Gill Raker Morphology in Some Red Sea Fisl,}6S of Different Feeding

JKAU: Mar. Sci., vol. 6, pp. 93-122(1415 A.H./1995 A.D.

Gill Raker Morphology in Some Red Sea Fisl,}6sof Different Feeding Preferences

OSAMAA. ABUZINADAH Dept. of Biological Sciences,Faculty of Science, King Abdulaziz University, leddah, Saudi Arabia

ABSTRACf. Samplesof twenty-six different Red Seafish specieshave been collected from areas near Jeddah. For studying the gross morphology of the gill rakers bucco-pharyngeal cavity have been dissected. Also, entire gut- contents; especially that of the stomach, have been examined to determine the nature of food. This is an attempt to correlate betweenshape andnature of the gill raker with the nature of food. It is noticed that, carniv6rous fishes are characterized with their few and limited numbers of rakers which slightly varies among the same species. Rakers of the outer most row are well-developed and longer than that on the following row. All rakers are provided with fine spinules which may serve in seizing and preventing escapeof smooth prey. Plankton-feeder fishes are generally characterized with numerous and elongated rakers. These rakers carries numerous, fine spinules which are varied in shape. Rakers serve in straining water current entering pharyngeal cavity for seizing food items. Chonos chonos fishescharacterized from the rest of plankton-feeder fishes with their interdigitated rakers. Tliese inter- digitate rakers form a unique and effective sieve-like structure which serve in retaining of fine food items. In general, gill rakers of herbivorous fishes is shorter than that of plankton-feeder fishes. They always carry numerous fine spinules. They serve as filter which prevent passing of matters attached to the marine plants and sea weeds, to the branchial chambers. The preceding case also coincides with the caseof Scarus blochi; coral- feeding fish. Rakers on this fish permit the entry of the grinding food matters (items) into the gill cavity,

93 Gill Raker Morphology in SomeRed SeaFishes. 95

TABLE Contd

About 3 to 4 fishes of each specieshave been collected during a period of three weeks. They have been transported from either the fish market or Saudi Fish Co. to the laboratory. There, they have been carefully dissected.Firstly, operculum was removed. Then, cut was made through the angle of the mouth and jaws moved awayso as.to expose the bucco-pharyngealcavity.' Gill archs arrangement and the relation between them have been noticed. Both of the first and second gill archs removed away and washed. For preparing their illustrations, they have beenpreserved in 10% of formaline. Illustration have been made to show the existed differences between the two gill arches. To study feeding habits of sampled fish, stomachshave been cut and its contents have been taken which help in studying nature of food, especiallyin plankton-feeder fishes.

Observations

I. Nature of Food and Feeding Habits Stomachcontents of severalfishes of the samespecies have been examined to de. termine the nature of food for eachspecies. According to the type of food they con. sume, fish specieshave been divided into the following groups:

A) Carnivorous Fishes This group have been divided into 3 subgroups: 1. Predacious (Piscivorous) fishes. 2. Crustacean-feederfishes. 3. Carnivorous fishes feeding on a mixture of animal diet

B) Plankton-feeder Fishes It is in turn divided into 2 groups 1. Zooolankton feeder. Gill Raker Morphology in SomeRed SeaFishes. 97

C. Herbivorous Fishes This category includes 4 fish speciesnamely; Siganus rivulatus, Acanthurus velifer, Mugil auratus and Mugil seheli. Their stomachcontents comprise fragments of vari- ous marine plants and seaweeds. Besides, there are some algae specieswhich differ from fish to another. D. Coral-feederFishes Only one scarid species, Scarus blochi, have been sampled among the sampled species. As, it was the most abundant speciesof coral-feeder category during the period when this study was carried out. The intestine and fore-gut contained ground corals and stonesmixed with fragmented marine plants and algae. Also, some parts crustaceananimals have been observed. The fish obtain their food by scrapingthe surface of stonesand corals. So, it is thought that crustaceais taken by fish occasion- ally as they are found on the algae which grow on the corals and stones.

