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Chapter One
BIOLOGY AND ECOLOGY
Noel B. Solis*
For the culture of any species to evolve from tradition or art to science, basic information on the biology of the species is required.
This paper reviews current information on Penaeus monodon including taxonomy, morphology, distribution, and bionomics and life history. The last covers reproduction, development of embryo, larva up to adult, spawning, food and feeding, and physiology.
Problems that have cropped up with the intensification of prawn culture, e.g. discharge of pesticides from grow-out ponds, are highlighted. Other conflicts such as the conversion of mangroves and other estuaries, considered nursery grounds of various marine fauna including P. monodon , into fishponds; overexploitation of wild spawners with no stock assessment data; and indiscriminate throwing away of other prawn and finfish f r y from wild collections in favor of P. monodon f r y could adversely affect the ecology of mangroves and other marine ecosystems.
TAXONOMY
The genus Penaeus Fabricius (1798) was placed on the Official List of Generic Names in Zoology as Name No. 498 upon the discovery and description of Penaeus monodon by John Christ Fabricius in 1798 (Mohamed 1970). With the revision of the specific name monodon by Holthuis, the two species have become stabilized and the name P. monodon is generally accepted for the present species (Hall 1961, Mohamed 1970, Motoh 1981). No subspecies are currently recognized for this species and P. monodon manillensis (Villaluz and Arriola 1938) proved to be based on an abnormal specimen of P. semisulcatus (Mohamed 1970, Motoh 1981).
*Research Associate of SEAFDEC Aquaculture Department
Definition
The taxonomic definition of the giant tiger prawn is as follows: Phylum Arthropoda Class Crustacea Subclass Malacostraca Order Decapoda Suborder Natantia Infraorder Penaeidea Superfamily Penaeoidea Family Penaeidae Rafinesque, 1815 Genus Penaeus Fabricius, 1798 Subgenus Penaeus Species monodon
Scientific name: Penaeus (Penaeus) monodon Fabricius,
It has four synonyms: Penaeus carinatus Dana, 1852 P. caeruleus Stebbings, 1905 P. monodon var. manillensis Villaluz and Arriola, 1938 P. bubulus Kubo, 1949
The FAO names are giant tiger prawn (English), crevette geante tigree (French), and camaron tigre gigante (Spanish).
The term shrimps and prawns are common English names used synonymously due to the absence of systematic basis to mark a distinction (Wickins 1976, Holthuis 1980). In an attempt to clarify the issue, Holthuis (1980) traced the origin of the names shrimps and prawns and its usage in various countries. In general, shrimps refer to the smaller animals and prawns to the larger ones, while according to Food and Agriculture Organization (FAO) Convention, shrimps refer to marine
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Fig. 1. Lateral view of
P. monodon
showing important parts (Motoh 1981)
Antennularflagellum
Antennal
scale Third maxilliped
Pereopod (Walking leg) Antennal flagelum
Pleopod (Swimmeret)
Uropod(Tail fan)
Telson
Sixth abdominal
segment
Abdominal segment
Adrostral carina
Epigastric spine
Hepatic spine
Hepatic carina
Gastro-orbital carina
Antennal spine Rostrum
ABDOMEN
CARAPACE
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Fig. 2. Geographic distribution of Penaeus monodon (Motoh 1981)
A live giant tiger prawn has the following characteristic coloration: carapace and abdomen are transversely banded with red and white, the antennae are greyish brown, and the pereopods and pleopods are brown with crimson fringing setae. In shallow brackish waters or when cultured in ponds, the color changes to dark and, often, to blackish brown (Motoh 1981).
DISTRIBUTION
The giant tiger prawn is widely distributed throughout the greater part of the Indo-Pacific region, ranging northward to Japan and Taiwan, eastward to Tahiti, southward to Australia, and westward to Africa (Racek 1955; Holthuis and Rosa 1965; Motoh 1981, 1985).
In general, P. monodon is distributed from 30°E to 155°E in longitude and from 35°N to 35°S in latitude with the main fishing grounds located in tropical countries, particularly Indonesia, Malaysia, and the Philippines (Motoh 1985, Figure 2).
