Control of Modiolid Mussels in Cooling Water Systems by Continuous Chlorination

Modiolid mussels such as Modiolus philippinarum and Modiolus metcalfei constitute a numerically significant group in fouling communities, especially in tropical and subtropical industrial cooling water systems. Nevertheless, there are hardly any published reports on the tolerance of these species to chlorination or biofouling control measures, This article provides data on the mortality pattern (LT₅₀ and LT₁₀₀) and physiological activities (oxygen consumption, filtration rate, foot activity, and byssus thread production) of different size groups of M. philippinarum (7- to 30-mm shell lengths) and M. metcalfei (6- to 26-mm shell lengths) exposed to different concentrations of residual chlorine (0.25, 0.50, 0.75, and 1.00 mg/L for sublethal responses; 1, 2, 3, and 5 mg/L for mortality). It is shown that exposure time for 100% mortality of M. philippinarum and M. metcalfei significantly decreased with increasing residual chlorine concentration. For example, 30-mm size group M. philippinarum exposed to 1 mg/L chlorine residual took 402 h to reach 100% mortality, whereas those exposed to 5 mg/L chlorine took 108 h. Among the two mussels, M. philippinarum showed slightly higher tolerance (9–20%) to chlorine when compared to M. metcalfei. The effect of mussel size on mortality of M. philippinarum was significant, with the larger size group mussels showing greater resistance than smaller ones. However, in M. metcalfei, size of the mussel does not seem to be a determinant of its chlorine tolerance. All size groups of M. philippinarum and M. metcalfei showed progressive reduction in physiological activities (oxygen consumption, filtration rate, foot activity index, and byssus thread production) when chlorine residuals gradually increased from 0 to 1 mg/L. Reduction in physiological activities was strongly correlated with chlorine concentration. A comparison of present data with data available for other coexisting mussel species suggests that M. philippinarum and M. metcalfei are relatively less tolerant to chlorine than Perna viridis, Perna perna, and Brachidontes striatulus, which also cause fouling problems in tropical coastal waters.     

Response of fouling brown mussel,Perna perna (L.), to chlorine

Perna perna (L.), the edible brown mussel, is very widely distributed in the tropical and subtropical regions and is commonly found in rocky shores. Apart from being a candidate for commercial cultivation, P. perna is also a common pest organism in cooling water systems of coastal power stations. Therefore, a lethal and sublethal response of this mussel to commonly used antifouling biocides is of considerable interest to the industry. Mortality pattern (LT(50) and LT(100)) and physiological activities (oxygen consumption, filtration rate, foot activity index, and byssus thread production) of different size groups (9-34 mm shell lengths) of P. perna were studied in the laboratory under different residual chlorine concentrations (0.25, 0.50, 0.75, and 1.00 mg/L for sublethal responses and 1, 2, 3, and 5 mg/L for mortality). Results showed that exposure time for 100% mortality of mussels significantly decreased with increasing residual chlorine concentration. For example, mussels of 9 mm size group exposed to 1 mg/L chlorine residual took 384 h (16 days) to reach 100% mortality, whereas those exposed to 5 mg/L chlorine took 84 h (4 days). The effect of mussel size on mortality was significant between 1 mg/L and 5 mg/L residual chlorine, with larger mussels showing greater resistance than smaller ones. For example, at 2 mg/L residual chlorine, 9 mm and 34 mm size group mussels took 228 h (10 days) and 304 h (13 days), respectively, to achieve 100% mortality. All size groups of P. perna showed progressive reduction in physiological activities, when chlorine residuals were gradually increased from 0 to 1 mg/L. Reduction in physiological activities was strongly correlated with the residual level. A comparison of present data with data available for other common fouling organisms suggests that P. perna is relatively less tolerant to chlorine than Perna viridis (L.) and Brachidontes striatulus (Hanley), which also cause fouling problems in tropical coastal waters.     