II. Gross Morphology of the Gill Rakers A. Gill Rakers of the Carnivorous Fishes 1. Gymnosarda unic%r Each of the gill archesof Gymnosardaunic%r consistsof one piece. It carries two rows of rakers, one on eachside. Rakers on the anterior row of the first gill arch differ from that on the posterior row and also that on the rows of the following arches. Their counts range from 28 to 30. Their lengths vary between 8 and 16 cm which equal about half length of the opposite gill filaments. They are conical in shape with tapering tops. Each carries numetous triangle knobs with acute and sharp edges. These knobs have no definite arrangement, and distancesseparating them vary. Al- though, under microscope they look like saw-shape(Fig. 1, A & B). /~ A s( \ lII :..1 't \, ~ ,/~Y/{(ili/t!;I!;"/,'~I" 0 2 , ., G) 80mm

FIG. 1: A. A diagram for the first gill-arch of the carnivorous fish Gymnosarda unicolor. B. An enlarged gill-raker.

Rakers on the posterior row of the first gill arch, and the rest of rows, appear as small conical knobs with slightly bending tops. Their counts on each row varies from 16 to 19. The limitation in their number may be contributed to the increment of their diameter. Each knob carries fine, acute, needle-shapedspinules which are scattered on their surface (Fig. 2, A & B).

'"~ Gill Raker Morphology in SomeRed SeaFishes. 99

0 2 0 2 I .I I .I CD 20mm 100mm

FIG. 4: A. A diagram for the posterior gill-arch of E. affinis. B. An enlarged gill-raker.

arranged in clusters. Each of these cluster contains between3 to 5 spinules which are separated with small and variable distances(Fig. 5, A & B and Fig. 6, A & B).

A B

\ / 0 2 CD 7~ FIG. 5: A. A diagram showing the morphology of the first gill-arch of the carnivorous fish Sphyraena forsteri. B. Enlargl;d gill-rakers.

0 2 0 2 ..I ..I 0 20mm 300 mm

FIG. 6: A. A diagram for the posterior gill-arch of the fish S. forsteri. B. Enlarged gill-rakers. 4. Epinephqlus areolatus Gill arch has bow-shapeand formed of one piece, so, it seemmore stout. The first gill arch is characterized with the rakers of the anterior row. Their count varies from 20 to 22. They are similar in shape but varies in size. The longest is that lies on the Gill Raker Morphology in Some Red SeaFishes. 101

J- 140mm FIG. 9: A. A diagram for the first gill-arh of the carnivorous fish, E. [outi. B. Enlarged gill-rakers. !

Gill rakers of the posterior row on the first gill arch as well asthe following rows are less strong than the predescribed ones. They differ also in shape. They have a knife shape with bandied ends. The longest raker lies in the middle part of the gill arch. Their internal surfacesare covered with small, fine and acute spinules which are arranged in groups or clusters. Each contains between 3 to 5 spinules. It is noticed that these spinules cover the top of the rake not only on the internal surface (Fig. 10, A &B).

0 2 0 I 0' ? 30 mm 70mm

FIG. 10: A. A diagram for the posterior gill-arch of the above fish B. An enlarged gill-raker.

6. Plectropomus maculatus Gill arches in this speciesare formed of1 one piece. Anterior of gill rakers of the first gill arch varies between 18 to 20. Limit tion in their number on sides of the arch may be attributed lack of rakers. It is also noticed that there are between two and three rakers relatively long in size. These r~kers lie on the curved (bending) portion o!the arch. Except these ra~ers, the re.stqf rakers are almostsimil~r and equal in SIze. They are separated wIth equal dIstances. Each raker carry fine, acute and triangle-shapespinules. These spinulescov~red the upper part of the internal surface of the long rakers, while, they cover all of tmeinternal surface of the small ones (Fig. II,A&B). Number of rakers on the posterior row of the first gill arch, and that on the following rows on the archesbehind are equal. ~ut, they differ from 1hat on the anterior Gill Raker Morphology in SomeRed SeaFishes. 103

80mm FIG. 13: A. A diagram showing the morphology of the first gill-arch of the carnivorous fish Chorinemus lysan. B. An enlarged gill-raker.

A B p-..:,:~' ,..,,. , .~ "" ~

8. Alepes djedaba Gill rakers of the anterior row on the first gill arch are characterized from that of the preceding fish, which belongs to the samefamily. Their count ranges from 30 to 33. Also, they are shorter and thinner. Thus, they carry less number of spinules than that carried with rakers of Chrinemuslysan. The spinules are scattered on the rakers and they are directed outward. Rakers of the anterior row differ from that of the posterior row. They are very short and have thick and broad bases, they have different shapes.They have triangular, pyramidal or leafly shapes.Contrary to rears of the precedingfish, they do not lie at right angle to the gill arch. They are covered with fine, acute and needle-shapespinules (Fig. 15, A & B).