The fry, juvenile, and adolescent inhabit shore areas and mangrove estuaries, while most of the adults inhabit deeper waters down to 162 m (Motoh 1985). Distribution is sparse as evidenced by a few prawns collected at any one time.
Biology 7
hepatopancreas; and the abdominal lobe which lies dorso-lateral to the intestine and ventro-lateral to the dorsal abdominal artery. The oviducts originate at the tips of the sixth lateral lobe and lead to the external genital opening at the coxopods of the third pair of pereopods.
The thelycum, located between the f i f t h pair of pleopods, consists of an anterior and a pair of lateral plates. It receives the spermatophores during mating. In penaeids, the thelycum may be classified as closed or open type, and P. monodon belongs to the closed type.
Motoh (1981) compared the detailed internal reproductive organs of P. monodon with those of P. setiferus and P. indicus.
Sexual maturity. Motoh (1981) defined sexual maturity as the minimum size at which spermatozoa are found inside the terminal ampoule of the males and inside the thelycum in the females. The later indicates that copulation or the transfer of spermatophores from the male to the thelycum of the female has taken place. On this basis, Motoh (1981) reported that wild P. monodon males possess spermatozoa at 37 mm carapace length (CL) (about 35 g body weight or BW) and females at 47 mm CL (about 67.7 mm BW) although pond-reared prawns were mature only at 31 mm CL (about 20 g BW) and 39 mm CL (about 41.3 g BW), respectively. Primavera (1980) reported the presence of spermatozoa in both pond-reared and wild P. monodon males of 40 g body weight (38.5 mm CL), a minimum of 63 weight (about 46 mm CL) for wild females, and about 40 g body weight (41 mm CL) for pond-reared prawns.
From the viewpoint of reproduction, Primavera (1985) emphasized the importance of gonadal maturation and the presence of fully developed spermatozoa with tail or spike. Motoh (1981) reported that sperms without tail were observed in wild P. monodon males of smaller size or about 37 mm CL, while Primavera (unpubl.) recently made mention of 10-month old pond-reared P. monodon with immature (spikeless) sperm.
Ovarian maturation stages. The maturation of the ovary has been categorized into five stages, the classification of which is based on ovum size, gonad expansion, and coloration (Villaluz et al 1969, Primavera 1980, Motoh 1981, Tan-Fermin and Pudadera, in press). Figure 4 illustrates the stages of ovarian development in P. monodon.
Biology 9
Fig. 3. Reproductive system of Penaeus monodon (Motoh 1981)
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Fig. 4. External appearance of the ovaries of Penaeus monodon at different stages of maturity as seen through the dorsal exoskeleton (modified from Primavera 1983)
Stage I and V (undeveloped and spent stages). Ovaries are thin, transparent, and not visible through the dorsal exoskeleton. Histological studies show that the ova averaging 36 microns are covered with a layer of follicle cells and the larger ones have nucleus and yolk granules (Motoh 1981). Tan-Fermin and Pudadera (in press) described Stage I as the perinuclear stage composed of perinuclear oocytes (46-72 microns) negatively stained with AB-PAS and Sudan Black. Oocytes bigger than 55 microns are enveloped by a single layer of follicle cells.
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Similar features are observed in the spent stage which also contains some yolky oocytes, thicker follicle layer, or irregularly shaped perinucleolar oocytes (Tan-Fermin and Pudadera in press).
Stage II (developing stage). Referred to as early maturing stage, the ovaries are flaccid and white to olive green in color, and discernible as a linear band through the exoskeleton. The developing ova averaging 177 microns in diameter have yolk granules and cells believed to be nutritive bodies (Motoh 1981). The cells referred by Tan-Fermin and Pudadera (in press) as cystoplasmic inclusions are composed of small granules of glycoproteins, medium-sized globules of lipoglycoproteins, and few large lipid droplets.
Stage III (nearly ripe stage). Ovaries have glaucous color with the anterior portion thick and expanded. They are very visible through the exoskeleton, particularly at the first abdominal segment, when viewed against the light (Motoh 1981, Tan-Fermin and Pudadera, in press). The ova average 215 microns in diameter.
