Laboratory culture of juvenile stages of the California spiny lobster Panulirus interruptus (Randall) at elevated temperatures

Puerulus stage individuals of Panulirus interruptus from coastal waters off San Diego, California, were cultured through juvenile stages at constant temperatures of 22 and 28 °C in closed-system aquaria. In these laboratory trials juveniles exhibited average growth rates of approx. 3.3 mm increase in carapace length (CL) per month at 22 °C, and approximately 4.5 mm per month at 28 °C. These rates, respectively, are about two and three times greater than estimated growth rates of juveniles in nature at ambient southern California ocean temperatures. Accelerated growth at elevated temperatures was associated with increased moulting rates (reduced intermoult periods) rather than with greater increments per moult. Aquaculture of P. interruptus juveniles at elevated temperatures appears feasible, but currently is dependent on locating areas where puerulus or post-puerulus stages can be obtained in quantity without adversely affecting natural populations.     

Post-transport recovery of cultured scallop (<Emphasis Type="Italic">Pecten maximus</Emphasis>) spat,juveniles and adults

High mortality associated with transport operations in scallop culture has been a major problem faced by European farmers. Simulated transport with Pecten maximus L. spat <2 mm, spat 15–30 mm, juveniles 30–50 mm and adults >100 mm were carried out in Spain, Ireland and Norway. Different time and temperature combinations were studied in order to maximise post-transport survival and establish best practices. Out-of-water transport could result in 100% survival if conditions were right, but the response to emersion stress depended on size, season and location. Post-transport recovery decreased with emersion time and was strongly influenced by temperature. Air exposure was tolerated for a longer time by adult scallops than spat and juveniles, but the results differed among trials in the different countries. The maximum emersion time that gave post-transport survival ≥80% was 12 h for the smallest spat, 18 h for larger spat and 24 h for juvenile and adult scallops. Adults were less affected by transport temperatures that deviated from ambient seawater temperature than spat and juveniles. In general post-transport recovery was high when sea temperature was <10°C, but during warm-water seasons special care should be taken to avoid stressful and lethal transport conditions. A transport temperature <12°C was recommended, though not more than 10°C below ambient culture temperature. A maximum transport time of 9 h was suggested for spat and juveniles to attain post-transport survival close to 100%, but 12–24 h was feasible during the cold-water season or at favourable transport temperatures.     

Recruitment and movement of the hard clam Meretrix lusoria in a tidal river of northern Kyushu,Japan

Size-frequency distributions of Meretrix lusoria, a commercially important bivalve in Japan, were compared among 6 sites in tidal flats of a small river in Kafuri Bay, northern Kyushu, Japan during 2006–2008. In Kafuri Bay, the hard clam resource is strictly managed and mean biomass of this species on the fishing ground (about 1.5 km²) exceeded 1.5 kg m^?2 in 2008. Small clams (<5 mm in shell length, SL) were most abundant in the border area between the river and the sea, while large clams (>40 mm SL) were rare there. In contrast, in the lower site of the marine area (site L), most clams were >30 mm SL. These results indicate that small clams move from riverine to marine areas with growth (post-settlement movement). Year-round, very small clams (<1 mm SL) were present and clams that were 2–5 mm SL were very rare, although the spawning season is thought to occur in summer. Probably, the early growth of many new recruits is very slow and most may even be <1 mm SL in the next spring, although some clams grow to >5 mm SL in a short period of time.     

Critical swimming speed and maximum sustainable swimming speed of juvenile Pacific bluefin tuna, Thunnus orientalis

Tank wall collision is one of the major causes of mortality during the early-stage rearing of Pacific bluefin tuna, Thunnus orientalis (PBT). Therefore, to design a rearing environment that meets the needs of juvenile PBT, it is important to gather information about their swimming capabilities. We conducted experiments to examine the relative critical swimming speed (RCSS) and maximum sustainable swimming speed (MSSS) of early-stage PBT. The fish were kept in 3-tonne tanks and fed on artificial pellets every 2 h from dusk to dawn. We conducted two sets of experiments to measure swimming speed; the fish were introduced one at a time into a water funnel, and the water current velocity was gradually increased over time to estimate RCSS, or the water current was kept at a constant velocity to estimate MSSS. We measured the RCSS of 72 PBT juveniles (24–29 days after hatching (DAH); standard length (SL), 15.0 ± 2.3 mm) and the MSSS of 32 PBT juveniles (28–37 DAH; SL, 20.0 ± 5.1 mm) in the laboratory. The RCSS ranged from 4.7 to 20.3 SL/s (average, 12.4 ± 3.3 SL/s), and the MSSS was estimated to be approximately 4 SL/s. We speculate that introducing a water current in the rearing tank of no more than 4 SL/s could positively affect the survival of juvenile PBT.     

