Life history of Amitus fuscipennis (Hym., Platygastridae) as parasitoid of the greenhouse whitefly Trialeurodes vaporariorum (Hom., Aleyrodidae) on tomato as function of temperature

Life history parameters of Amitus fuscipennis MacGown and Nebeker as parasitoid of Trialeurodes vaporariorum (Westwood) were determined at 15, 20, 25 and 30°C on tomato using three different methods. For each method, immature development, mortality, longevity, fecundity, oviposition frequency and post-oviposition period were determined and temperature-dependent relations were estimated. Oviposition frequency was also estimated as a function of parasitoid age. Immature development had a maximum of 61 days at 15°C that decreased to 22 days at 30°C. Mortality in the grey stage was less than 2% at temperatures lower than 30°C, where it was 60%. Longevity fluctuated between 3 and 18 days. Fecundity increased from 338 eggs/female at 15°C to a maximum of 430 eggs/female at 25°C and then decreased to 119 eggs/female at 30°C. Oviposition frequency varied between 3 and 46 eggs/female per day and had its maximum on the first day after emergence of the parasitoid. Net reproduction rate, generation time and intrinsic rate of increase were calculated. The intrinsic rate of increase increased from 0.090 at 15°C to a maximum of 0.233 at 25°C and then decreased to 0.159 at 30°C. The influence of the methods to determine the life history parameters on the results is discussed. The results are compared also with the life history of Encarsia formosa Gahan (Hym., Aphelinidae) a parasitoid of the same host. The advantages and disadvantages of the pro-ovigenic A. fuscipennis in comparison with the synovigenic E. formosa are discussed.     

Effects of development, temperature and salinity on metabolism in eggs and yolk-sac larvae of milkfish, Chanos chanos (Forsskål)

Oxygen uptake rates and yolk-inclusive dry weiGhts were measured during the egg and yolk-sac larval stages of milkfish, Chanos chanos (Forsskal). Oxygen uptake by eggs and yolk-sac larvae was measured to assess the effects of four salinities (20,25,30,35 ppt) at 28°C. The effects of three temperatures (23,28,33°C) on oxygen uptake by yolk-sac larvae were determined at a salinity of 35 ppt. Dry weights were measured throughout embryonic development at 28°C and the yolk-sac stage at 23.28 and 33°C.
Oxygen uptake rates of eggs increased more than fivefold during embryogenesis (0.07±0.03 to 0.40 ± 03 μl O₂ egg ⁻¹ h ⁻¹;blastula to prehatch stage). Larval oxygen uptake did not change with age but was affected by rearing temperature (0.33 ± 0.08, 0.44 ± 0.07 and 0.63 ± 0.13 μl O₂ larva ⁻¹ h⁻¹ at 23, 28 and 33°C, respectively; Q₁₀= 1.93). Acute temperature changes from 28 to 33°C caused significant increases in oxygen uptake by embryos (Q ₁₀= 1.69–3.58) and yolk-sac larvae (Q ₁₀=2.55). Salinity did not affect metabolic rates.
Dry weight of eggs incubated at 28°C decreased 13% from fertilization to hatching. Incubation temperatures from 23–33°C did not affect dry weights at hatching. Rearing temperatures significantly affected the rate of larval yolk absorption (Q ₁₀= 2.25).     

Life table and biological studies of Harmonia axyridis Pallas (Col., Coccinellidae) reared on the grain moth eggs of Sitotroga cerealella Olivier (Lep., Gelechiidae)

The developmental period of immature stages, survival per cent, longevity, fecundity and life table parameters of Harmonia axyridis by feeding on fresh and frozen grain moth eggs (GME) of Sitotroga cerealella were studied under laboratory conditions. The effect of crowding adults on fecundity of females was also determined. The total developmental time from egg hatching to adult eclosion ranged from 18.89 ± 0.32 to 22.5 ± 0.21 days on fresh and frozen GME, respectively. Survival per cent from egg hatching to adult emergence differed significantly when the predator fed on the two diets of GME. Also, pupal and adult weights were affected by feeding on fresh and frozen GME. There were no significant differences in longevity of females, while there were significant variations in fecundity of females and longevity of males. The calculated values of T , DT , R_o , r_m , and e^rm were high by feeding on fresh GME. Morever, rates of survivorship ( Lx ), and maximum oviposition per female per day ( Mx ) were higher when the predator was reared on fresh than on frozen GME. Crowding conditions of predator adults affected the fecundity of females due to egg cannibalism by both males and females of the predator.     