A B II , 1 :!:=-~-/? / 0 2 I .. 80 mm FIG. 15: A. A diagram representing the first gill-arch of the carnivorous fish Alepes djedaba. B. An enlarged gill-raker.

/} Gill Raker Morphology in Some Red SeaFishes. 105 arm of the arch. The first one is big oval or pear like in shape, it extend along the breadth of the arch. The second one is small oval-shape. It lies on the upper side of the arch, i.e. on the medial surfaceof the arch. The two types are arranged in alterna- tion where two big rakers surround a small one. On the short arm of the arch, big rakers of the first type, are present. The two types are covered with small, fine and needle-shapedspinules with tapering ends (Fig.18, A & B).

..I 20mm

FIG. 18: A. The posterior gill-arch of the fish C. bajad. B. An enlarged gill-raker.

10. Caranx sexfasciatus The first gill arch have two forms of gill rakers. On the anterior row existsfine and long rakers, their lengths are about one-fourth of the length of the opposite gill filaments. Their counts vary between 34 to 37. They have sharpblade shape which bent inward. Each of the rakers carries numerous, fine triangle-shapedspinules with tapering and acute tips. These spinules appear as they have adjacent and connected bases(Fig. 19, A & B).

180mm FIG. 19: A. A diagram representing the first gill-arch of the carnivorous fish Cranx sexfasciatus. B. An enlarged gill-raker.

In contrast, the posterior row of rakers on the first gill arch as well as the rows on the following gill arches contain limited number of rakers. Raker's count per row ranges from 12-15. To a great extent, they are all identical and have stubby, stout more or less rectangular in shape and flattened. They lie at an inclined position on the side of the arch. They c-arrynumerous triangle-shaped lamellae with acute tips. Distances separatingbetweeD'~akers greatly vary (Fig. 20, A& B). Gill Raker Morphology in Some Red Sea Fishes. 107

0 2, 0... 2 ~O"' m 240mm'

FIG. 22: A. The posterior gill-arch of the abovefish. B. An enlarged gill-raker. arches. Their count varies between 18 to 20. They \Laryin size, the longer lie on the long arm while the shorter lie on the short arm of the gill arch. They are needle in shape with tapering ends. Contrary to most of the preceding fish species, they are slightly bent outward. These rakers are supported with pyramidal protrusions, from inner side. These protrusions arise from the mid line of the arch, they are smooth. Absence of spinules may be compensatedwith shapeand tapering ends of the rakers (Fig. 23, A & B).

A B

2 140mm FIG. 23: A. A diagram showing the morphology of the first gil1-archof the carnivorous fish Gerres

gyreus. B. An enlarged gil1-raker. Rakers on the rest of the row, rather than the most anterior row, are slightly more numerous. Their count per row varies from 20to 23. But, they are noticeably shorter and thicker than that on the anterior row. Their tips are less tapering and so they seemas inclined conicals. There are no protrusions supporting them as in the case'of the anterior row, They are also smooth (Fig. 24, A & B).

0 2 0 2 ..I ..I itO m m 140 m m FIG. 24: A. The posterior gill-arch of the above fish. B. An enlarged gill-raker. Gill Raker Morphology in Some Red SeaFishes. 109

14. Lethrinus nebu/osus Raker of the two rows on the first gill arch do not differ from that of the rest of rows on the following arches. They are generally stubby and stout. They have either pyramidal or mace-top shapes.The only differences between rakers of the anterior row and that on the rest of rows is that the extemaljront of that rakers, exceptthe tip, is naked. While their tips are covered with fine and needle shape spinules. On the other hand, rakers on the other rows are totally covered with these spinules, which are numerous on the tip. In general, raker counts per row rangesbetween 15 and 17 (Fig. 27, A & B). ~

0 '2 ..1 80mm FIG. 27: A. The morphology of the first gill-arch of the carnivorous fish Lethrinus nebulosus. B. An enlarged gill-raker. 15. Paraupeneusbarberinus Anterior row of the rakers on the first gill arch is characterized with fine and saw- shape rakers. Their count ranges!from 30-33. They are slightly bent outward, and their external surfaces are serrated. Serration is close on the upper part and it be- comes steadily wider as it moves to the middle. Length of these rakers are about one third of the length of the opposite filaments. Rakers of the posterior row and that of the rows on the three gill archesbehind differ from that of the anterior row. They are stubby and s.tout,but they are thick and with flattened tips. Thus, their number is smaller than that of the anterior row. Whereas, distance separating rakers on the posterior row are more or less equal to that on the anterior row. In general, surfacesof theserakers are covered with numerous, fine and needle-shapespinules (Fig. 30, A & B).