Dietary value of gametophytes and juvenile sporophytes of the brown macroalga <Emphasis Type="Italic">Eisenia bicyclis</Emphasis> for juvenile abalone <Emphasis Type="Italic">Haliotis diversicolor</Emphasis>

The dietary value of juvenile stages (gametophyte and juvenile sporophyte) of the brown macroalga Eisenia bicyclis for post-larval and juvenile abalone Haliotis diversicolor of 2.0–6.5 mm in shell length (SL) was examined and compared with that of a benthic diatom, Nitzschia sp., in laboratory experiments. Most abalone actively fed on these diets, but there were large variations in the growth rate among the diets and among the growth stages of abalone. Growth rates of abalone fed on Nitzschia sp. were highly variable within each growth stage, but showed no clear differences among growth stages. In contrast, in abalone fed gametophytes or juvenile sporophytes, growth rates linearly increased as abalone grew. Growth rates of >60 μm SL/day were observed in juveniles of >3 mm SL fed gametophytes, and juveniles of >5 mm SL fed juvenile sporophytes. These results indicate that the dietary value of the juvenile stages of E. bicyclis for the abalone changes as they grow, and with growth juvenile abalone begin to efficiently utilize gametophytes and juvenile sporophytes in that order.     

Effect of temperature and relative humidity on the tolerance of the Japanese clam, Ruditapes philippinarum (Adams & Reeve), to air exposure

Laboratory studies showed that higher relative humidity (RH) and lower air temperature increase the tolerance of the Japanese clam, Ruditapes philippinarum (Adams & Reeve), to exposure. Aerial respiration of the clam was also measured. At high RH, the exposure time which gave 50% survival (LT₅₀) was 1.97 and 1.75 times longer than in low RH at air temperatures of 15 and 25 °C, respectively. At 15 °C, all clams previously acclimatized at 15 °C survived for 58 h at low RH and 102 h at high RH. These differences can potentially be exploited to improve the shipment of clams. The aerial respiration experiment showed that the increase of the oxygen consumption rate at 25 °C was greater than that at 15 °C, following an increase in exposure time. The aerial respiration rates of the clams were ≈ 41.6% and 50.0% of those in water at 25 and 15 °C, respectively. The survival of the clams in air was dependent on aerobic rather than anaerobic respiration.     

The effect of temperature on the energy budget of the Manila clam, <Emphasis Type="Italic">Ruditapes philippinarum</Emphasis>

In this study, the energy budget of the Manila clam, Ruditapes philippinarum, was evaluated after one-week acclimation periods at 5, 10, 15, 20, and 25°C. Small clams (151 ± 12 mg DW) and large clams (353 ± 16 mg DW) were fed with the microalgae, Isochrysis galbana. Filtration rate, ingestion rate, assimilation efficiency, oxygen-consumption rate, and ammonia excretion rate were measured. Both filtration rate and ingestion rate of small and large clams were found to be related to temperature. The highest Q ₁₀ values were measured in the range 15–20°C for both small and large clams. Assimilation efficiency of both small and large clams was not significantly influenced by temperature, although the maximum mean values were detected at 20°C. Oxygen consumption rate and ammonia excretion rate of small and large clams were found to be related directly to temperature over the entire range, with a maximum being detected at 25°C. The highest Q ₁₀ value was estimated in the range 10–15°C with regard to oxygen consumption rate, and in the range of 15–20°C with regard to ammonia excretion rate. Scope for growth (SFG) was positive at all temperatures, achieving a maximum value at 20°C in both small and large clams, primarily as a consequence of the enhanced ingestion rate which offset the concomitant elevation in the metabolic rate. In this study we have estimated the thermal optimum for this species at 20°C.     

