The embryological development of the tilapiine fishes

Transcription

1 Rochester Institute of Technology RIT Scholar Works Theses Thesis/Dissertation Collections The embryological development of the tilapiine fishes Michelle Katz Follow this and additional works at: Recommended Citation Katz, Michelle, "The embryological development of the tilapiine fishes" (1988). Thesis. Rochester Institute of Technology. Accessed from This Thesis is brought to you for free and open access by the Thesis/Dissertation Collections at RIT Scholar Works. It has been accepted for inclusion in Theses by an authorized administrator of RIT Scholar Works. For more information, please contact

2 ROCHESTER INSTITUTE OF TECHNOLOGY A Thesis Submitted to the Faculty of The College of Fine and Applied Arts in Candidacy for the Degree of MASTER OF FINE ARTS The Embryological Development of the Tilapiine Fishes By Michelle Katz Date: August 1988

3 Approyals Adviser : Mr. Gl e n Hintz Date : $. "-( I _...::..==.::.-::=='----- Glen Hintz - As s oclate Advisor : Date : ~ ' 15 I S ~ ASsoclate Advisor : Date : '2l - :" -i?x Special Assiatant Dean for ~jr.du~te Date: 1 IT I' Dean, col~fge of to the Affairs : Hr. Robert Habnitz I Robert Wabnitz nr, R. Doolit tle / Richard Doolittle Hr. Philip W. Bornartb Phil ip W. Bornar th ===5th;Ef~~=' s~~~~ ~;~:: an~'fd\l~arts : Dr 'R:~:t th ~ 'J~;::~~:;in r I I, Michelle Katz, hereby grant permission to the Wallace Memorial Library/ of RIT to reproduce my thesis in whole or in part. Any reproduction will not be f or commercial use or profit. Date: a"j l44i" I f&-/?

4 INTRODUCTION The purpose of this thesis is to visually document the embryological development of two different species in two different genera of the Tilapiine fishes. These include Tilapia mariae (spotted tilapia), a substrate spawner and Oreochromis aureus (blue tilapia), a maternal mouth brooder. Historically, these fishes were lumped into the genus Tilapia however, recently Ethelwyn Trewavas split the Tilapiine fishes into three separate genera based mostly on their reproductive behavior and development. Differences in genetic structure, biochemistry, feeding behavior and biogeography will not be considered at this time. Those species which were substrate spawners were placed in Tilapia, those which were maternal mouth brooders into Oreochromis, and those which were paternal mouth brooders into Sarotherodon. Sarotherodon was not documented due to difficulties encountered in breeding and sampling. Based on Haeckel's hypothesis that ontogeny recapitulates phylogeny, I have examined the morphological differences and 2 similarities of the embryological development of these fishes. Although Haeckel's theory was rejected in part, current biological information suggests that ontogenic data are useful in discerning evolutionary relationships. Hopefully, the information gathered in this study will provide insights into some of the evolutionary relationships among the Tilapiine genera.

5 MATERIALS AND TECHNIQUES Selecting the appropriate materials and technique for a particular illustration is prerequisite to any effective scientific illustration. Such an illustration should help explain and and clarify a designated piece of research or information therefore, visual factual accuracy is essential. In the process of selecting materials and technique, consideration must be given to the type of publication in which the illustrations are to appear. In most instances, scientific data reaches the science community through journal publications. It is essential that the image be clearly legible when printed. It is therefore imperative to acquaint yourself with the requirements and characteristics of the publication and select materials and methods accordingly. Illustrating the embryological development of fishes requires a great deal of experimentation. In this study, the purpose was to observe any internal or external morphological differences in the features of developing fish. Therefore, several methods were explored to ensure consistent, optimal conditions for observatiom of the developmental stages. What follows is a brief description of the processes which proved to be most effective with regard to specimen observation and preparation of the final illustrations. All stages of embryological development from hatch (tail-free) through pre- juvenile were carefully observed through

