soon as eachfemale produced young, the latter were transferred to Lot B1, B2, B3, B4, B5, B6, B7 as shown in the succeeding table. Other couples selected from this stock were transferred
and confined in another compartment shown as C1, C2, C3, C4, C5, C6, C7, C8, C9, in the same table.
Table III. Showing intermix between parturition and life history of Dermogenys viviparus Peters under confinement.
It is worthy of note that a single female gave birth to 5 sets of 5 young each at intervals averaging about 8 days and that these young gave birth to their first group of 2 or 3 young at the average age of only 83+ days.
a. Notes on the stages in the development of the young embryo.¹
1. In the first stage of development, the young embryo is enveloped by a thin membrane (called the chorion, in mammals). The eyes are already developed. The tubular heart is already functioning. On the dorsal part of the embryo running from the most posterior part of the head are black dots which terminate at the anterior part of the dorsal fin. This stage is characterized by the presence of a large amount of yolk.
2. In the second stage, the same characteristic features are found as in the first stage, but differ only in that in the second stage the embryo proper is larger, while the yolk is much diminished in bulk and quantity.
3. The third stage is practically the same as the second stage, but the yolk is distinctly reduced in size and quantity, and the embryo is very much larger. There are black dots appearing very conspicuously in that part of the body mentioned above. The eyes are larger.
4. In the fourth stage, the membrane or chorion which envelopes the embryo seems to bulge out but the young embryo is still coiled in the ovary sacs of the mother. The yolk is greatly diminished in quantity by this time.
5. In the fifth stage, the young fetus appears to be complete in its organs of locomotion. The black dots appearing more prominently. On each side of „the young fetus there is a lateral line which begins from the sides of the pectoral fins and terminates at the caudal fin. At this stage of development, small protrusions are visible on the upper beak just anterior to the eyes one on each side. An experiment was was performed to find out whether the young fetuses would live when artificially taken out from the ovary sacs of the mother. The result was that they only lived for two or three days, and in most cases died after three days. Food was given but they would not eat.
The young are born alive. They come out one by one through the cloaca. When outside of the mother’s body, they immediately swim to the surface of the water to get air. They look sluggish and inactive, but they can hardly be caught with the hand unaided. The average length of the newly born young is nineteen to twenty millimeters. At this stage, the beak is a little projection at the lower lip. The orange and black markings are absent on both sexes and their distinct color is whitish gray. An attempt made to measure the growth of some of these young failed because they were lost after three days. However, they grew one or one and one-half millimeters in length a day.
As the young fish grows, its activity increases. The young easily penetrate the pools and water edges seeking food The female fish attains the mature stage when it is about fifty to sixty millimeters in length, and the male attains 'maturity at about fifty-five millimeters. At this stage of development, they begin to mate. The markings at this stage become distinct on both sexes so that one can easily tell the males from the females.
¹ Notes:- It must be noted that beginning from the first stage the young embryo appears to be transparent to the unaided eyes but however, the most discernible organsare the organs of sight and functioning heart.
The female starts giving young at the age of 81 to 85 days. She gives two or three young at the first time. As the female ages, the number of young increases. This generalization is based upon the observation obtained from females reared in confinement. Commonly, an old female will give five young at each parturition, and the maximum number one has been noted to produce is ten.
The record of one female (female A,) shows that from the time she was placed in confinement up to the time she was placed in confinement up to the time she was accidentally killed a period of 75 days, she was able to produce 42 young. So far this work tends to show that the fish is able to live under artificial conditions and can reproduce a number of young if care is given.
The natural habitat of this fish is the ditch, creek, river or other small stream. In Balanac river near Magdalena, Laguna, this fish was observed and was found to inhabit places of slow current or stagnated places in the river.
b. Ability to live and reproduce under artificial conditions:
Dermogenys viviparus Peters lives and reproduces fairly well in pools which have free circulation of water, and has been found to thrive just as well in stagnant water. The size of the pool where this fish was reared is about four by five meters. It is divided into several lots. In lot 1, enclosed by a wire screen, twenty females and twelve males were introduced in August, 1922, and in November, 1922, the number of the fish in this lot altogether was 332. Most of the females that were introduced in this lot were 73 millimeters long and when they were counted again and examined, some of them had grown to 130 millimeters in length. The males did not exceed 67 millimeters in length. A single female fish under these conditions of confinement produced 15 offspring in the course of three months which, if there were no period of sexual inactivity, would mean 60 for the year. Bearing in mind that the rate of bearing offspring increases with age, this number will be considerably increased.
