Structure and function of the third maxillipeds of the banana prawn Penaeus merguiensis

The functions of the third maxilliped of Penaeus merguiensis de Man are described. It has a 6-segmented endopodite which is used in feeding, grooming and possible pheromone reception. In feeding, large pieces of food are gripped by the stout spines on inner borders of the ischia which hold them to the mouth so that particles can be torn off and ingested. All the distal segments have long setae used in grooming chelate pereiopods and the antennules. In mature males there is a tuft of about 300 slender setae at the end of the propus, but its function remains obscure.     

Statolith implantation in the banana prawn Penaeus merguiensis

Specimens of Penaeus merguiensis de Man were captured between February and May 1981 from intertidal creeks and beaches of Cleveland Bay, Townsville, Australia, using a 15 m seine net. The statocyst of P. merguiensis resembles that of other macrurans in that it is a dorsal invagination of the basal antennular segment lined with groups of sensory hairs. The statolith is composed of sand grains implanted by the prawn from the substratum which must be done after every moult. Implantation begins within 90 min of ecdysis and has 3 phases: sifting; digging and finally eye withdrawal which pushes the sand grains into the statocyst chamber.     

Setal development,moult-staging and ecdysis in the banana prawn Penaeus merguiensis

Specimens of juvenile Penaeus merguiensis de Man (1888) were captured by seine netting from the shores of Cleveland Bay, Townsville, Queensland Australia between February 1980 and November 1981. Accurate determination of moult cycle stage can be achieved rapidly by microsopical examination of setal development in an excised whole pleopod. Four major stages and 5 substages within premoult were clearly defined. The rate of setogenesis varies along the length of a pleopod, precluding the examination of only one specific location on the pleopod for accurate moult cycle staging. The process of ecdysis lasts for no more than 40 s.     

Effects of endogenous and some exogenous factors on the activity of the juvenile banana prawn Penaeus merguiensis

In conditions of alternating light and dark, juvenile Penaeus merguiensis de Man are more active during the dark phase. The rhythm persists in continuous dim red light, but not in continuous bright white light. The period of circadian rhythm shown in continuous dim red light varies between individuals from 22.75 to 26.0 h, with a mean of 23.8 h. The response of prawns to an artificially produced tidal situation is mediated by the presence or absence of water flow. No endogenous component of this tidal rhythm was demonstrated. There is an irregular short-term rhythm (period 2 to 3 h). It is suggested that this allows starved prawns to conserve energy.     

Field estimates of growth and mortality of juvenile banana prawns (Penaeus merguiensis)

Postlarval and juvenile Penaeus merguiensis de Man from the Embley River estuary on the north-eastern Gulf of Carpentaria were sampled every 2 wk from September 1986 until August 1989, using a small beam trawl. Settlement of planktonic postlarvae peaked during the pre-wet season (October to December), and declined through the wet season (January to March). Using length-frequency analysis between 12 and 14 cohorts of juvenile prawns were identified each year. Length-frequency analysis and modal progression were used to derive growth rates during the estuarine phase of the life cycle. Growth rates, which could be described by a linear model, ranged from 0.63 to 1.65 mm CL (carapace length) wk^-1. Growth rates were positively influenced by water temperature and negatively influenced by prawn density. Salinity had no effect on growth rates. Prawns spent between 6 and 20 wk in the Embley River before emigrating offshore from the estuary. Weekly instantaneous rates of natural mortality (M) ranged from 0.23 to 0.94, and in general were lowest during the dry season (July to September) and highest during the pre-wet and wet seasons. Only temperature significantly influenced mortality rates, with mortality rates increasing with temperature. By projecting juvenile growth rates forward through time, we established which cohorts contributed to the offshore fishery each year. In 1987 and 1988 the April fishery consisted of prawns which had settled in the river before the end of January each year. Slow growth rates during the pre-wet season of 1988 meant that only cohorts that were settled before early December 1988 contributed to the fishery in April 1989. Whether a cohort contributes to the fishery depends on the settlement date, water temperature and prawn density.     