Control of Brackish Water Fouling Mussel, <Emphasis Type="Italic">Mytilopsis leucophaeata</Emphasis> (Conrad), with Sodium Hypochlorite

Though the Conrad's false mussel, Mytilopsis leucophaeata, is an important fouling animal in industrial cooling water systems, there are no published reports on the tolerance of this species to chlorination. A series of experiments was conducted to determine the effects of mussel size (2–20 mm shell length), season (breeding versus nonbreeding), nutritional status (fed versus starved) and acclimation temperature (5–30°C) on the mortality pattern of M. leucophaeata under continuous chlorination (0.25–5 mg/L). The effect of mussel size on M. leucophaeata mortality in the presence of chlorine was significant, with 10 mm size group mussels showing greater resistance. At 0.25 mg/L residual chlorine, 2 mm size group mussels took 89 days to reach 100% mortality, whereas 10 mm size group mussels took 109 days. M. leucophaeata collected during nonbreeding season (December–April) was more tolerant to chlorine than those collected during breeding season (June–October). Nutritional status of the mussel had no significant influence on the chlorine tolerance of the mussel: fed and starved mussels succumbed to chlorine at equal rates. The effect of acclimation temperature on M. leucophaeata mortality in the presence of chlorine was significant. At 0.5 mg/L residual chlorine, mussels acclimated at 5°C required 99 days to reach 95% mortality, whereas mussels acclimated at 30°C required 47 days. A comparison of present data with previous reports suggests that resistance of M. leucophaeata to chlorination is higher than other mussel species causing fouling problems in The Netherlands (Mytilus edulis and Dreissena polymorpha). Received: 18 October 2001/Accepted: 4 March 2002     

Control of brackish water fouling mussel,Mytilopsis leucophaeata (Conrad), with sodium hypochlorite

Though the Conrad's false mussel, Mytilopsis leucophaeata, is an important fouling animal in industrial cooling water systems, there are no published reports on the tolerance of this species to chlorination. A series of experiments was conducted to determine the effects of mussel size (2-20 mm shell length), season (breeding versus nonbreeding), nutritional status (fed versus starved) and acclimation temperature (5-30 degrees C) on the mortality pattern of M. leucophaeata under continuous chlorination (0.25-5 mg/L). The effect of mussel size on M. leucophaeata mortality in the presence of chlorine was significant, with 10 mm size group mussels showing greater resistance. At 0.25 mg/L residual chlorine, 2 mm size group mussels took 89 days to reach 100% mortality, whereas 10 mm size group mussels took 109 days. M. leucophaeata collected during nonbreeding season (December-April) was more tolerant to chlorine than those collected during breeding season (June-October). Nutritional status of the mussel had no significant influence on the chlorine tolerance of the mussel: fed and starved mussels succumbed to chlorine at equal rates. The effect of acclimation temperature on M. leucophaeata mortality in the presence of chlorine was significant. At 0.5 mg/L residual chlorine, mussels acclimated at 5 degrees C required 99 days to reach 95% mortality, whereas mussels acclimated at 30 degrees C required 47 days. A comparison of present data with previous reports suggests that resistance of M. leucophaeata to chlorination is higher than other mussel species causing fouling problems in The Netherlands ( Mytilus edulis and Dreissena polymorpha).     

<Emphasis Type="Italic">Cryptosporidium</Emphasis> spp. Contamination in <Emphasis Type="Italic">Perna perna</Emphasis> Mussels Destined for Human Consumption in Southeastern Rio de Janeiro,Brazil

Cryptosporidium spp. has been recognized as an important pathogen. As bivalve mollusks are noted as potential sources of several pathogens due to their consumption as foodstuffs, the aim of this study was to investigate the occurrence of Cryptosporidium spp. oocysts in Perna perna mussels and in seawater samples from a mussel farm in Southeastern Brazil, where mussels are grown directly in the sea, attached to ropes. Oocysts were observed by microscopy and confirmed by an enzyme-linked immunosorbent assay. Oocysts were present in mussel gills and GI tracts, as well as in the seawater. Of the 100 females, 10% and 11% showed contaminated GI tracts and gills, respectively, while this rate was lower in males, at 5% and 8.9%. Oocysts were present in higher amounts in the GI tract compared to gills and water. Contamination of the study area is apparent, leading to public health risks. More in-depth studies are needed, including molecular investigations, to identify Cryptosporidium species in mussels, as well as the implementation of monitoring actions in animals destined for human consumption.     