Plant palatability and disturbance level in aquatic habitats: an experimental approach using the snail Lymnaea stagnalis (L.)

1. The palatability of aquatic macrophytes to the snail Lymnaea stagnalis was investigated in the laboratory. Eight species of macrophyte were selected from habitats that differed in either flood disturbance regime or nutrient status.
2. In a non-choice test, single macrophyte species were offered to individual snails. The average amount of plant dry mass consumed per Lymnaea dry mass ranged from 3.6 ± 1.4 (±SE) to 63.6 ± 13.9 mg g^–1 day^–1 across plant species. In a choice test, all eight plant species were presented simultaneously to sets of five snails. The average total consumption was 66.1 ± 3.8 mg g^–1 day^–1 and the maximum average consumption for a single plant was 26.2 ± 3.6 mg g^–1 day^–1.
3. In both tests, the amount consumed by snails differed significantly between the plant species. The species growing in undisturbed habitats were the least consumed. Habitat nutrient status was unrelated to plant palatability.
4. These results suggest that macrophyte species growing in habitats that are rarely disturbed by floods allocate a greater proportion of their resources to resisting herbivory.     

Life history traits of Aphis gossypii Glover (Hom., Aphididae) reared on four widely distributed weeds

Variation in the life history traits of cotton aphids, Aphis gossypii Glover, reared on four widely distributed weeds, Ageratum houstonianum Mill., Bidens pilosa L. var. radiata Sch. Bip., Solanum nigrum L. and Spermacoce latifolia Aubl., were investigated. Cotton aphids were reared in the laboratory at 25°C. Each host plant had a distinct effect on aphid life history traits. Cotton aphids reared on S. nigrum had a significantly shorter developmental period, and age-specific fecundity peaked early. In contrast, cotton aphids reared on S. latifolia had a long developmental period and low age-specific fecundity. Cotton aphids that fed on B. pilosa and A. houstonianum displayed intermediate rates of growth and age-specific fecundity. Because the curves of age-specific fecundity ( m_x ) and age-specific net maternity ( l_x  m _x ) on each host plant were close together, development time and the pattern of age-specific fecundity were the major factors determining the population growth potential of the cotton aphid on each weed. As a result, the intrinsic rate of population growth for aphids reared on S. nigrum was significantly higher ( r_m =0.527 ± 0.011) than it was for aphids reared on S. latifolia ( r_m =0.194 ± 0.012).     

Seasonal patterns of nitrogen fixation in termites

1. Termite nitrogenase activity was highest in autumn and spring (≈ 3 μg N₂ fixed termite fresh mass (g)^–1 day^–1) and lowest in winter and summer (≈ 0·8 μg N₂ fixed termite fresh mass (g)^–1 day^–1).
2. The nitrogenase activity of worker termites was significantly higher than all other castes (1·58 ± 0·27 μg N₂ fixed termite fresh mass (g)^–1 day^–1).
3. Worker termites constituted the largest proportion of all the castes throughout the study period (≈ 90%).
4. The localized input of fixed nitrogen by termites may reach 15·3 mg N log^–1 day^–1 and 5·6 g N log^–1 year^–1.     

Long-term effects of successive Ca(OH)2 and CaCO3 treatments on the water quality of two eutrophic hardwater lakes

1. Whole-lake experiments were conducted in two hardwater lakes (Halfmoon and Figure Eight) in Alberta, Canada, to investigate the effectiveness of repeated lime (slaked lime: Ca(OH)₂ and/or calcite: CaCO₃) treatments (5–78 mg L^–1) for up to 7 years.
2. Randomized intervention analysis of intersystem differences between the experimental and three reference lakes demonstrated a decline in euphotic total phosphorus and chlorophyll a concentrations in the experimental lakes after repeated lime treatments.
3. After the second lime application to Halfmoon Lake, mean winter total phosphorus release rates (TPRR) decreased to < 1 mg m^–2 day^–1 compared with 3.6 mg m^–2 day^–1 during the winter after initial treatment. In the final year of lime application, mean summer TPRR decreased to 4.5 mg m^–2 day^–1 compared with 7.6 mg m^–2 day^–1 in the pre-treatment year.
4. Mean macrophyte biomass declined and species composition was altered at 1 and 2 m depths in Figure Eight Lake during lime application. Over the first 6 years of treatment, macrophyte biomass at 2 m declined by 95% compared with concentrations recorded during the initial treatment year. In the last year of the study, macrophyte biomass at 2 m reached initial treatment concentrations, which coincided with the greatest water transparency. Over the treatment period, macrophyte species shifted from floating to rooted plants.
5. Multiple lime applications can improve water quality in eutrophic hardwater lakes for periods of up to 7 years.     