Oocyte development in the kuruma prawn Penaeus japonicus

Female kuruma prawns (Penaeus japonicus Bate) with undeveloped, early developing, developing, nearly ripe and ripe ovaries, were collected from Ise Bay, Japan, in 1984. Oocyte development of the kuruma prawn was classified into ten stages according to morphological characters, namely: (1) synapsis stage, (2) chromatin nucleolus stage, (3) early perinucleolus stage, (4) late perinucleolus stage, (5) oil globule Stage I, (6) oil globule Stage II, (7) yolkless stage, (8) yolk granule stage, (9) prematuration stage, and (10) maturation stage. The synapsis stage is a multiplication stage. The chromatin nucleolus stage, early and late perinucleolus stages are previtellogenesis and primary growth stages. Oil globule Stage I is an initial stage of primary vitellogenesis and secondary growth. Follicle cells on the oil globule Stage I oocytes expand rapidly and reach maximum size during oogenesis. Yolk granule stage oocytes are in the initial stages of secondary vitellogenesis. Strongly acidophilic yolk granules accumulate within basophilic vesicles of the cytoplasm. The yolk granules are first concentrated in the inner part of the cytoplasm, then gradually spread to the periphery. Cortical crypts, which are separated from the oocyte cytoplasm by the cytoplasmic membrane, are situated outside of oocyte cytoplasm. Germinal vesicle breakdown (GVBD) is initiated in the late phase of prematuration and continues until the late phase of maturation immediately prior to spawning. At the beginning of the maturation stage, the oocytes are ovulated, after which the nuclei further shrink and migrate out-wards. After ovulation, meiotic division of the ovarian oocyte progressed up to the metaphase of primary maturation division. Finally, the meiotic metaphase is visible just beneath the cytoplasmic membrane in the mature oocyte. Though ovulation is synchronous within the same ovary, GVBD is not completely synchronous. Ovulated mature oocytes have many club-shaped cortical crypts in the peripheral part of the cytoplasm and contain extensive accumulations of yolk granules dispersed throughout the cytoplasm. The apical end of the club-shaped cortical crypts and cytoplasmic membrane are coated by the vitellin envelope in the mature oocyte.     

Carotenoids in the tiger prawn Penaeus esculentus during ovarian maturation

Female Penaeus esculentus Haswell were collected by 15 to 20 min duration trawls during 1990. Carotenoids were analysed in the digestive gland, abdominal muscle, the remainder of the body (hereafter called integument) and ovary of prawns in Stage 2 through Stage 4 (fully mature) of maturation. The only oxycarotenoids (xanthophylls) identified were astaxanthins or astaxanthin esters; occasionally low levels of -carotene were detected in the digestive gland. The concentrations of astaxanthin monoesters (AM) and diesters (AD) were highest, with only minor amounts of free astaxanthins (Ast), except in the maturing ovaries, where free astaxanthins predominated (up to 80% of the total carotenoid). Of the total carotenoid, 82 to 94% was in the integument, but at maturity the digestive gland contained 10.7±3.4% and the ovary 5.6±0.9% of the total carotenoid. Only the ovary increased in mass during maturation, reaching up to 5.2% of total prawn mass. During this period, digestive gland concentrations of AM, AD and Ast all increased (tota 20 to 120 g g^-1); levels in the muscle and integument varied little throughout maturation (total 0.4 and 100 g g^-1, respectively); ovary AM levels remained low throughout (1.5 to 1.2 g g^-1), AD increased from only 2 to 5 g g^-1, but Ast increased from 2 to 34 g g^-1. Apart from the ovary, AM concentrations were the most variable. In common with other decapod Crustacea, the maturing ovary of P. esculentus contained high levels of carotenoids, indicating that these may have an important role in early development. The natural diet of P. esculentus includes a variety of carotenoids, but except for a little -carotene, the digestive gland, where absorption occurs, contained astaxanthins, with only an occasional trace of -carotene. This suggests that the conversion of dietary carotenoids to astaxanthin occurs soon after ingestion.     