One diseased condition of Dermogenys viviparus Peters was encountered in the pools. The attacking organism (a fungus) belongs to the genus ACHLYA¹ which is a free living organism in the water. It grows anteriorly near the eyes of the fish at the beginning and finally affects the eyes. The fish becomes blind and dies afterward. It appears as a white filamentous growth at the head of the fish and is easily recognized. However, it is rarely found attacking this fish.
8. DISTRIBUTION IN LAGUNA PROVINCE
The fish is more or less evenly distributed through the province of Laguna. The fish may be found in the upper courses of most rivers and small streams in the province. The writer found it in abundance in Molawin creek of Los Baños, in ditches in Masiit in Calauan, in ditches in the town of Magdalena, and in ditches and creeks in San Juan, Loñgos. This fish does not seem to frequent the lower courses of the streams. In all the places visited by the writer the fish was not observed in places near the mouth of streams. In Molawin creek this fish is very scarce within about a kilometer of its mouth, but is plentiful towards the source. In Laguna de Bay and small lakes of San Pablo such as Bunot, Tikiw, Kalibato, and Sampaloe, the fish is not found.
¹ Statement from Prof. F. P. Prof. F. P. McWhorter of the Department of Plant Pathology, College of Agriculture. Experiment Station Contribution No. 108.
Association with other fish.—
In the creeks, this fish is seen associated with another very small fish which belongs to the genus Gobio. The latter fish stays mostly at the bottom of the water, and wherever Dermogenys viviparus Peters is present the former scenis to be present too. In a pool where this fish was confined, dalag (Ophiocephalus stratus) was introduced, to find out, whether the Dermogenys would be eaten by it. Some of the Dermogenys were found wounded, but none were eaten. This fish lives fairly well with top minows (Gambusia affinis) in pools. In a one-half barrel filled with water where both were confined in the insectary of the Department of Entomology, they have not attacked each other.
SUMMARY AND CONCLUSION
Dermogenys viviparus Peters is locally found in the province of Laguna in more or less shady places of old streams, ditches, creeks, and rivers. The fish is a highly beneficial fish because of its predacious habits on mosquito larvae. It is a surface feeder and feeds voraciously on anopheline larvae. A small “Kansusuit” (Dermogenys viviparus Peters) has eaten 78 anopheline larvae in 5 hours and 38 minutes. The development of the young embryo may be divided into five stages. The young are born alive. The small fish is generally more active than the large ones.
The female Dermogenys matures at the age of 81 to 85 days. She produces two or three young the first time, and as she grows older more young are given out at each parturition. The older female usually gives five young every eight days. This may vary at different seasons of the year and there may be a period or periods of sexual inactivity each year. The fish lives and reproduces fairly well under artificial conditions.
White ants or termites are the best food if it is is reared artificially. Dermogenys viviparus Peters has some possibilities as a so-callod “mosquitofish”. It is a surface feeder by nature and, in confinement, will eat anopheles mosquito larvae readily. It has been known to maintain itself in places needed and other voracious fish are present. In spite of all this, it has not been demonstrated as yet to be of economic importance in mosquito control although it may be under some peculiar conditions. The fact that the fish is so widely distributed and yet is not found in any one place in sufficient numbers to control breeding, shows that there must be many natural enemies to be overcome. It is true that the removal of grass and weeds from the edges of streams may help by making food more easily available. However, in a section of Molawin creek which is rocky and contains no weeds, we found anopheles breeding in spite of the presence of the fish. Further work is necessary to demonstrate the practical possibilities of the use of this fish in mosquito control.
The author is greatly indebted to Mr. W. D. Tiedeman for his valuable help in the preparation of this paper, also to Dr. A. W. C. T. Herre of the Bureau of Science and Dean C. F. Baker of the College of Agriculture.
The ilustrations were drawn by Mr. Aniano Estores.
PETERS, Monatsberichte d. Akadeime d. Wissenschaften zu Berlin. Page 132, 1865.
Plate I A. Stages in the development of the young embryo.
1. First stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 mm.. . . . X-S
2. Second stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 3.5 mm… . X-%
3. Third stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..~7 mm.. . . . X-S
4. Fourth stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12 mm.. . .X-8
5. Fifth stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18 mm.. . . X-3
B. Dorsal view of the head of a newly born Dermogenys viviparus Peters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . X-15
C. Lateral view of a newly born Dermogenys viviparus Peters . . . . . . X-3
D. Ovary sacs showing the arrangement of the young fish and matured eggs inside . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . . . . . . . . . . . X-4
E. Ovary sacs showing the young fish inside, nearly ready to be delivered . . . . . . . . X-4
F. Ventral view of the entire alimentary canal and its relation to the ovary sacs of the female Dermogenys viviparus Peters. . .. X-2
1. Lateral view of the male.
2. Lateral view of the female.
Plate III. D. viviparus Peters, showing the arrangement of scales and fins.