Experimental challenges of juvenile and adult Manila clams with the protozoan Perkinsus olseni at different temperatures

Infection with Perkinsus species, primarily P. olseni, is thought to be a major cause of the decline of Manila clam populations in Japan since the 1980s. However, the pathogenicity of the infection has not been sufficiently evaluated to estimate the impact of infection on wild Manila clam populations. We experimentally challenged juvenile (3- to 6-mm shell length) and adult (18- to 22-mm shell length) Manila clams with P. olseni at 18, 23, 28, and 30 °C. Mortality was significantly higher in challenged groups than in control groups. The difference in mean mortality between the challenged and control groups (all life stages and temperatures) was only significant above a threshold of infection intensity ~10⁶ cells/g soft wet tissue (SWT). As temperature increased, the onset of mortality occurred more rapidly. The increase in mortality occurred earlier in juveniles than adults at 28 °C and lower. Our results suggest that the pathogenicity of P. olseni is higher in juveniles than in adults and at higher water temperatures. Given the infection intensities (ca. 10⁶ cells/g SWT) previously reported in wild Manila clams, the parasite likely has considerable impact on wild Manila clam populations, particularly juveniles during periods of high temperature.     

Influence of lipid level and supplemental lecithin in diet on growth,feed utilization and body composition of juvenile flounder (Paralichthys olivaceus) in suboptimal water temperatures

This study was conducted to investigate the influence of dietary lipid level and supplemental soy lecithin on growth, feed utilization and body composition of juvenile flounder reared at two suboptimal water temperatures, 12 and 17 °C. Three isonitrogenous (CP 50%) diets containing 1% squid liver oil (S7), 7% squid liver oil (S14), and a mixture of 2% soy lecithin and 5% squid liver oil (SL14) were formulated to obtain 7% and 14% of crude lipid. Triplicate groups of fish (6.3 ± 0.2 g) were fed to apparent satiation twice a day for 60 days. Weight gain, daily feed intake, feed efficiency and protein efficiency ratio were significantly higher for fish reared at 17 °C than at 12 °C. Daily feed intake was significantly decreased with the increase of dietary lipid level at the same water temperature, but weight gain was not affected by dietary lipid composition. At 12 °C, feed efficiency and protein efficiency ratio were significantly higher for fish fed the S14 and SL14 diets than those of fish fed the S7 diet, while at 17 °C feed efficiency and protein efficiency ratio of fish fed the S14 diet, which were not significantly different from those of fish fed the SL14 diet, were significantly higher than those of fish fed the S7 diet. There were no significant effects of dietary lipid composition or temperature range on the whole body contents of moisture, crude protein, lipid or ash. Dietary lipid composition and temperature affected the fatty acid content of the polar lipid from the liver; and the n-3HUFA contents such as 20:5n-3 and 20:6n-3 were higher at 12 °C than at 17 °C. The results of this study indicate that an increase of dietary lipid level from 7% to 14% has beneficial effects on feed utilization of flounder when reared in suboptimal water temperatures. The increase of water temperature from 12 to 17 °C improved growth and feed utilization, but 2% soy lecithin had no substantial effect on growth and feed efficiency of juvenile flounder.     

Critical Thermal Maximum of Juvenile Spotted Seatrout (Cynoscion nebulosus) Reared for Summer Stocking in Texas

The critical thermal maximum of juvenile spotted seatrout (SL range 18–33 mm) was determined using a temperature increase of +0.26°C per hour. The critical thermal maximum (water temperature that was lethal to 50% of the test fish [LT₅₀]) for trial 1 was LT₅₀ = 38.8°C, LT₅₀ = 39.4°C for trial 2, and LT₅₀ = 38.9°C for trial 3. Critical thermal maximums differed significantly (P < 0.05) between trials 2 and 3, whereas trial 1 did not differ among trials. This difference correlated with body size, where fish in trial 2 were significantly larger (P < 0.05) (mean = 27.6 ± 2.0 mm in SL) (mean ± SE) than the fish of trials 1 (mean = 23.1 ± 0.5 mm in SL) and 3 (mean = 21.5 ± 0.7 mm in SL), suggesting positive size dependence in the critical thermal maximum.     