Searching and oviposition behaviour of Amitus fuscipennis, a parasitoid of the greenhouse whitefly

Abstract: Amitus fuscipennis MacGown & Nebeker (Hym., Platygasteridae) is a parasitoid of the greenhouse whitefly, Trialeurodes vaporariorum (Westwood) (Hom., Aleyrodidae) on some crops as bean and snap bean (both Phaseolus vulgaris L.) in Colombia. The searching and oviposition behaviour of A. fuscipennis was studied in the laboratory, using T. vaporariorum as a host on bean leaves. The parasitoid's basic search pathway consisted of walking, encountering the host, and drumming and probing it. While walking, the parasitoid stopped for short periods of time, partly to preen itself. Walking while searching comprised 61% of the adults' time budget and probing hosts represented 16%. After a host nymph was parasitized by A. fuscipennis , the parasitoid remained close by and continued searching for new hosts in the immediate vicinity. Such behaviour suggests area-restricted searching. The parasitoid preferred first instars of T. vaporariorum for oviposition, resulting in long developmental times. Amitus fuscipennis had a high percentage of host acceptance resulting in a high percentage parasitism (60%) of all encountered hosts. Amitus fuscipennis , on average, walked faster before an oviposition (1.4 mm/s) than other whitefly parasitoids. The implications of these findings for the control of T. vaporariorum are discussed.     

Influence of temperature on life-table parameters of Stethorus gilvifrons (Mulsant) (Coleoptera: Coccinellidae) fed on Tetranychus urticae Koch

The influence of temperature on life-table parameters, fecundity and survivorship of the predatory ladybird, Stethorus gilvifrons , fed on Tetranychus urticae was determined at seven constant temperatures of 15°C, 20°C, 25°C, 28°C, 30°C, 35°C and 40°C. No development was observed at 40°C, thus being regarded as the threshold for the development of S. gilvifrons . The results indicate a significant decrease in male and female longevity with increasing temperature from 15°C to 35°C. The longest and shortest longevity were 18.40 and 12.75 days for males and 17.40 and 8.80 days for females, respectively. The intrinsic rate of natural increase ( r _m ) and the net reproductive rate ( R ₀) of S. gilvifrons linearly increased with increasing temperatures from 15°C to 35°C, while the mean generation time ( T ) and doubling time (DT) decreased linearly within this temperature range. The highest values of r _m (0.240 females/female/day) and R ₀ (59.27 females/female) and the lowest mean generation time (17.01 days) and DT (2.88 days) were recorded at 35°C. The maximum (185.50 eggs) and minimum (25.50 eggs) measurement of total fecundity was also recorded at 35°C and 15°C, respectively. The results indicate that temperature greatly affected fecundity, survivorship and life-table parameters of S. gilvifrons , and that 35°C is a suitable temperature for population growth of this predator.     

Demographic parameters of cotton aphid, Aphis gossypii Glover （Homoptera： Aphididae） on five cotton cultivars

Life table parameters of the cotton aphid, Aphis gossypii Glover, were estimated on five cotton cultivars （‘ Sealand＇ ,‘Siokra＇ ,＇ Vararnin＇ ,‘ Bakhtegan＇ and ‘ Sahel＇ ）. Demographic parameters of the cotton aphid were assessed at 27.5 ± 1 ℃, 65% ＋ 10% RH and a photoperiod of 14：10 （L： D）h. The shortest developmental time for the nymphal stages was 5.5 days on ‘Siokra＇ and the longest was 6.1 days on‘ Sealand＇. The highest offspring per female was 29.6 on ‘Sahel＇ and the lowest was 15.3 on ‘Sealand＇. The rm values varied from 0.272 on ‘Sealand＇ to 0.382 （day^-1） on ‘Varamin＇. Jackknife estimates of the A. gossypii parameters on these cultivars indicated the greatest developmental rate and fecundity on ‘ Varamin＇ and the poorest on ‘ Sealand＇ cultivar.     