6 a dissecting microscope and notes were taken about the general appearance with regard to translucency, pigmentation, counts (no. of spines and rays of fins, no. of somites / myomeres) and measurements (eye size, length, and head / body depth). The same information was recorded from the adults however, magnification was not necessary because of their size. Black and white enlargement photographs were shot through a compound microscope equipped with a Nikon camera attachment to be used as visual references. There were several problems associated with photographing fish larvae. Specimens were preserved in formalin to maintain structural integrity. It was essential that all specimens remain intact because they must be numbered and cataloged to allow for comparison between the illustration and its preserved specimen at any time. This concern for specimen preservation made setting up the appropriate light source for each stage of development a challenge. As development progressed, the light source was increased to compensate for the increasing opacity of the specimens, and as the light source was increased, the larvae began to dehydrate. The time and cost associated with photography must also be considered. Two photographs were taken of each specimen with a different depth of field and light source; one illuminating internal structures and the other focused on external features. Reflections can not always be avoided and information is often distorted or lost. It is up to the artist and the researcher to

7 surface." decide if the quality of the photos and the wear and tear on the specimens justifies the time and cost of creating a reference. After the film was developed, I decided that the photographs were not detailed enough to use soley as references. I then turned to the camera lucida for preparation of the initial outlines at 12x magnification. " A camera lucida is an image-forming device attached to a dissecting microscope which enables the viewer to make enlarged dimensionally correct drawings of three-dimensional objects by tracing the outline of the object directly onto a drawimg surface." 3 It uses a reflector to direct light from the illuminated subject and drawing surface directly into the artist's eye. Again, dehydration and other physical damage was risked. Distortion around the edges of the field of view was a potential problem but was easily avoided by placing the specimen in the middle of the field and drawing it in two or more overlapping segments. A mechanical pencil with 2B lead on white paper was used for these drawings. I chose a mechanical pencil because it didn't require sharpening thereby reducing the chance of specimen dehydration. The lack of variations in line weight are not a problem at this point. The 2B lead on white paper provides a good contrast so that you can easily distinguish the drawing from the super-imposed image of the subjects. "Since the images of subject and drawing surface are super-imposed on the artist's retina they appear to overlap in the artist's field of view so that the artist can trace the outlines directly onto the drawing 4

8 These outline drawing roughs were then completed with help of the dissecting scope, notes and photographic references. At this point, I decided to increase their size an additional 4x with an accurate photocopier so that the final illustrations could later be reduced to 64% for clearer publication. Finally, it was time to begin the final drawings. By this time, I had decided to make half-tone carbon dust drawings on kid finish bristol board for the developmental stages. Carbon dust can give an illusion of transparency and illuminate subtle differences and similarities in pigment, opacity and translucency more effectively and in less time than pen and ink. Kid finish bristol is relatively inexpensive and provides enough tooth to hold the carbon dust without adding any confusing textures to the drawing. Photocopies of the final roughs were transferred to bristol board and final drawings of the developmental stages were completed with the aid of the dissecting scope, notes, and reference photographs. Final pen and ink drawings of the adult stages were prepared on Letramax 4000 from the notes and direct observation. Pen and ink is the traditional medium for ichthyological illustration because it clarifies the counts and is the easiest and least expensive to reproduce. Letramax 4000 allowed me to scratch my ink lines without damaging the board and erase lines with a fluid imbibed eraser.

9 Diagrammatic representations of morphology and development of larval and adult stages of a typical fish are provided on the next page to aid in understanding of the following descriptive data. They are taken from page nineteen of Carl Bond's Biology of fishes.