0 2. 0 2 25mm 200m m FIG. 28: A. A diagram representing the morphology of the posterior gill-arch of the above fish B. An enlarged gill-raker. Gill Raker Morphology in SomeRed SeaFishes. 111

A B iLL \,,:=--~~,I/ 0 2 0 2 I ..I 30mm 400mm

FIG. 32: A. A diagram for the posterior gill-raker of the above fish B. Two enlarged gill-rakers.

17. Be/one choram There are two types of rakers. The first one is very minute and hardly canbe seen. Rakers on this type lie on most of the sidesof the arch. The secondtype is relatively bigger. This type are restricted on the hind part of the long arm of gill arch. They are minute and convex knobs, which are covered especially on their tips, with very minute and acute spinules. These spinulesare very minute even they can hardly be detected except by touch (Fig. 33, A & B).

140 m m FIG. 33: A. A diagram showing the morphology of the first gill-arch of the carnivorous fish Be/one choram. B. An enlarged gill-raker.

B. Gill Rakers of Plankton FeederFishes According to stomachcontent analysisof four different speciesthey were differen- tiated into two categories: 1. Zooplankton feeder fishes: Includes Rastrelliger kanagurta, Caesisstriatus and Clupeasirm. 2. Phytoplankton feederfishes: Includes only one species; Chanoschanos.

1. Rastrelliger kanagurta Each of the gill archescarries two rows of rakers. The anterior row of rakers on the first gill arch differs from all the following raker rows. They are clearly long and pro- jects,into the oral cavity. So, they easily appear when the mouth is opened, ev~n ill Raker Morpho.logyin SomeRed SeaFishes. 113

2. Caesiostriatus The first gill arch carries two row of different rakers. Rakers of the anterior row differ from that on the following rows behind. Characteristically, they are elongate. Their lengths reach about one third of the length of the opposite gill filaments. Their number per row is about 33. They seemas they arise in groups from the tips of small knobs. Each group include between 3 to 4 fine and long rakers with acute ends. It is noticed that their ends are often directed outward. They are closely set at their bases, while they are distant to the tops (Fig. 37, A & B)..

Q ? 220mm FIG. 37: A. A diagram showing the morphology of the first gill-arch of the zooplankton feeder fish Caesiostriatus. B. An enlarged group of gill-rakers. Rakers of the posterior row on the first gill arch are similar and identical to that of the rows of the following arches. They are in form of bony knobs. Their counts per row vary between 13 to 14. Each of these knobs carries between 3 to 5 very minute spinules. These spinules are hardly detected except with touch. Rakers have wide basesand distances separating them along arch are almost equal (Fig. 38, A & B).

A B~ ~~,.,L 'I' ""-..

0 2 0 2 I ., I ..1 bOmm 160mm

FIG. 38: A. A diagram representing the posterior gill-arch of the above fish. B. An enlarged gill-raker.

3. Clupeasirm There are four gill arches, each consistsof two pieces. Each arch carries well-developed rakers arranged in two rows. Rakers of the ~nterior row differ from that on the following row behind. They are elongate and slender with tapering ends. They are very long on the first gill arch, while they decreasegradually in length on the following arches. Approaching the last arch, it carries the shortestrakers. The internal Gill Raker Morphology in SomeRed SeaFishes. 115

0 2 I .I 100 mm FIG. 41: A. A diagram showing the morphology of the first gill-arch of the phytoplankton feeder fish Chanos chanos. B. An enlarged group of gill-rakers.

0 2 0 2 I .I I .I 30mm 100 mm FIG. 42: A. A. The posterior gill-arch of the samefish. B. An enlarged group of gill-rakers.

1. Siganus rivulatus Each of the gill archescarries two rows of similar and identical rakers 22 to 25 in number. They look like a spines with broad basesand more or less tapering ends. They have fine needle-shape with very fine serration toward external and internal sides. Distance separatingrakers on the row is variable (Fig. 43, A & B and Fig. 44, A&B). 2. Acanthurus velifer There are four archeseach carrying two rows of rakers. These rakers vary in shape

A B

0 2 ..I 440m m FIG. 43: A. A diagram for the first gill-arch of the herbivorous fish Siganus rivulatus. B. An enlarged gill-rakers. 1 Gill Raker Morphology in SomeRed SeaFishes. 117

Their count per row varies between 32 and 36. Their basesare attached, near their tips, they are distant. Rakers of the posterior row on the first gill arch and that of the rows on the following archesare similar and have the samelengths. While that of the anterior row are long. Their length equal about two folds the length of the others (Fig. 47, A & Band 48, A & B).