Effect of Dibutyl Phthalate on the Tolerance and Lipid Accumulation in the Green Microalgae <Emphasis Type="Italic">Chlorella vulgaris</Emphasis>

Offshore oil exploration creates threats to coastal ecosystems, including increasing urbanization and associated effluent releases. Genotoxicity biomarkers in mussels were determined across a gradient of coastal zone influences of offshore petroleum exploration in southeastern Brazil. Coastal ecosystems such as estuaries, beaches and islands were seasonally monitored for genotoxicity evaluation using the brown mussel Perna perna. The greatest DNA damage (5.2%?±?1.9% tail DNA and 1.5‰? ±?0.8‰ MN) were observed in urban estuaries, while Santana Archipelago showed levels of genotoxicity near zero and is considered a reference site. Mussels from urban and pristine beaches showed intermediate damage levels, but were also influenced by urbanization. Thus, mussel genotoxicity biomarkers greatly indicated the proposed oil exploration and urbanization scenarios that consequently are genetically affecting coastal organisms.     

Acute toxicity of copper, ammonia, and chlorine to glochidia and juveniles of freshwater mussels (Unionidae)

The objective of the present study was to determine acute toxicity of copper, ammonia, or chlorine to larval (glochidia) and juvenile mussels using the recently published American Society for Testing and Materials (ASTM) Standard guide for conducting laboratory toxicity tests with freshwater mussels. Toxicity tests were conducted with glochidia (24- to 48-h exposures) and juveniles (96-h exposures) of up to 11 mussel species in reconstituted ASTM hard water using copper, ammonia, or chlorine as a toxicant. Copper and ammonia tests also were conducted with five commonly tested species, including cladocerans (Daphnia magna and Ceriodaphnia dubia; 48-h exposures), amphipod (Hyalella azteca; 48-h exposures), rainbow trout (Oncorhynchus mykiss; 96-h exposures), and fathead minnow (Pimephales promelas; 96-h exposures). Median effective concentrations (EC50s) for commonly tested species were >58 microg Cu/L (except 15 microg Cu/L for C. dubia) and >13 mg total ammonia N/L, whereas the EC50s for mussels in most cases were <45 microg Cu/L or <12 mg N/L and were often at or below the final acute values (FAVs) used to derive the U.S. Environmental Protection Agency 1996 acute water quality criterion (WQC) for copper and 1999 acute WQC for ammonia. However, the chlorine EC50s for mussels generally were >40 microg/L and above the FAV in the WQC for chlorine. The results indicate that the early life stages of mussels generally were more sensitive to copper and ammonia than other organisms and that, including mussel toxicity data in a revision to the WQC, would lower the WQC for copper or ammonia. Furthermore, including additional mussel data in 2007 WQC for copper based on biotic ligand model would further lower the WQC.     

Monitoring Trace Metal Contaminants in Green Mussel, Perna viridis from the Coastal Waters of Karnataka, Southwest Coast of India

The green mussel (Perna viridis) is widely distributed in the coastal waters of Asia and is used in mussel watch programmes for monitoring environmental contaminants throughout the region. Green mussels representing different size groups and habitats were sampled from their natural beds at 28 locations in the inshore waters of Karnataka (southwest coast of India) to analyze the tissue concentrations of Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn. Tissue concentrations of Cr, Cu, Fe, and Pb were significantly higher in smaller mussels than in the larger size group. Significantly higher concentrations of Cr, Cu, Fe, Mn, and Ni were observed in mussels sampled from intertidal beds when compared to mussels from the subtidal beds. The sampling sites were categorized into industrial sites (IS), urban sites (US), and nonurban sites (NS) based on principal component analysis of metal concentrations in mussel. Spatial variations in tissue concentrations of all metals were observed except for Zn. Generally, the levels of toxic trace metals like Pb, Cd, Ni, and Cr in the whole tissue of P. viridis were within safe limits throughout the coast of Karnataka. However, relatively high concentrations of Cd, Cr, and Pb were observed in the whole tissue of green mussels collected from the industrial sites (IS), which may be derived from a variety of anthropogenic activities.     