Stage IV (ripe stage). The ovary classified as ripe (mature) stage is diamond-shaped, expanding through the exoskeleton of the first abdominal segment. The isolated ovary appears dark olive green, filling up all the available space in the body cavity (Primavera 1980). Motoh (1981) reported the presence of a characteristic margin of peripheral rod-like bodies, the apexes of which radiate from the center of the egg. The ova average 235 microns in diameter. Tan-Fermin and Pudadera (in press) characterized this stage to consist mostly of yolky oocytes (288-408 microns) with additional rod-like bodies which contain acid and basic mucopolysaccharides but without lipids.
In some cases, ovaries are observed to be discontinuous, i.e., white in color in either the anterior or posterior portions with olive green color in the opposite ends. This condition is referred to as partially spent ovaries.
At present, these categories are used in the selection of wild spawners and prove to be generally effective. Prawns of Stage IV are used in hatchery operations. In the field, handling of the prawn for visual observation of the ovary color, size, and shape can not be avoided and can be stressful to the animal.
Biology 13
Fig. 5. Eggs of P. monodon at various embryonic developmental stages. (A) newly spawned eggs, (B) 4-cell stage (about one hour after spawning), (C) morula stage (about 1.8 hours after spawning), (D) early embryonic nauplius, (E) late embryonic nauplius, (F) embryonic nauplius about to hatch (Motoh 1981)
A
C
E
B
D
F
the antennular flagellum to the tip of the telson. Under laboratory conditions, postlarvae become benthic on the sixth day of the post-larval stage. In natural conditions, the megalopa enters the nursery ground. The carapace length of megalopa varies between 1.2 and 2.3 mm.
Juvenile. The earlier juvenile stage has transparent body with dark brown streak on the ventral side as in the megalopa. Motoh (1985) described the earlier juvenile stages as follows: (1) relatively shorter sixth abdominal segment compared to the carapace length, (2) greater body size, (3) complete rostral spine formula, (4) complete gill system, and (5) benthic behavior.
Biology 15
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In the later stage, the body becomes blackish in color and bulky, and the rostrum has 7 dorsal and 3 ventral spines. The juvenile crawls using the pereopods and swims using the pleopods as in adults. The carapace length varies from 2.2 to 11.0 mm.
Motoh (1981, 1985) and Motoh and Buri (1980, 1981) have described the early postmysis stages of the giant tiger prawn.
Adolescent. This stage resembles the adult prawn. Sexes are now distinct beginning at 11 mm CL. The minimum size of males possessing a jointed petasma is about 30 mm CL and the minimum size of females possessing adultlike thelycum is about 37 mm CL. The carapace length of the adolescent varies between 11 and 34 mm.
Subadult. This stage is the onset of sexual maturity. The male possesses spermatozoa in its terminal ampoules. The thelycum of the female now contains spermatozoa. At this stage (30 mm CL), females grow faster and migration from nursery to spawning grounds begins. In the course of migration, first copulation takes place between males and females having a minimum of 37 mm and 47 mm CL respectively.
Adult. This stage has appendages very similar to the subadult and is characterized by the completion of sexual maturity. It differs only with the subadult in size and habitat. Males possess spermatozoa, and females start to spawn offshore although a few spawn in shallow water. A second or more copulations may occur in majority of the species. Major habitat is the offshore area up to about 160 m depth.
The maximum total length recorded was 336 mm (Holthuis 1980), while a mature female of 307 mm from Madagascar was reported by Crosnier (1965) as cited by Mohamed (1970) and 330 mm total length by Racek (1972). In the Philippines, the largest male ever found was 71 mm CL while the female was 81 mm CL with 270 mm body length or 240 g weight (Motoh and Buri 1980). Carapace lengths of adults vary between 37 and 71 mm in males and 47 and 81 mm in females.
The life history phases of the giant tiger prawn are summarized in Table 1, and the diagram of the life history is shown in Figure 7.
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Longevity
There is no reliable method developed to determine the age of an individual prawn. Villaluz et al (1969) believed that the life span of P. monodon is one to two years; Motoh (1981) estimated it to be about one and a half years for males and about two years for females. Mohamed (1970) cited Srivatsa (1953) who reported that the life span of prawns (including P. monodon ) in the Gulf of Kutch is 12-14 months.