FIG. 47: A. A diagram showing the morphology of the first gill-arch of the herbivorous fish, Mugil seheli. B. Three emerged gill-rakers.

0 2 0 2 I. I I .I itOm m 100mm

FIG. 48: A. The posterior gill-arch of the same fish. B. Three enlarged gill-rakers.

4. Mugil auratus Gilliakers of this speciesare slightly different from that of Mugil seheli.Rakers of the anterior row on the first gill arch are much longer and bent outward. Their internal edges are serrate, with spines. These spines are small, pointed with triangular bases.They resemble the shape of the rakers. Rakers lying on the following arches are as long as those of the preceding fish. But, they are less in number. Thus, they seemmore stout. They are serrated at their external edges,while that of the anterior row, were internally serrated{Fig. 42, A & Band 43, A& B). Gill Raker Morphology in Some Red SeaFishes. 119

0 2 200 m m FIG. 51: A. A diagram representing the first gill-arch of the cor~l-feeder fish, Scarusblochi. B. An enlarged gill-ra~r.

Q ? 0 2 30mm 300mm

FIG. 52: A. The posterior gill-arch of the abovefish. B. Three enlarged gill-rakers.

Discussion During the present study, samplesof twenty six different fish specieshave been collected from areas near Jeddah, Red Sea. For identifying and studying the gross anatomy of gill rakers buccophrangealcavity have been dissected. Also, contents of stomachsand entire gut; in caseof stomachlessfishes, have beenexamined to determine the nature of food for each fish species.This study have been carried out as an attempt to correlate the shapeand structure of the gill raker with the nature of food. According to the predescribedobservations, it was noticed that carnivorous fishes, piscivorous, crustacean-feederas well as fishes which feed on mixture of animal diet, are characterized by their limited number of rakers. The number of rakers slightly varies among the same species.This coincides with Suyehiro's (1942) observation during his ins tanding study of fishes of JapanSea. It is also observed that rakers of the anterior row on the first arch are more developed and carry. minute spinules, while rakers on the following rows behind are shorter. Their shortnessvaries from speciesto another but they also carry spinules that may help in seizingof preys; especially slippery, slimy and smooth preys and prevent their escape.These observations resemblesthat of AI-Hussaini (1947), Abdulgalil (1988~and Abuzinadah (1990), as

1" Gill Raker Morphology in Some Red SeaFishes. 121

; (1947b)The feeding habits and the morphology of the alimentary tract of some teleosts living in the neighbourhood of the Marine Biological Station, Ghardaqa, Red Sea. Publications of the Mar. Bioi. Stat., Ghardaqa (Red Sea),no. 5: 4-61. (1949) On the functional morphology qf the alimentary tract of some fish in relation to differ- encesin their feeding habits: anatomy and histology. Quarter. J. Microscop. Sci., 90: 109-139. and Bayoumi, A. (1967) On gill rakers of some pelagic fishes from the Gulf of Suez. Publ. Mar. Bioi. Sta. Ghardaqa. Egypt. 5: 90-100. Gohar, H. and Bayoumi, A.R. (1950)Queted from Abuzinada, Q.A. (1990). and Latif, A.F.A. (1959) Morphological studies on the gut of some scarid and labrid fishes. Publications of the Marine Biological Station. AI-Ghardaqa (Red Sea). No. 10: 145-190. Martin, N. V. and Sandercock, F.K. (1967) Pyloric caeca and gill raker development in lake trout, Sal- velinus nsmaycushin Algonquim Park, Ontario. J. Fish. Res. Board of Canada,24: 965-974. Mohsin, O. (1962)Comparative morphology of the alimentary canals in certain groups of Indian teleosts. Act Zoologica, Stockholm. 43: 79-133. Kapoor, B., Smit, H. and Verighina, I.A..(1974) The alimentary canaland digestion in teleosts. Adv. Mar. Bioi., 13: 109-239. Randall, J.E. (1983) Red SeaReef Fishes. Immel Publishing, London. Reshetnikov, Yu (1961) On the connection between the amount of gill-rakers and the nature of feeding in chars of the genus Salvelinus. Zoologicheskij Zhurnal, 40: 1574-1576(in Russian). Suyerhiro, Y. (1942)A study on the digestive systemand feeding habitsoffish. Jap. J. Zool., 10: 303-560.