Development and reproduction of Bemisia tabaci （Homoptera： Aleyrodidae） on three bean species

Abstract The development, survivorship and reproduction of Bemisia tabaci B-biotype on three bean species were studied at 26±1°C in the laboratory. The developmental periods from egg to adult varied from 27.80 days on garden beans to 18.20 days on soybeans. The survivorship from egg to adult on soybeans, cowpeas and garden beans was 77.14, 70.14 and 64.28%, respectively. The average longevity of female adults ranged from 12.30 days on soybeans to 9.80 days on garden beans, and the oviposition of B. tabaci varied from 160.85 eggs on soybeans to 98.00 eggs on garden beans. Life table parameters were calculated as biological attributes for Bemisia tabaci populations fed on three bean species. The results indicated that the intrinsic rate of increase (r_m), the finite rate of increase (λ) and net reproductive rate (R₀) were high for populations fed on soybeans, with values of 0.1857, 1.2041 and 82.1576, respectively. The corresponding values were less for populations fed on garden beans, with values of 0.1097, 1.1159 and 31.2661, respectively. The parametric values for cowpeas were intermediate between soybeans and garden beans but no significant difference were observed for the r_m values for soybeans and cowpeas. Experimental evidence in our investigation indicated that Bemisia tabaci is best adapted and shows the greatest preference for soybean of the three bean species tested in this study.     

Oxygen consumption of East Siberian cod: no support for the metabolic cold adaptation theory

Standard metabolic rate ( R _s) at 2°C of eight East Siberian cod Arctogadus borisovi , caught in West Greenland, body mass of 601.5 ± 147.6 g (mean ± s.D.), was 40.9 ± 5.9 mg O₂ kg^-1 h^-1 and 59.0 ± 6.6mg O₂ kg^-1 h^-1 when extrapolated to a standardized 100 g fish. R _s was compared with three other Gadidae, to test the theory of metabolic cold adaptation (MCA). There was no evidence of MCA in the family.     

Effect of long-term and rapid cold hardening on the cold torpor temperature of an aphid

Abstract.  The effect of long-term (seasonal) acclimation and rapid cold hardening is investigated on the cold torpor temperature ( CT _min) of adult grain aphids, Sitobion avenae, reared at 20 or 10 °C for more than 6 months before experimentation. Rapid cold hardening is induced by exposing aphids reared at 20 to 0 °C for 3 h and aphids reared at 10 to 0 °C for 30 min (acclimation regimes previously found to induce maximum rapid cold hardening). The effect of cooling aphids from the same rearing regimes from 10 to −10 °C at 1, 0.5 and 0.1 °C min⁻¹ is also investigated. In the 20 °C acclimated population, rapid cold hardening and cooling at 0.1 °C min⁻¹ both produce a significant decrease in CT _min from 1.5 ± 0.3 to –0.9 ± 0.3 and –1.3 ± 0.3 °C, respectively. Rapid cold hardening also results in a significant reduction in CT _min of the population reared at 10 °C from 0.8 ± 0.1 to –0.9 ± 0.2 °C. However, none of the cooling regimes tested reduces the CT _min of the winter-acclimated (10 °C) population. The present study demonstrates that rapid cold-hardening induced during the cooling phase of natural diurnal temperature cycles could lower the movement threshold of S. avenae , allowing insects to move and continue feeding at lower temperatures than would otherwise be possible.     

Purification and biochemical characterization of a membrane-bound [NiFe]-hydrogenase from a hydrogen-oxidizing, lithotrophic bacterium, Hydrogenophaga sp. AH-24

Membrane-bound [NiFe]-hydrogenase from Hydrogenophaga sp. AH-24 was purified to homogeneity. The molecular weight was estimated as 100±10 kDa, consisting of two different subunits (62 and 37 kDa). The optimal pH values for H₂ oxidation and evolution were 8.0 and 4.0, respectively, and the activity ratio (H₂ oxidation/H₂ evolution) was 1.61 × 10² at pH 7.0. The optimal temperature was 75 °C. The enzyme was quite stable under air atmosphere (the half-life of activity was c . 48 h at 4 °C), which should be important to function in the aerobic habitat of the strain. The enzyme showed high thermal stability under anaerobic conditions, which retained full activity for over 5 h at 50 °C. The activity increased up to 2.5-fold during incubation at 50 °C under H₂. Using methylene blue as an electron acceptor, the kinetic constants of the purified membrane-bound homogenase (MBH) were V _max=336 U mg⁻¹, k _cat=560 s⁻¹, and k _cat/ K _m=2.24 × 10⁷ M⁻¹ s⁻¹. The MBH exhibited prominent electron paramagnetic resonance signals originating from [3Fe–4S]⁺ and [4Fe–4S]⁺ clusters. On the other hand, signals originating from Ni of the active center were very weak, as observed in other oxygen-stable hydrogenases from aerobic H₂-oxidizing bacteria. This is the first report of catalytic and biochemical characterization of the respiratory MBH from Hydrogenophaga .     