Spawning
Spawning is the release of eggs and spermatozoa by the female prawn into the water for fertilization. The spermatophore which contains the spermatozoa is deposited in the female thelycum during copulation long before spawning. Although there is no report on the actual process observed in the natural condition, the spawning behavior of P. monodon has been documented based on laboratory observations (Villaluz et al 1969, Aquacop 1977, Primavera 1980, Motoh 1981). Discussion on spawning behavior is described in detail by Primavera (this volume).
In the Philippines, Villaluz et al (1969) reported that no P. monodon spawners below 50 mm CL have been collected in the Panguil Bay area, and concluded that first spawning occurs at 56 mm CL. However, Motoh (1981) reported that spawning females ranged from 47 to 81 mm CL and came in four size groups, namely: 48-50; 60-62, 66, and 72 mm CL. This finding indicates that P. monodon spawns four times in its life span and probably has multiple spawnings in a single season (Primavera 1980). In Orissa, India, Rajyalakshmi et al (1985) reported gravid P. monodon with size range of 100-250 g (about 54-76 mm CL) off the Paradip Coast.
Specific location of spawning area depends greatly on secondary evidence like the presence of abundant spawners and larval forms. In the Philippines, P. monodon spawns in the sea close to the coast (Delmendo and Rabanal 1956) or in the mouth of the bays with water depth of about 20 m but mostly spawns in offshore water to about 70 m (Motoh 1981). Hall (1962) calculated a more specific spawning area of P. indicus with P. monodon at about 18-36 m deep. In the Paradip Coast, Orissa P. monodon spawns at 30-40 m
Biology 19
Fig. 7. Diagram
of
the
life
history
of
the
giant
tiger
prawn,
P. monodon
(Motoh 1981)
ESTUARINE
INNER LITTORAL
OUTER LITTORAL
Juvenile
7 m 20 m depth
Adolescent
Megalopa
Subadult
Adult
Spawning
Eggs
Nauplius
Protozoea
Mysis
Biology 21
(Rajyalakshmi et al 1985), and in the coastal waters of Tungkang, Taiwan at 10-40 m (Su and Liao 1986).
In the Philippines, spawning of P. monodon is year-round but there seems to be two peak spawning seasons in a year: February-March or July and October-November although these vary from year to year (Motoh 1981). Hall (1962) reported February to April in Singapore; Rajyalakshmi et al (1985) in October through April corresponding to the post monsoon stability in the water movement and the increasing salinity in Orissa Coast, India; and Su and Liao (1986) from June to December in Taiwan.
Food and Feeding Habit
Hall (1962) generally considered penaeids to be omnivores with P. monodon in particular preferring crustaceans, vegetable matter, polychaetes, molluscs, fish, and insects. Thomas (1972) supported this finding and explained that mud and sand found in the gut were accidentally ingested. Villadolid and Villaluz (1951) reported that the fry stage of sugpo relishes plankton ( lablab ) food. Marte (1980) reported that P. monodon food also consisted of crustacea (small crabs and shrimps) and molluscs, making up 85% of ingested food. The remaining 15% consisted of fish, polychaetes, ophiuroids, debris, sand, and silt. This indicates that the giant tiger prawn is more of a predator of slow-moving benthic macroinvertebrates rather than a scavenger or detritus feeder. Kuttyama (1973) observed that debris composed of mud and organic matter constituted the main portion of the stomach content while crustaceans ranked next in quantity. Similar food items were also observed by Su and Liao (1986). All these findings suggest that P. monodon is more of a carnivore with preference for crustaceans particularly when in the natural environment, but it also feeds on other available organisms including algae.
P. monodon seems to have increased feeding activity during ebb tide (Marte 1980) and shows some food preferences during seasonal variations of food (Kuttyama 1973). This species feeds by seizing the food with its pinchers and pushing food to the mouth to nibble (Villadolid and Villaluz 1951). Undigested food is defecated four hours after ingestion (Marte 1980).
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