Natural diet of larval Penaeus merguiensis (Decapoda: Penaeidae) and its effect on survival

The relationship between Penaeus merguiensis protozoea larvae and their phytoplankton diet was examined using seasonal plankton surveys and in situ rearing experiments. Larval abundance, phytoplankton community structure, and chlorophyll a concentration in Albatross Bay, Gulf of Carpentaria, were monitored monthly for 2 yr. Larval abundance peaked in November (spring) and March (autumn), at which times diatoms were the most abundant group in net samples of phytoplankton and in the guts of larvae. During November 1989 and March 1990, larvae were reared in nylon mesh enclosures positioned throughout the water column at three depths: 0 to 3 m, 3 to 6 m and 6 to 9 m. Overall, larval survival and gut fullness were both higher in November than in March. In both months, larval survival was lower at the surface than at other depths. This correlated with lower chlorophyll a concentrations, but lower total cell densities were not detected. During the in situ experiments, diatoms were the most abundant phytoplankton group in the water column and in the guts of larvae and, therefore, appeared to be the principal diet of larvae. Pigment analysis demonstrated that while gut contents generally reflected the composition of the phytoplankton community, the larvae were not feeding exclusively on diatoms. They also ingested green algae and possibly seagrass detritus. The in situ experiments demonstrated that the predominantly diatom flora in Albatross Bay can provide a nutritionally adequate environment for prawn larvae even at seasonally low levels. It is unlikely, therefore, that starvation is a major cause of mortality of P. merguiensis larvae during either of the biannual peaks in their abundance in Albatross Bay, Gulf of Carpentaria.     

Variation in lipid classes during the molting cycle of the prawn Penaeus japonicus

The variation in the concentration and fatty acid composition of lipid classes during the molting cycle of the prawn Penaeus japonicus was investigated. The lipid concentration of the whole body reached a maximum at mid-premolt (Stage D₂) and then decreased to low level at late premolt (Stage D_3–4). The accumulation of lipids during the premolt period seemed to be attributable to the increase of both polar and neutral lipids. The increase of neutral lipids at Stage D₂ was derived from not only triglycerides but also free sterols and free fatty acids. Regarding the fatty acid composition of every lipid class, a marked variation occurred mainly at the intermolt (Stage C). In this stage, the polar lipids were rich in monoenoic acids such as 18:1 and poor in polyenoic acids such as 20:53 and 22:63. The triglycerides were rich in polyenoic acids at Stage C, but poor in monoenoic acids such as 16:1 and 18:1. The steryl esters contained large amounts of saturated acids such as 16:0 and 18:0 throughout the molting cycle, however the level of polyenoic acids increased at Stage C.     

Rearing of prawn larvae,Penaeus japonicus,fed soy-cake particles and diatoms

Soy cake^* was homogenized and filtered through an 80 mesh net to produce small, detritus-like particles. The effect of soy-cake particles, an artificial detritus, on the survival and growth of Penaeus japonicus Bate zoea was then tested. The soy cake was considered to be effective for survival and growth of the zoea. The best survival rate, 85.9%, was obtained in a tank receiving soy cake in quantities of 0.16 mg/zoea/day. An experiment was also performed to compare three kinds of food: particles of soy cake alone, diatoms (Chaetoceros rigidus) alone, and a half and half mixture of the two. The best growth, 2.49 mm, and the highest survival rate, 79.1%, were found in larvae fed the mixture of soy-cake particles and diatoms. The results thus seem to demonstrate that particles of soy cake could be usefully applied to the mass-culture of the penaeid prawn.     