Food intake and growth in the Moses perch, Lutjanus russelli (Bleeker), with reference to predation on penaeid prawns

Juvenile Moses perch were fed various rations of penaeid prawn and pilchard foods at 26.4 and 28.7° C to elucidate feeding–growth relationships. Maintenance rations amounted to 5.0 and 3.8% of body weight per day (BW day^–1) on prawn and pilchard diets, respectively, at 26.4° C and 4.5% BW day ¹ for prawn at 28.7° C. This apparent reduction in maintenance ration at higher temperature is probably due to reduction in activity levels. Starvation weight loss, an indicator of resting metabolic rate, increased with temperature and exhibited a Q¹⁰ of 2.0 to 2.4.
Fish fed ad libitum once or twice per day at 26.4° C grew at 1.1 % BW day^–1 and ingested about 9% of their BW day^–1. At 28.7° C fish ingested about 8% of their BW day^–1 and grew 1 .0% BW day^–1. These growth rates are comparable to those of similar sized lutjanids in the wild. Since prawns comprise 64% of the diet of Moses perch in northern Australia, this level of consumption would require about 6% BW day^–1 of prawns. The relevance of these findings to the assessment of predator impact on prawns in Australian estuaries is discussed.     

Growth, diet and metabolism of common wolf–fish in the North Sea, a fast–growing population

The von Bertalanffy growth parameters for common wolf–fish Anarhichas lupus in the North Sea were: male: L ∞=111·2 cm, t ₀=–0·43 and K =0·12; and female: L ∞=115·1 cm, t ₀=–0·39 and K =0·11, making this the fastest growing stock reported. Resting metabolic rates (RMR±S.E.) and maximum metabolic rates (MMR±S.E.) for six adult common wolf–fish (mean weight, 1·39 kg) at 5° C were 12·18±1·6 mg O₂ kg^–1 h^–1 and 70·65±7·63 mg O₂ kg^–1 h^–1 respectively, and at 10° C were 25·43±1·31 mg O₂ kg^–1 h^–1 and 113·84±16·26 mg O₂ kg^–1 h^–1. Absolute metabolic scope was 53% greater at 10° C than at 5° C. The diet was dominated by Decapoda (39% overall by relative occurrence), Bivalvia (20%) and Gastropoda (12%). Sea urchins, typically of low energy value, occupied only 7% of the diet. The fast growth probably resulted from summer temperatures approximating to the optimum for food processing and growth, but may have been influenced by diet, and reduced competition following high fishing intensity.     

Sequence of gonadal events and oestradiol levels in Sparus aurata (L.) under two photoperiod regimes

Individually tagged Sparus aurata were kept in tanks with running sea water (21°± 2°C) during their second and third years of life. Gonads were biopsied and blood was sampled at monthly intervals. Thirteen of 50 fish in the second year and 24 of 35 fish in the third year were phenotypically females. Fish kept under 16L/8D photoperiod from July 1981 to August 1982 did not reach maturation; waves of initial ovarian growth alternated with waves of atresia. When photoperiod was shortened as from August 1982, gonadal development commenced within a month and proceeded at a rate higher than that of the control fish reared under natural photoperiod. Under natural photoperiod oestradiol serum levels (E₂) were relatively low during the resting phase, May-October (108 ± 11 pg ml⁻¹), and during the late vitellogenic phase (502 ± 76 pg ml⁻¹). High levels (1669 ± 312 and 1240 ± 172pg ml⁻¹) occurred during the early vitellogenic and the maturational phases. The high level of E₂ during the spawning season of S. aurata is explained by earlier reports indicating a prolonged breeding season with daily release of eggs, and alternating daily surges of E₂ and 17α, 20β, dihydroxy-4-pregnen-3-one, possibly a 'maturational progestin' in this fish. In phenotypic males, E₂ was highest during early spermatogenic phases (745 ± 142pg ml⁻¹) but was low (155 ± 11 pg ml⁻¹) in males with running sperm.     