10 ^contracted1,. pectoral budl intestine or gut preanal flnfold ouglobuie dorsal IInfold ventral flnfold " myoseptum YOLK-SAC LARVA cnromatophi olfactory bud maxillary mandible preopercle opercle cleithrum pectoral fin liver LARVA stellate (expanded) cbxomatophore anlage of dorsal fin incipient rays of anal fin eticulatlons in vertebral column dorsal fin spinous soft nuchal region occiput pelvic fin. (thoracic) v ' vent anal fin caudal fin isthmus axillary appendage pelvic fin (abdominal) caudal peduncle Diagrammatic representation of morphology and development

11 DATA Tilapia mariae Plate 1 Twenty-five to twenty-seven (25-27) pairs of somites are visible. Eye pigmentation is increasing progressively with size and the choroid fissure and lens become clearly recognizable. Embryonic head glands are present and otoliths can be seen within the auditory vesicle. The caudal f infold is completely free of the yolk sac and preanal and ventral finfolds are separated by the intestine and anus. The anlage of dorsal, anal and caudal fins appear in stage B. The yolk sac remains relatively the same size, although a change in shape can be noted in stage C as the pectoral fin bud begins to protrude. Pigmentation spots on the yolk sac begin to increase in size. Plate 2 Twenty-five to twenty-seven (25-27) pairs of somites are visible. Eyes continue to increase in size and become completely saturated with pigment. Embryonic head glands are still present. Finfolds continue to differentiate and a full complement of caudal fin rays can be noted by stage F. The mouth and anus break free and olfactory buds can first be noticed in stage D. The yolk sac begins to decrease in size as a result of absorption and its pigment is more organized. Pectoral fins begin to significantly enlarge. Bony structures of the head (maxilla, mandible, opercle preopercle) become visible. Contracted chromatophores first appear on the dorsal aspect of the head in stage D.

12 PLATE 1 B i mm. Stages in the Development of Tilapia mariae All specimens are illustrated at 16X original size A. 3 days, 1 hour and 20 minutes post-spawn B. 3 days, 13 hours and 30 minutes post-spawn C. 4 days, 1 hour and 15 minutes post-spawn

13 PLATE 2 i mm. D. E. F. 5 days, 6 days, 6 days, 23 hours and 10 minutes post-spawn 11 hours and 25 minutes post-spawn 23 hours and 15 minutes post-spawn

14 Tilapia mariae Plate 3 Twenty-four to twenty-six (24-26) pairs of somites are visible. Eyes continue to increase in size. Embryonic head glands begin to degenerate in stage H and completely disappear by stage I. By this time, fin rays have appeared in the dorsal, anal and pectoral fins. Chromatophores are still present on the head. The yolk sac continues to absorb. Plate 4 The somites have differentiated into approximately twenty-four (24) myomeres. Eyes are fully developed although they continue to increase slightly in size. Chromatophores are still present on the dorsal aspect of the head and have begun to migrate caudally. Fins are beginning to resemble their adult form and a full complement of fin rays is attained. The vertebrae have developed and are clearly visible. The yolk sac continues to decrease in size and becomes almost completely absorbed. Plate 5 The adult total length is 183mm. Twenty-seven to thirty (27-30) scales are present along the lateral line. Fin counts are as follows: dorsal fin - sixteen (16) spines and thirteen (13) rays, caudal fin - sixteen (16) rays, anal fin - three (3) spines and eleven (11) rays, pelvic fins - one (1) spine and five (5) rays, and pectoral fins consist of about thirteen (13) rays.

15 PLATE 3 ^*- H mm. G. H days, 8 days, 8 days, 23 hours and 10 minutes post-spawn 1 1 hours and 25 minutes post-spawn 23 hours and 5 minutes post-spawn

16 PLATE 4 J. 9 days, 1 1 hours and 5 minutes post-spawn K. 10 days, 11 hours and 20 minutes post-spawn L. 1 1 days, 1 1 hours and 40 minutes post-spawn

17 PLATE 5

18 DATA Oreochromis aureus Plate 1 Twenty-five to twenty-seven (25-27) pairs of somites are visible. Eye pigmentation increases rapidly and the lens and choroid fissure are easily distinguished. Otoliths can be seen within the auditory vesicle. The caudal finfold is completely free of the yolk sac and the pre-anal and ventral finfolds are separated by the intestine and anus. The anlage of the dorsal, caudal and anal fins appear in stage B. Pectoral fin buds appear in stage C. The yolk sac remains relatively the same size and its pigmentation is minimal. Head size and structures increase rapidly in comparison to the standard length. Plate 2 Twenty-five to twenty-seven (25-27) pairs of somites are visible. Eye size and pigmentation continue to increase. Olfactory buds appear. The mouth and anus break through and bony structures of the head (maxilla, mandible, preopercle, opercle) begin to take shape. Incipient rays of the caudal fin appear and finfolds continue to develop. Pectoral fin buds begin to develop. Chromatophores appear on the dorsal aspect of the head and begin to migrate caudally.the yolk sac begins to decrease in size as a result of absorption and its pigmentation remains relatively light.