Effect of salinity on hemolymph calcium concentration during the molt cycle of the prawn Penaeus monodon

Prawns (Penaeus monodon) were obtained from ponds in Iloilo, Philippines, in 1984 and 1985 and maintained in salinities from 8 to 44. Total hemolymph calcium was largely affected by molt stage and less so by salinity. A sharp, transient increase in hemolymph calcium occurred 3 to 6 h postmolt, followed by an equally rapid decrease from 6 h postmolt to intermolt. This biphasis response was limited to prawns in 8, 20 and 32S; in 44S, hemolymph calcium remained the same throughout the sampling period. Peak concentrations of total calcium were greater in low (8 and 20S) than in high salinities. Salinity had no effect on the duration of molt cycle nor on time of occurrence of molt. Almost half of molting incidents occurred between 18.01 and 0.00 hrs, and one-third between 0.01 and 06.00 hrs.     

Route of egg yolk protein uptake in the oocytes of kuruma prawn,Penaeus japonicus

The route of egg yolk protein uptake into the oocytes of kuruma prawn, Penaeus japonicus, was studied using immunohistochemical and electron microscopical methods. Although a significant immunofluorescence with anti-vitellin-immunoglobulin was observed in the enlarged follicle cells surrounding oil globule stage oocytes of the early vitellogenic ovary, no fluorescence was detected in shrunken follicle cells surrounding oocytes in the yolk granule stage. Electron microscopically, yolk granule stage oocytes have an irregular surface with numerous well-developed microvilli. In contrast, the surface of follicle cells is relatively smooth. The irregular surface of yolk granule stage oocytes was covered with a layer of electron dense material. Similar dense material was found in the spaces between the neighboring follicle cells on the yolk granule stage oocytes. The outer surface of the follicle cells on yolk granule stage oocytes was covered by dense materials which were similar to those found on the irregular surface of oocytes. Micropinocytotic vesicles containing dense material were found in the ooplasm near the irregular surface with numerous well-developed microvilli. Dense material was concentrated in the peripheral part of the small forming yolk bodies of yolk granule stage oocytes. This suggests that the electron dense material, probably egg yolk protein, transferred to the surface of yolk granule stage oocytes from the spaces between the neighboring follicle cells may be incorporated into the ooplasm by pinocytosis through the microvilli and subsequently aggregate to form yolk bodies.     

Influence of salinity and temperature on the oxygen consumption in young juveniles of the Indian prawn Penaeus indicus

Routine oxygen consumption of very young juveniles (0.1 g) of Penaeus indicus H. Milne Edwards was significantly influenced by ambient temperature and weight of the animal, but not by ambient salinity, when tested at salinities (7, 21, and 35) to which they had been long-term (over 10 days) acclimated. Standard oxygen consumption of young juvenile prawns (1 to 3 g), subjected to step-wise changes in ambient salinity, from sea water to low salinity waters (2 to 6), and measured after short-term (24 h) salinity acclimation at each step, was lowest at salinities where prawns such as those tested occur naturally (10 to 15). The metabolic rates do not appear to have a direct relation to the osmotic gradient, even when the influence of interfering activity is eliminated. It appears that factors other than osmotic gradient will have to be sought in order to explain the metabolic patterns of P. indicus in relation to salinity.     

The Influence of Temperature and Salinity Upon the Acute Toxicity of Heavy Metals to the Banana Prawn (Penaeus merguiensis de Man)

Bioassays were conducted to determine the effects of temperature and salinity on the acute toxicity of mercury, copper, cadmium, zinc, nickel and lead to juvenile banana prawns (Penaeus merguiensis de Man). Tests were conducted at all combinations of 35, 30 and 20°C with 36 and 20° salinity over 96 h. The general rank order of metal toxicity was Hg > (Cu, Cd, Zn) > Ni > Pb. The toxicity of all metals increased with increased temperature. This was most noticeable in the high salinity treatments, particularly for copper and zinc. Salinity appeared to influence the toxicity of all metals tested although significant differences were only found for copper and lead at 20°C. At this temperature prawns were markedly more susceptible to both metals in low salinity sea water. The data are compared with lethal concentrations found for other crustaceans and are discussed in relation to existing water quality criteria.     