PRELIMINARY EVALUATION OF SURVIVAL AND GROWTH OF JUVENILE RED DRUM (Sciaenops ocellata) IN FRESH AND SALT WATER

Heretofore few quantitative studies on the tolerance of red drum (Sciaenops ocellata Linnaeus) to freshwater (FW) or dilute sea water have been conducted. In the laboratory we subjected larval and juvenile stages of red drum to dechlorinated FW for 96 hours and found 5% survival in larvae (23-day-old, 6.2 mm SL), 70% for postlarvae (34 and 47-day-old, 16.2 mm to 19.7 mm SL) and 95% for juveniles (57-day-old, 56.9 mm SL). Survival in control salinities of 10 ppt was 90% or greater. The results indicate that tolerance to dilute media is size dependent. In a separate experiment growth of juvenile red drum (52 mm SL) over a 30-day period was compared in two raceways with flow-through supplies of dechlorinated FW, and SW of ambient (35±2 ppt) salinity. SW fish grew significantly larger (P < .01) than those acclimated to FW. Within both treatments a large size differential developed with time. Food conversion efficiency was improved and appetite drive was enhanced in the SW treatment. Percent survival after 30 days was comparably high (93%) in both treatments. Fast growth and high survival of juvenile (>20 mm SL) red drum promote the feasibility of this valuable sport and commercial species in both FW and SW aquaculture. Its potential as a control fish in FW fishery management deserves further investigation.     

Resistance of Cobia,Rachycentron canadum,Juveniles to Low Salinity,Low Temperature,and High Environmental Nitrite Concentrations

Abstract

Resistance of juvenile cobia, Rachycentron canadum, to low salinity, low temperature and high nitrite concentrations was examined under laboratory conditions. After acclimating juveniles to a salinity of 20 g/L (27.3°C), salinity was decreased by 2 g/L/day. The first fish died at a salinity of 8 g/L and 80% offish were dead within 24 hours of exposure to 2 g/L. Acclimation offish to 22.6°C (21 g/L salinity) followed by a temperature reduction of 0.53°C/day resulted in initial mortality at 12.9°C. The median-lethal temperature was 12.1°C and all fish were dead by the time the temperature reached 10.4°C. Fish exposed for 96 hours to nominal ? 32 mg/L nitrite-N survived. Results of this study indicate that cobia juveniles require a salinity and temperature of > 8.0 g/L and > 12.9°C, respectively, and that environmental nitrite should not be deleterious at concentrations normally found in aquaculture systems.     

Effect of rearing temperatures on the growth and maturation of Arctic charr (Salvelinus alpinus) during juvenile and on‐growing periods

The effect of rearing temperature on the growth and maturation of Arctic charr (Salvelinus alpinus) was investigated. Arctic charr juveniles were reared for 6 months (phase I, October–April, size range 20–500 g) at constant temperatures of 9, 12 and 15 °C and according to two temperature‐step groups (T_step) i.e. fish transferred from 15 to 12 °C or from 12 to 9 °C. All the previous treatments were then reared either at 7 °C or at 12 °C for an additional 4 months (phase II, size range 300–1000 g) and then slaughtered in August 2008. The overall growth rate was the highest at a constant temperature of 15 °C for the first 6 months of the trial, with the fish in this group being 44% and 78% heavier than the fish reared at a constant temperature of 12 or 9 °C respectively. Arctic charr showed a negative response in terms of the growth rate when transferred from higher to lower temperatures, especially for groups previously reared at 15 °C. There was a trend for higher gonadosomatic index values at the end of the experiment for groups of fish that were exposed to higher rearing temperatures during the juvenile phase i.e. 4.18% (±0.79) and 7.29% (±0.89), for the temperature groups of 12 and 15 °C, respectively, compared with 2.49% (±0.74) for the 9 °C group. Our results suggest that for the production of fish >1000 g, moderate or low temperatures (here 9 °C) should be applied during the juvenile phase in order to reduce the negative effects arising from maturation. Farmers with access to heat sources should accordingly choose more moderate rearing temperatures during the juvenile stage, especially if the fish is to be moved down in the temperature regime during the on‐growing period.     

Effects of water temperature on feeding and growth of juvenile marbled flounder <Emphasis Type="Italic">Pseudopleuronectes yokohamae</Emphasis> under laboratory conditions: evaluation by group- and individual-based methods

To determine the optimal temperature for juvenile (0 year old) marbled flounder Pseudopleuronectes yokohamae, juveniles of 40–54 mm standard length were reared at six temperature conditions in the range of 8–26 °C, using group- and individual-based methods. Growth of juveniles increased from 8 to 20 °C but decreased from 20 to 26 °C, irrespective of the rearing method used. Food intake was greatest at 20 and 24 °C compared with other temperatures, while feed conversion efficiency was greater at 20 °C than 24 °C in individual rearing. Individual rearing provided more information such as individual variations in growth and food consumption, suggesting the importance of individual-based experiments for exploring the optimal temperature for fish.     