Effects of temperature, body size and feeding on rates of metabolism in young‐of‐the‐year haddock

The mean rate of oxygen consumption (routine respiration rate, R _R, mg O₂ fish⁻¹ h⁻¹), measured for individual or small groups of haddock Melanogrammus aeglefinus (3–12 cm standard length, L _S) maintained for 5 days within flow‐through respiratory chambers at four different temperatures, increased with increasing dry mass ( M _D). The relationship between R _R and M _D was allometric ( R _R = α  M ^b ) with b values of 0·631, 0·606, 0·655 and 0·650 at 5·0, 8·0, 12·0 and 15·0° C, respectively. The effect of temperature ( T ) and M _D on mean R _R was described by     indicating a Q ₁₀ of 2·27 between 5 and 15° C. Juvenile haddock routine metabolic scope, calculated as the ratio of the mean of highest and lowest deciles of R _R measured in each chamber, significantly decreased with temperature such that the routine scope at 15° C was half that at 5° C. The cost of feeding ( R _SDA) was c . 3% of consumed food energy, a value half that found for larger gadoid juveniles and adults.     

Geographical variation in egg cold hardiness: a study on the adaptation strategies of the migratory locust Locusta migratoria L.

Abstract. 1. For many species of insect, cold hardiness is an important trait that enables a population to develop in the next season and to extend its range. To elucidate the role of cold hardiness of the migratory locust Locusta migratoria L. in its outbreak and distribution areas, egg cold hardiness was examined in locusts derived from four locations from latitude 18°23'N to latitude 41°10'N in eastern China.
2. The supercooling points of eggs from different geographic populations did not differ significantly for the first development stage, with an average ± SE of −24.5 ± 0.51 °C, or for the second stage, −22.06 ± 0.68 °C, however there was a significant difference for the embryonic development phase among the four geographical populations. The egg supercooling point increased gradually from neonatal egg to old egg; eggs prior to hatching always had a much higher supercooling point.
3. Comparisons of the cold hardiness of four populations were carried out by validating the close correlation between latitude and the effects of cold on hatching, low lethal temperature (Ltemp₅₀), and low lethal time (Ltime₅₀). There were significant differences among the four populations; the northern population was more cold hardy than the southern population, and the two mid-latitude populations were intermediately cold hardy.
4. The cold hardiness of all populations was enhanced to various degrees by short-term cold acclimation at 0 °C and 5 °C. For most populations, a 2-day acclimation period seemed to be optimal.     

Age, growth, mortality and population structure of the oyster, Crassostrea madrasensis, in the Moheskhali Channel (southeastern coast of Bangladesh)

The population structure, age, growth, mortality and harvest intensity of the oyster Crassostrea madrasensis were examined in the Moheskhali Channel, Bangladesh between June 2003 and May 2004. The channel is a representative habitat for the area. C. madrasensis monthly length frequency data were analyzed using FiSAT software for estimating population parameters, including asymptotic length ( L _∝ ), growth co-efficient ( K ) and recruitment pattern to assess the status of the stock. Asymptotic length ( L∝ ) and growth co-efficient ( K ) were 20.88 cm and 0.35 year⁻¹, respectively. The growth performance index (φ') was calculated with 2.18. The growth pattern showed negative allometric growth ( b  < 3), with an asymptotic weight ( W _∝ ) of about 1124.6 g. The oyster attained an average length of 6.17 cm at the end of 1 year. Total mortality ( Z ) by length-converted catch curve was estimated at 1.78 year⁻¹, fishing mortality ( F ) at 0.77 year⁻¹, and natural mortality ( M ) at 1.01 year⁻¹. The exploitation level ( E ) of C. madrasensis was 0.43, while the maximum allowable limit of exploitation ( E _max) was 0.45 for the highest yield. The recruitment pattern was continuous, displaying a single major peak event per year. Habitat temperatures were 25.5–31.0°C (mean ± SD, 29 ± 1.62°C); salinity range was from 12.36 to 26.0 ppt (mean ± SD, 19.6 ± 4.7 ppt). The exploitation level (0.43) indicated that the oyster stock was exploited at almost maximum yield in this channel.