Changes in protein-bound and free amino acids in the muscle of the tiger prawn Penaeus esculentus during starvation

Using the starvation technique, changes in protein and free amino acids were examined in Penaeus esculentus Haswell collected from Moreton Bay, Australia, by trawling in 1985. Prawns of 17.7±0.26 g wet weight were held at 25°C until 2 d after moulting. Groups of seven or eight were then starved fro 5, 10, or 15 d, with appropriate control groups. At the end of each period, ecreted amino acids were collected for 24 h and whole-muscle amino acids and free amino acids (FAA) g^-1 in each prawn were analysed. Concentrations of whole-muscle amino acids showed only minor changes with starvation, but concentrations of many of the FAA changed significantly. Total FAA averaged 1 182±45 mol g^-1 dry weight. Individual FAA, in order of abundance, were glycine, arginine, proline, taurine, threonine, hydroxyproline, alanine, glutamic acid, valine, aspartic acid and lysine; the remaining FAA each contributed <0.2% of the total. Only taurine and alanine did not show significant changes with starvation. Concentrations of glycine, arginine, hydroxyproline, glutamic and aspartic acid increased, while those of proline, threonine, valine and lysine decreased with starvation, that of proline approaching zero after 15 d starvation. Excreted amino acid-nitrogen represented <2% of excreted ammonianitrogen ornithine being the most abundant (35%), followed by leucine (22%) and lysine (17%). The relative abundance of excreted amino acids did not correspond with those of the FAA. It is suggested that, as starvation progresses, the muscle protein is progressively hydrolysed, but with the remaining muscle maintaining its amino acid composition. The liberated amino acids enter the FAA pool and become available for energy production. Proline may have an important role as an energy source, but the ability to synthesise proline may be limited, and thus the artificial food of penaeid prawns may be improved by its addition.     

Osmotic and chloride regulation in the hemolymph of the tiger prawn Penaeus monodon during molting in various salinities

The effect of molting on osmotic and chloride concentrations in the blood of the prawn Penaeus monodon Fabricius (20±3 g) at various salinities was investigated. Prawns were obtained from ponds in Iloilo, Philippines, in 1984. They were stocked in salinities of 8, 20, 32 and 44, and their hemolymph was sampled during molt (Time 0), and then 0.125, 0.25, 0.5, 1, 2, 4, 6, 10 and 14 d after molting. Prawns during and immediately after molt tended to conform to the environmental osmolality. Subsequent postmolt (0.5 d) stages displayed more divergence from external salinity. The isosmotic point was higher (940±30 mOsm kg^-1) during molt than during intermolt (663±8 mOsm/kg^-1), suggesting different osmotic requirements in early molt. Hyperregulation of hemolymph chloride below 20 S, as well as isoionic point (301±6 mM), were independent of molting stage. At 20 S and above, newly molted (0 to 0.25 d post-molt) individuals tended to conform to the external chloride concentration while intermolt (0.5 d) post-molt individuals did not. Contribution of hemolymph chloride to hemolymph osmolality was greater during intermolt than during ecdysis, suggesting an important role for other negatively charged ions during molt. When molt occurred in 20 S (the test salinity most similar to the isoionic salinity), there was little or no change in hemolymph osmolality or chloride concentration from 0 to 14 d postmolt. At 8, 32 and 44 S, the change from molt to intermolt values in hemolymph osmotic and chloride concentrations was hyperbolic. Non-linear least-squares regression showed that prawns generally achieved intermolt values within 1 d after molting. Prawns at intermolt regulated hemolymph osmolality (620 to 820 mOsm kg^-1) and chloride concentration (300 to 450 mM) at a much narrower range than during molt (520 to 1 170 mOsm kg^-1 and 250 to 520 mM, respectively). Hemolymph osmolality was a more sensitive indicator of physiological response than hemolymph chloride concentration. Distribution and culture of P. monodon might be limited in low salinities by its ability to maintain a hemolymph osmolality 500 mOsm kg^-1 during molt and 600 mOsm kg^-1 in intermolt, and in high salinities by its capacity to reduce the hemolymph osmolality from values at molt to those in intermolt. Osmotic and chloride concentrations in the blood of P. monodon clearly varied with both molt stage and salinity of the medium. Dependence on external factors, however, gradually declined in older molt stages, suggesting a reduction in integument permeability and greater development of ion absorption/secretion mechanisms as the exoskeleton hardened.SEAFDEC Contribution No. 197     