Preservation-induced changes in morphometrics of fishes: influence on prey size-choice in juvenile walleye, Stizostedion vitreum (Mitchill)

Abstract– Juveniles of the Gulf coast population of walleye, Stizostedion vitreum , 22.4–89.9 mm SL ( n =111) shrank significantly in SL and throat diameter over 12 months after being fixed in 10% formalin for 1 week and preserved in 50% isopropyl alcohol thereafter. Significant changes in body depth and total length (TL) were also determined for select larval fish prey that juvenile walleye might encounter in nature. The relationship between fresh SL and throat diameter in juveniles of the Gulf coast population of walleye (22.4–172.4 mm SL) is: throat diameter (mm) =−0.8783 + 0.0786 SL (mm) ( r ²= 0.988, P < 0.0001, n = 135). In laboratory experiments on prey size choice, walleye selected available prey near or less than their mean throat diameter, although several larger prey (7.4% of total) were also consumed. To determine the actual spectrum of prey sizes available to juvenile piscivores, we must adjust the realized size of the predator and prey for changes caused by preservation. Preservation-induced alterations in morphology translated into errors in the perceived pattern of prey size choice in walleye. The preservation-induced changes documented in this study, which are also supported by a number of other empirical data sets, must be included when modeling the relationships between feeding ecology, morphology, growth, and ecologically relevant indices (condition factors, relative weights, etc.).     

Effect of temperature on survival,growth and malformation of cultured larvae and juveniles of the seven-band grouper Epinephelus septemfasciatus

The effects of rearing temperature (23–29 °C) during the larval and juvenile stage on survival, growth and skeletal malformations in the seven-band grouper Epinephelus septemfasciatus were investigated. The survival rate of juveniles 30–40 mm in total length emerging from eggs was higher at 25 and 26 °C (0.1–1.3 %) than at 23 °C or 27–29 °C (0.004–1.5 %). Growth (increase in total length) was accelerated at higher temperatures. The frequency of malformed individuals was lower at 25–27 °C (36.0–61.5 %) than at 23, 28 or 29 °C (65.3–76.9 %). Specific incidences of spinal curvature and centrum fusion or defects in juveniles were not related to rearing temperature. However, incidences of twisted or compressed vertebrae (6.5–64.0 %) were higher at higher temperatures, while the incidence of bifurcated neural spine was significantly higher at 23 °C (43.6–54.4 %) than at other temperatures (3.3–22.7 %). The incidence rate of spinal curvature (23.3 %) was significantly higher in juveniles with a deflated swim bladder, regardless of rearing temperature. The results of this study suggest that the optimum culture temperature for seven-band grouper is 25–26 °C, collectively considering the survival, growth and incidences of abnormalities. Our results also demonstrate the significance of identifying the conditions for swim bladder inflation to prevent spinal curvature in seven-band grouper.     

Year‐round natural spawning,early development,and the effects of temperature,salinity and prey density on captive ornate goby Istigobius ornatus (Rüppell, 1830) larval survival

Natural spawning, early development and larviculture of the ornate goby Istigobius ornatus in captivity were studied for the first time. I. ornatus spawned 46 times from 31 October 2013 to 31 October 2014. Fecundity ranged from 246 to 10,214 eggs per clutch, with an average hatching rate of 77.8% ± 9.9% (M ± SEM). Fertilized eggs (1.31–1.54 × 0.46–0.50 mm in diameter) were adhesive demersal and oval‐shaped. Embryonic development lasted 84 hr at 27.5 ± 0.5°C. Newly hatched larvae [2.12 ± 0.04 mm in total length (TL)] transformed to the juvenile stage completely when TL was 7.79 mm. Effects of different water temperatures (24, 28 and 32°C) and salinities (10, 15, 20, 25, 30, 35 and 40 g/L) on per cent survivals (%) and survival activity indices (SAIs) were tested. Survival was not significantly different under different temperatures; SAIs was significantly higher at 28°C. Larvae showed the significantly higher survival and SAIs at salinities 10–30 g/L than at 35 and 40 g/L. Effect of different prey densities on survival was significantly higher in 7 days post hatch larvae fed 20 and 30 rotifers/ml. These findings could guide future programs in captive breeding technology development and commercial production of other marine ornamental gobies.     