19 PLATE 1 Stages in the Development of Oreochromis aureus All specimens are illustrated at 16X original size A. 2 days, 18 hours and 20 minutes post-spawn B. 3 days, 6 hours and 50 minutes post-spawn C. 3 days, 18 hours and 35 minutes post-spawn

20 PLATE 2 i mm. D. E. F. 4 days, 4 days, 5 days, 7 hours and 10 minutes post-spawn 18 hours and 35 minutes post-spawn 6 hours and 20 minutes post-spawn

21 Oreochromis aureus Plate 3 Approximately twenty-five (25) pairs of somites are visible. Eyes are completely saturated with pigment and their size continues to increase. Bony structures of the head continue to develop. Dorsal and caudal fin rays have developed and the pectoral fin bud is growing rapidly. The intestine is becoming convoluted and the presence of a swim bladder is indicated. More chromatophores appear and have migrated to the dorsal and ventral aspects of the body. The yolk sac continues to decrease and yolk sac pigmentation is minimal. Plate 4 The somites have differentiated into approximately twenty to twenty-four (20-24) myomeres. Eyes are fully developed although they continue to increase slightly in size. Chromatophores have migrated over the full body of the fish and a pigmentation pattern is developing on the caudal fin. Fins are beginning to resemble their adult form and a full complement of fin rays is attained. The vertebrae have developed are are visible. The yolk sac is significantly reduced and is almost completely absorbed. Plate 5 The adult total length is 206 mm. Twenty-nine to thirty-one (29-31) scales are present along the lateral line. The fin counts are as follows: dorsal fin - sixteen (16) spines and thirteen

22 PLATE 3 G. H days, 6 days, 7 days, 16 hours and 45 minutes post-spawn 7 hours and 10 minutes post-spawn 18 hours and 40 minutes post-spawn

23 PLATE 4 K I MM. J. K. L. 8 days, 8 days, 9 days, 6 hours and 50 minutes post-spawn 18 hours and 45 minutes post-spawn 7 hours and 15 minutes post-spawn

24 PLATE 5 (0 O O Pi 3 o EH 0) co CD c "^ (D C W,^ 0) a c

25 three Oreochromis aureus (13) rays, caudal fin - sixteen 16 rays, anal fin - (3) spines and ten (10) rays, pelvic fin - one (1) spine and five (5) rays, pectoral fin is approximately thirteen (13) rays. DISCUSSION AND CONCLUSION The most obvious visible differences between the developmental stages of the two species are the size and shape of the yolk sacs and the presence of head glands in Tilapia mariae. Tilapia mariae contain three pairs of embryological head glands. These are prominent structures which appear on the heads of embryos prior to hatching and disappear when the fish begin to swim. Each gland secretes an extremely elastic mucus which attaches the developing fish to the substrate (cultural media or lake substrate) so that it won't be swept away in the current. Embryological head glands are not a necessity of Oreochromis aureus because they are maternal mouth brooders. The female parent holds the eggs in her mouth until the young are free-swimming and after this, at night and in case of danger. "The researchers and insights of members of the school of behavioral physiology at Tubingen have shown that mouth brooding has evolved in cichlids from substrate brooding." 6 There are several other different subtleties in appearance between these two species. To describe them would defeat one of