Polybrominated Diphenyl Ethers (PBDES) and Polychlorinated Biphenyls (PCBS) in Mussels and Two Fish Species from the Estuary of the Guanabara Bay, Southeastern Brazil

The present investigation aimed to analyze PBDE and PCB contamination in mussels (Perna perna) and two commercially important fish species, croaker (Micropogonias furnieri) and mullet (Mugil liza), in the Guanabara Bay, the most important Brazilian estuary, by gas chromatography coupled to mass spectrometry, in order to further knowledge regarding these compounds in the southern hemisphere. This is also the first report of PBDE in this mussel species in the Guanabara Bay. Fish were captured in September (dry season, winter) and March (wet season, summer) 2007 and September 2008. Mussels were collected in August (dry season, winter) 2006, in February (wet season, summer) 2007, and in August 2007 (winter). The results show that all samples showed higher PCB contamination when compared to other ecosystems around the world. On the other hand, PBDEs presented lower concentrations in 41 % of the samples. Croakers presented the highest PCB and PBDE levels, with mullet showing intermediary values and mussels, the lowest.     

Toxicity of organophosphorus insecticides in the zebra mussel, Dreissena polymorpha P.

The 96-h toxicity of four organophosphates (thiometon, disulfoton, malathion, and demeton-S-methyl, the oxygen analogue of thiometon) in the freshwater bivalve mollusc Dreissena polymorpha was tested using different nominal concentrations ranging between 6 and 50 mg/L. No mortalities were observed in mussels exposed to malathion and demeton-S-methyl (26 mg/L and 6 mg/L, respectively), and at the lowest concentrations of thiometon and disulfoton (6 and 10 mg/L, respectively). At higher thiometon and disulfoton concentrations, mortalities occurred. At the highest concentrations of 50 mg thiometon/L and 30 mg disulfoton/L, mussel mortalities of 88 and 93%, respectively, were determined. Organophosphate concentrations of up to a factor 10 times higher than in the ambient water were found in exposed mussels, irrespective of whether they were alive or dead. The search for organophosphate metabolites via GC/MS analysis of mussel tissue extracts was negative, suggesting lacking or low oxidative activation of the insecticides used. The mollusc is highly resistant to toxic effects of organophosphate insecticides and their biological active oxygen analogues.     

Control of the Biofouling Mollusc,Dreissena polymorpha (Bivalvia: Dreissenidae), with sodium hypochlorite and with polyquaternary ammonia and benzothiazole compounds

Small adult zebra mussels (Dreissena polymorpha), 2–8 mm valve length, collected from Lake St. Clair were exposed to a range of concentrations of three biocides in static, acute toxicity tests in the laboratory. Laboratory conditions (22°C; pH 7.8; water hardness 100 mg/L) were representative of midsummer conditions in the nearshore of Lakes Erie and St. Clair. Mussels actively colonized styrene test substrates which were transferred to three replicate, 1-L test vessels. Sodium hypochlorite was an effective biocide at concentrations exceeding 1.00 mg/L and resulted in complete mortality of mussels by 157 and 264 h at concentrations of 5.00 and 2.50 mg/L, respectively. Poly [oxyethylene (dimethylimino) ethylene (dimethylimino) ethylene dichloride] at 1,2,4 and 8 mg/l and (2-(thiocyanomethylthio) benzothiazole) at 0.5,1,2 and 4 mg/L resulted in 100% mortality at all concentrations in times ranging from 144 to 250 h and 110 to 192 h, respectively. Biocide concentration significantly affected the mean time of death for all three of the compounds tested. Mussel valve length had a significant positive effect on time of death in (2-(thiocyanomethylthio) benzothiazole) but only explained a maximum 18% of the variance. Resistance of these actively colonizing mussels to biocides was greater than that found by other laboratory studies, perhaps because of lowered handling stress in our experimental manipulations.     

Trace Metal Content in Mussels, Perna viridis L., Obtained from Selected Seafood Markets in a Metropolitan City

Mussels, Perna viridis L., obtained from three selected seafood markets in Metro Manila, were tested for metal content including cadmium, copper, lead, and zinc through atomic absorption spectrophotometry. Water samples from Bacoor Bay, Cavite, which supplies mussels to the market, were likewise subjected to similar metal analyses. Of the metals analyzed in the soft tissues of mussels, only copper and lead with highest obtained values of 10.4 mg/kg and 2.3 mg/kg, respectively exceeded the PEMSEA guideline for safe human consumption. Water samples collected from the harvest sites in Bacoor Bay showed high concentrations of cadmium (0.023 mg/L) and lead (0.25 mg/L) that exceeded the standards of DENR, ASEAN, and US EPA. Zinc, though detected in relatively high concentrations in both water (0.03 mg/L) and soft tissues (12.16–14.43 mg/kg) of mussels remained below the criteria set by the above-mentioned agencies. Overall, the present study indicates that mussels being sold in selected Metro Manila seafood markets were contaminated with metals, notably Cu and Pb, at concentrations that are unsafe for human consumption and thus, represents a health risk.     