Population genetic structure of the brown tiger prawn, Penaeus esculentus, in tropical northern Australia

Eight polymorphic microsatellite loci were analysed in six population samples from four locations of the Australian endemic brown tiger prawn, Penaeus esculentus. Tests of Hardy–Weinberg equilibrium were generally in accord with expectations, with only one locus, in two samples, showing significant deviations. Three samples were taken in different years from the Exmouth Gulf. These showed no significant heterogeneity, and it was concluded that they were from a single panmictic population. A sample from Shark Bay, also on the west coast of Australia, showed barely detectable differentiation from Exmouth Gulf (F _ST = 0 to 0.0014). A northeast sample from the Gulf of Carpentaria showed low (F _ST = 0.008) but significant differentiation from Moreton Bay, on the east coast. However, Exmouth Gulf/Shark Bay samples were well differentiated from the Gulf of Carpentaria/Moreton Bay (F _ST = 0.047–0.063). The data do not fit a simple isolation by distance model. It is postulated that the east–west differentiation largely reflects the isolation of east and west coast populations that occurred at the last glacial maximum when there was a land bridge between north-eastern Australia and New Guinea.     

Fatty acid composition of organs and tissues of the tiger prawn Penaeus esculentus during the moulting cycle and during starvation

The fatty acids (FA) in neutral lipid (NL) and polar lipid (PL) of digestive gland, muscle and integument of Penaeus esculentus Haswell were analysed and compared during the moulting cycle and during starvation. The prawns were collected from Moreton Bay, Queensland, Australia, by trawling during 1985–1987, and were fed with a standard semi-purified diet. Compared with a natural diet, the artificial diet had much higher levels of 18:1n-9 and 18:2n-6, but only trace amounts of 20:4n-6, but there was no evidence of dietary imbalance. The fatty acid composition (percentage of total lipid) of the digestive gland changed markedly during the moulting cycle and during starvation, but the small changes observed in both muscle and integument suggested that these tissues maintained their composition under both conditions. When the fatty acids were calculated as absolute amounts, muscle composition, as well as that of the digestive gland, changed significantly. In the digestive gland, saturated FA (SFA), monounsaturated FA (MUFA), diunsaturated FA (DUFA) and polyunsaturated FA (PUFA) all increased up to the middle of the moulting cycle and then declined; with starvation all groups decreased. In muscle, SFA, MUFA and DUFA all increased during the moulting cycle; starvation caused SFA, MUFA and PUFA to decrease, whereas DUFA did not vary. Starvation caused both 18:2n-6 (linoleic) and 18:3n-3 (linolenic) in the digestive gland to reach or almost reach zero. The other essential PUFA, 20:4n-6 (arachidonic), 20:5n-3 (eicosapentaenoic) and 22:6n-3 (docosahexaenoic), decreased during the moulting cycle, but during starvation 20:4n-6 did not decrease as much. In muscle, the levels of 18:2n-6 and 18:3n-3 increased, while 20:4n-6, 20:5n-3 and 22:6n-3 remained approximately constant during the moulting cycle. Starvation reduced 20:5n-3 and 22:6n-3 to about 60%. The data suggest that levels of 18:3n-3, 20:4n-6, 20:5n-3 and 22:6n-3 are regulated, and that 20:4n-6 can be synthesised from 18:2n-6. There is no clear evidence that 20:5n-3 and 22:6n-3 are essential in P. esculentus, but tissue catabolism of cell membranes during starvation may have provided sufficient amounts for maintenance.