The effect of shade on water quality parameters and survival and growth of juvenile fluted giant clams, Tridacna squamosa, cultured in a land-based growth trial

Juvenile fluted giant clams, Tridacna squamosa (mean shell length (SL) 15.7 ± 1.9 mm, mean total wet weight (TWW) 0.3 ± 0.1 g), were cultured for 4 months in land-based nursery tanks under four shade regimes (0, 10, 55 and 80 % shade). After 4 months, there were no significant differences in survival which ranged from 98.8 ± 0.1 % in juveniles cultured under 55 % shade to 100.0 ± 0.0 % in the other treatments. The SL of unshaded juveniles was only significantly greater than that of juveniles shaded 55 and 80 %. However, the TWW of juveniles cultured with no shade was significantly greater than that of the juveniles from all other treatments. The mean growth rate of juveniles varied from 5.0 mm month^?1 for juveniles shaded 80 % to 6.9 mm month^?1 for juveniles not shaded. There was no significant difference in mean growth rate of unshaded juveniles and juveniles shaded 10 %, but only the growth rate of juveniles cultured unshaded was significantly greater than that of juveniles shaded 55 and 80 %. The organic tissue content of juveniles cultured either unshaded or shaded 55 % was significantly higher than that of juveniles shaded 80 %. In contrast, the condition index (CI) of juveniles shaded 80 % was significantly higher than the CI of juveniles cultured either unshaded or shaded 55 %. However, there was no significant difference between the CI of juveniles shaded 80 and 10 %. Growth rate of juveniles was significantly correlated with temperature, dissolved oxygen content and flow rate of seawater. While low degrees of shade increase the growth rate of juvenile T. squamosa, they also negatively affect tissue condition. A shade level of 10 % appears to be optimal as it maximises growth and maintains a high CI.     

Thermal tolerance and compatibility zones as a tool to establish the optimum culture condition of the halibut Paralichthys californicus (Ayres, 1859)

California halibut, Paralichthys californicus (Ayres, 1859) juveniles were studied to ascertain the thermal tolerance and the compatibility zone where these species can be cultivated. Juvenile halibut acclimated at 15, 18, 21 and 24 °C preferred temperatures of 15.1, 18.2, 18.5 and 24.7 °C respectively. The final preferendum (FP) was 18.4 °C, equivalent to the temperature where the physiological processes are more efficient and the optimum growth temperature of 18.02 °C was calculated using the Jobling (1981) equation. The maximum average weekly temperature that must not be exceeded in a juvenile cultivation system is 22.6 °C. Juveniles avoided temperatures of 10.8 and 29.1 °C if they were acclimated between 15 and 24 °C. The thermal tolerance range of the juvenile halibut, having low and high lethal temperatures of 5.0 and 31 °C, characterizes it as a eurythermic organism. The tolerance of the halibut did not increase with the acclimation temperature corresponding to the ultimate upper incipient lethal temperature of 31 °C that differed by only 0.83 °C to the value calculated using the Jobling (1981) equation. The thermal tolerance and compatibility zone for the California halibut were 242.8 and 121.5 (°C)², respectively; they characterize the thermal niche that includes the FP supporting an optimal growth of juveniles.     

Village-based farming of the giant clam, Tridacna gigas (L.), for the aquarium market: initial trials in Solomon Islands

Between 1989 and 1992, small-scale grow-out trials of cultured Tridacna gigas (L.) were established at 40 coastal villages in Solomon Islands. The juvenile giant clams were delivered to village participants at a mean size of 34.6 mm shell length (SL) and a mean age of 380 days. The clams were grown in cages of wire mesh placed on trestles in shallow, subtidal, coral reef habitats. After a mean grow-out period of 297 days, the clams were a mean size of 77.6 mm SL, a suitable size for sale to the aquarium market. Mean growth rate was 4.1 mm month^?1. In 32 of the 53 cages involved in the trials, all clams were removed completely from the cage every 3 months for cleaning. The mean survival rate of these clams was 54%. The clams in the remaining 21 cages were not removed for cleaning and their survival was significantly lower (22%). The growth rate of clams removed for cleaning (3.7 mm month^?1) was, however, significantly lower than the growth rate of undisturbed clams (4.8 mm month^?1). At current prices for juvenile T. gigas in the aquarium trade, farmers who regularly cleaned clams would have netted a minimum of US$180 for a cage initially stocked with 390 clams. Fanners who did not clean their clams would have netted only US$40 per cage due to poorer survival.