Control of the freshwater fouling bivalveCorbicula fluminea by halogenation

Mortality levels for adult and juvenile Asiatic clam,Corbicula fluminea, were determined after exposure to halogens (chlorine, bromine) in 28 to 32-day laboratory and field (industrial water supply) tests. Low levels of mortality (<53%) were generated in laboratory studies on exposure to constant doses of total residual chlorine (TRC) when mean test temperatures were <16C. Mortality levels were elevated (>53%) when test specimens were exposed to comparable TRC levels (0.2 to 1.0 mg/L) at temperatures in excess of 18C. Mortalities generated among adults by an initial 14-day low dose (0.25 mg/L TRC) followed by an 18-day high dose (0.50 to 1.00 mg/L TRC; >80% mortality) were comparable to those from a constant high dose (0.50 to 1.00 mg/L; 60 to 95% mortality). Adults and juveniles were comparably sensitive to halogen concentrations adequate for control. There is no substantial difference in the effectiveness of either chlorine or bromine in controlling adult and juvenile stages ofC. fluminea. Field studies conducted in the spring and fall produced markedly dissimilar results. Mortality levels during the spring field study exceeded 90% after 28 days of exposure to 0.25 mg/L TRC, while ambient temperatures rose from 20 to 25C. Mortality levels not exceeding 23% were observed among test organisms after 28 days of exposure to elevated TRC levels (<0.50 mg/L), while ambient temperatures were declining from 20 to 12C during October and November 1985.     

Effects of season,stock, and laboratory protocols on survival of zebra mussels (Dreissena polymorpha) in bioassays

A series of experiments were conducted to determine the effects of maintenance method (fed or starved), stock location, season, mussel size, and rate of acclimation to temperature on the responses (mortality) of zebra mussels in bioassays. Mussels maintained on a diet of crushed Chlorella are more tolerant to Bayer 73^® and more sensitive to sodium hypochlorite than starved mussels. Variability in LC50s of zebra mussels is high during the first 60 days in the laboratory, after which the resistance of mussels to both hypochlorite and Bayer 73^® declines with reductions in body condition. Zebra mussels collected during the early summer and late fall are more tolerant to both hypochlorite and Bayer 73^®. There is significant variation in tolerances to biocides depending on the stock, such that stocks from locations with more degraded water quality have increased tolerances. Acclimating mussels from 4 to 20°C at rates of 2 and 10°C d^–1 does not significantly affect tolerance to biocides. In general, LC50s of mussels vary by only 2–3×, suggesting that mussels from any location, any season, and maintained under any maintenance protocol can be used in range-finding tests. Comparisons of results among studies requires knowledge of mussel stock, collection season, and laboratory maintenance protocols.     

Acute Toxicity of Potassium to the Adult Zebra Mussel Dreissena polymorpha

The acute toxicity of potassium (K⁺) to adult zebra mussels, Dreissena polymorpha, and the efficacy of using K⁺ to enhance the toxicity of a commercial biocide was examined. Mussels, 15–20 mm in total shell length, collected from Lake Ontario, were exposed to static concentrations of K⁺ for 3, 6, 12, and 24 h, and to a sublethal concentration of K⁺ prior to and during exposure to Clam-Trol^? CT-2 for 6, 12, and 24 h. Tests were conducted at ambient lake temperatures of 12°C and 22°C and mussels were subjected to a 96 h recovery period. Valve closure was inhibited in mussels exposed to sublethal as well as lethal concentrations of K⁺, resulting in mussels that were nonresponsive to tactile stimulation. The median effective concentration (ED₅₀) of K⁺ to induce nonresponsive mussels increased as the length of the recovery period was extended from 24 to 96 h, indicating that some nonresponsive mussels were capable of recovering 96 h after exposure to the K⁺ treatments. A recovery period duration of 96 h was critical in assessing mortality in mussels exposed to high K⁺ levels and the use of tactile stimulation to test for valve responsiveness was insufficient to identify mortality. The 24 h median lethal concentration (LC₅₀) of K⁺ at 22°C (400 mg/L) was found to be sixfold higher than the LC₅₀ reported by other investigators utilizing shorter recovery periods. The LC₅₀ of the biocide to mussels treated with K⁺ was not reduced, suggesting that the use of K⁺ to inhibit valve closure may not be useful in methods to control mussel infestations. Received: 25 March 1997/Accepted: 15 October 1997     