26 the purposes of scientific illustration which is to decrease the length of the text for journal publication. Illustrations serve the purpose of several pages of description. "Scientific illustrations of fish eggs and larvae are an indispensable component of any descriptive work, providing a visual reference of form and structure which is not possible to express by written descriptions and measurements In fact, many laboratory teaching manuals require students to draw the subject they are studying because drawing is an extremely effective means to remembering and understanding a subject. Illustrations are the most preferred and frequently used aid for taxonomic identification of fish larvae. "They facilitate identification by emphasizing distinctive but often subtle morphological characters and allow for comparison of features at different developmental stages and with morphologically similar taxa. 8 " During the research part of this project, I discovered that far more than comparisons of morphological characters of developing fish larva is needed to provide insights into evolutionary relationships among the Tilapiine genera. Structural similarity is easily misinterpreted. When organisms share characteristics, there are three possible explanations. "One animal may have been derived from the stock to which the other belongs; the two may belong to different stocks that have arisen from a common ancestor; or the forms may represent individuals of widely separated lines in which similar traits have developed 9 convergently. " Comparative developmental morphology is only one

27 of the many scientific disciplines that a systematist utilizes in producing as accurate an estimate as possible of the evolutionary relationships under investigation. Further information is needed from areas such as genetics, biochemistry, behavior and biogeography to bring this study to any concrete conclusions. Hopefully, the illustrations and research from this aspect of the project will provide one of the links necessary for completion of this investigation.

28 FOOTNOTES 1 Ethelwynn Trewavas, Tilapiine Fishes of the Genera Sarotreradon, Oreochromis. and Danakilia (New York: Cornell Univ, Press, 1986), p. 13. Harvey E. Jordan and James E. Kindred, Textbook of Embryology (New York:D. Appleton-Century Company, 1948) p Zbigniew T. Jastrzebski, Scientific Illustration: A Guide for the Beginning Artist (New Jersey: Prentice-Hall, 1985) p Ibid. 5Elbert Ahlstrom and Geoffrey Moser, "Embryological Head Glands of the Cichlid Fish Aequidens portalegensis, " Copia, Vol , p Trewavas, p B. Laroche, B.Y. Sumida, andb.b. Washington. Ontogeny and Svstematics of Fishes: illustrating Fish Eggs and Larvae (Berkeley: Univ. of CA Press, 1983), p Ibid. "Barbara J. Stahl, Vertebrate History: Problems in Evolution (New York: McGraw Hill Book Co., 1974), p. 99.

29 BIBLIOGRAPHY Ahlstrom, Elbert H. and Geoffrey Moser. "Characters Useful in Identification of Pelagic Marine Fish Eggs." CalCOFI Rep. Vol. XXI (1980), pp Bardach, John E., Karl F. Lagler, and Robert R. Miller. Ichthyology. New York: John Wiley and Sons, Inc., Bond, Carl E. Biology of Fishes. Philadelphia: W. B. Saunders Co., Brinley, Floyd J., and Leroy Eulberg. Embryological Head Glands of the Cichlid Fish Aequidens portalegrensis. " Copia. Vol. 1 (1953), pp Cech, Joseph J., and Peter B. Moyle. Fishes: An Introduction to Ichthyology. New Jersy: Prentice-Hall, Inc., Hardy, Jerry D., and Alice Mansueti. Development of Fishes of the Chesapeake Bay Region: An Atlas of Egg. Larval, and Juvenile Stages. Maryland: Univ. of MD Press, Jastrzebski, Zbigniew. Scientific Illustration: A. Guide for the Beginning Artist. New Jersy: Prentice Hall, Inc., 1985.

30 BIBLIOGRAPHY CONT. Jones A. J. "The Early Development of Substrate Brooding Cichlids (Teleostei: cichlidae) with a Discussion of a New System of Staging." Journal of Developmental Morphology. Vol.136 (1972), pp Jordan, Harvey E.,and James E. Kindred. Textbook of Embryology. New York: D. Appleton-Cectury Company Inc., Papp, Charles S. Manual of Scientific Illustration. California: American Visual Aid Books, Stahl, Barbara J. Vertebrate History: Problems in Evolution. New York: McGraw Hill Book Co., Trewavas, Ethelwynn. Tilapiine Fishes of the Genera Sarotheradon. Oreochromis, and Danakilia. New York: Cornell Univ. Press, 1986.