Biochemical Composition, Growth, and Survival of the Guppy, Poecilia reticulata, During Chronic Sublethal Exposure to Cadmium

The survival, growth, and biochemical composition (protein, total lipid, total carbohydrate, free reducing sugars, RNA, DNA) of the guppy, Poecilia reticulata, exposed to low sublethal concentrations of cadmium throughout its life cycle (beginning with 5-day-old juveniles) was studied. The purpose was to get some insight on the cause of metal toxic effects and evaluate the utility of monitoring levels of biomolecules as bioindicators of chronic toxicant effects on fish. The LC₅₀ (48 h) of cadmium for 5-day-old Poecilia was 56.77 mg/L. The median lethal times (LT₅₀) of Poecilia exposed to low cadmium concentrations (0.5–5 mg/L) ranged from 7.65 to 72.51 days, and could be accurately predicted by the mortality observed after 20 days of exposure. The whole-body dry weight increase of cadmium-exposed guppies presented a decline from that of the controls. These declines were statistically significant after 20 days of exposure to concentrations higher than 1 mg/L and after 30 days to concentrations higher than 0.5 mg/L. The percentage content in RNA was the only variable from the studied macrobiomolecules that significantly decreased when guppies were exposed to Cd concentrations higher than 0.5 mg/L for 30 days. The same trend was apparent in the ratio RNA/DNA. However, the ratio protein/RNA/DNA significantly increased after 10 days of growth to 1.5 mg/L and after 20 days to concentrations higher than 0.5 mg/L, thus having a predictive value for early-life history stages of Poecilia exposed to Cd. Received: 15 May 1997/Accepted: 6 January 1998     

Chronic toxicity of copper and ammonia to juvenile freshwater mussels (Unionidae)

The objectives of the present study were to develop methods for conducting chronic toxicity tests with juvenile mussels under flow-through conditions and to determine the chronic toxicity of copper and ammonia to juvenile mussels using these methods. In two feeding tests, two-month-old fatmucket (Lampsilis siliquoidea) and rainbow mussel (Villosa iris) were fed various live algae or nonviable algal mixture for 28 d. The algal mixture was the best food resulting in high survival (>or=90%) and growth. Multiple copper and ammonia toxicity tests were conducted for 28 d starting with two-month-old mussels. Six toxicity tests using the algal mixture were successfully completed with a control survival of 88 to 100%. Among copper tests with rainbow mussel, fatmucket, and oyster mussel (Epioblasma capsaeformis), chronic value ([ChV], geometric mean of the no-observed-effect concentration and the lowest-observed-effect concentration) ranged from 8.5 to 9.8 microg Cu/L for survival and from 4.6 to 8.5 microg Cu/L for growth. Among ammonia tests with rainbow mussel, fatmucket, and wavy-rayed lampmussel (L. fasciola), the ChV ranged from 0.37 to 1.2 mg total ammonia N/L for survival and from 0.37 to 0.67 mg N/L for growth. These ChVs were below the U.S. Environmental Protection Agency 1996 chronic water quality criterion (WQC) for copper (15 microg/L; hardness 170 mg/L) and 1999 WQC for total ammonia (1.26 mg N/L; pH 8.2 and 20 degrees C). Results indicate that toxicity tests with two-month-old mussels can be conducted for 28 d with >80% control survival; growth was frequently a more sensitive endpoint compared to survival; and the 1996 chronic WQC for copper and the 1999 chronic WQC for total ammonia might not be adequately protective of the mussel species tested. However, a recently revised 2007 chronic WQC for copper based on the biotic ligand model may be more protective in the water tested.     

Influence of rearing water temperature on induced gonadal development and spawning behaviour of tropical green mussel,Perna viridis

ObjectiveTo standardize the technique of induced breeding and spawning of green mussel Perna viridis (P. viridis), in captivity.MethodsIn Experiment-A, the temperature was increased at a rate of 2 °C/5 days interval. In Experiment-B, a rise of 3 °C/5 days was practiced, whereas in Experiment C and D, respectively 4 and 5 °C was increased in 5 days interval. The temperature was maintained constant at 20 °C in the Control.ResultsThe increase in temperature showed a progressive effect on the gonadal development of mussels. The gonads ripped at 30 to 32 °C in all the experimental tanks, irrespective of the difference in temperature hike. Complete spawning in P. viridis was achieved by gradually raising the temperature from 20 to 35 °C at a rate of 3 or 4 °C/5 days.ConclusionAccording to the present study temperature induced spawning method is very simple and cost effective and can accelerate the production of mussel seeds in hatchery units and further stock improvement through genetic manipulation.     

Effects on ionic composition of blood and tissues ofAnodonta grandis grandis (Bivalvia) of an addition of aluminum and acid to a lake

To test the hypothesis that summer low pH, episodic events cause stress and mortality in aquatic organisms including mussels, alum (aluminum sulfate) was added near the point of inflow to Lake 114 in the Experimental Lakes Area, northwestern Ontario from 3 to 5 July 1984. Lake 114 was at pH 5.9 before the alum addition. The alum produced measured extremes of pH 4.5 and [Al] of 2,237 g/L near the point of addition. This study examined the effects of the alum addition on ionic concentrations of blood and tissue (gills, adductor muscle, foot and visceral mass) of the floater mussel,Anodonta grandis grandis. Mussels were collected from a second lake, 377, and introduced into Lake 114 at five locations five days before the alum addition. In response to transfer from the oligotrophic, unmanipulated Lake 377 to acidified Lake 114 (pH 5.9), blood of mussels showed a marked elevation of [Ca⁺⁺], decline in [Mg⁺⁺] and a temporary increase in [Cl^–] but no change in [Na⁺], [K⁺] or [SO₄ ⁼]. During the alum addition, in mussels near the point source of the alum addition, blood [Na⁺] and [Cl^–] declined and [Ca⁺⁺] became still more elevated. Mussels suffered no mortality associated with the alum addition and almost no mortality during 26 days in Lake 114. Gill increased in [Al], [Ca], [Mn], declined in [Na] and showed no change in [Cd] in mussels near the alum addition. Visceral mass and adductor muscle also had lower [Na] in mussels near the point of alum addition. We attribute the increase in blood [Ca⁺⁺] to the dissolution of the Ca stores in the shell and/or mantle of mussels. This would provide protection to the mussels during short-term declines in pH such as spring or summer episodic events. Never-theless, chronic exposure to small decreases in pH by mussels, already near the limits for obtaining sufficient Ca⁺⁺, might be intolerable. It follows that acidification to the pH of 5.9 of soft water lakes containing mussels would be expected to lead to the loss of A.g. grandis from these waters.     

A comparison between particulate (elemental) zinc and soluble zinc (ZnCl2) uptake and effects in the mussel,Mytilus edulis

The uptake of particulate (elemental) and soluble (ZnCl₂) zinc was compared in whole animals and individual organs in the mussel Mytilus edulis. Analysis of seawater showed that the addition of particulate zinc resulted in a maximum concentration of 0.7 g/g dissolved zinc being present in the aquaria. Mussels exposed to either form of zinc at 10 µg/g accumulated it readily, although considerable mortality was experienced after 14 days. After loading with particulate zinc, depuration for 48 h significantly lowered (p<0.001) the concentration of zinc in whole mussels. Mussels loaded at 2 µg/g showed a similar pattern of accumulation to those exposed at 10 µg/g, although with a lower mortality. Greater whole body concentrations were obtained with particulate zinc than with soluble zinc. On an organ basis, the kidney, gill, hepatopancreas, and mantle were the major sites of accumulation following both soluble and particulate zinc loading, although generally the levels were lower with particulate loading, indicating the possible presence of two different uptake pathways. The flesh condition index of mussels subjected to 10 µg/g particulate zinc declined compared to the control animals. Degeneration of the digestive tubules and the stomach was visible in zinc-loaded mussels while no such tissue damage was seen in control animals. Tissue damage, as indicated by the presence of large quantities of lipofuschin, occurred in the hepatopancreas and gonads of particulate zinc-loaded mussels. The results indicate that soluble zinc is both absorbed and taken up by the tissues far more readily than is particulate zinc, and these results may be of significance with regard to zinc loading in the mussel Mytilus edulis.