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  1. 1. 1 INTRODUCTION Bivalvia constitute the second largest class of Mollusca. They have a great economics importance (Abbott, 1952). Many of them are edible, while some bivalves act as intermediate hosts of several trematodes (Malek, 1962). Marine species represent about two thirds of this class, while fresh-water ones forms the remaining third. Many marine species are distributed from intertidal areas to great water depths. The majority of this group lives in sand and mud bottoms (Sharabati, 1984). In general, fouling is defined as the formation of deposits on surfaces of heat exchangers and processing equipments which impede the transfer of heat and increase the resistance of water flow. The growth of these deposits causes thermal and hydrodynamic performance of heat transfer equipment to decline with time. Fouling affects the energy of industrial processes and decides the amount of material employed in the construction of these equipments. However, it is necessary to provide extra heat transfer area to compensate the effects of fouling (Somerscales, 1979). According to Epstein (1979), fouling was classified into six distinguished categories: i. Precipitation Fouling Deposition of a solid layer on heat transfer surface mainly resulting from the existing dissolved inorganic salts in the flowing solution which become supersaturated under the process conditions. ii. Particulate Fouling Accumulation of solid particles suspended in a fluid onto a heat transfer surface leads to fouling.
  2. 2. 2 iii. Chemical Reaction Fouling In this type deposits that are formed as a result of chemical reactions in which heat exchanger surface material does not react itself but it may act as a catalyst. iv. Corrosive Fouling Fouling is due to corrosion deposits from a chemical reaction between the heat transfer surface and the heat transfer medium. v. Freezing Fouling This is developed as a result of partial solidification of the heat transfer medium on a subcooled heat transfer surface. vi. Biological Fouling This category of fouling requires deposition of a biofilm on the heat transfer surface due to bacteria, fungi and algae that is called microbial fouling. Also macrobial fouling that is attachment and growth of other macro-organisms such as barnacles, clams and mussels. Biological fouling is a common problem in chemical industry and particularly in petroleum refineries. Many species of mussels are known to be causative agents of biofouling such as Brachidontes variabilis and Modiolus barbatus (Ghobashy and El-Komy, 1981), Corbicula fluminea (Lyons et al., 1988), Dreissena polymorpha and D. bugensis (Ackerman et al., 1994), B. striatulus (Rajagopal et al., 1997), Mytilus edulis and M. galloprovincialis (Khalanski, 1998), and Perna viridis (Masilamon et al., 2002b). B. variabilis Kraus, 1848 (Feinberg, 1979) (Phylum: Mollusca; Class: Bivalvia; Subclass: Lamellibranchia; Super family: Mytilacea; Family:
  3. 3. 3 Mytilidae), the subject of the present work, is controlled through application of an appropertiate biocide (Epstein, 1979; Hare, 2000) for instance pentachlorophenol and 2-nitrophenol (Borcherding, 1992), chlorination (Ackerman et al., 1994; Rajagopal et al., 1997; Masilamon et al., 2002b), dodecyldimethylammonium chloride (Bargar and Fisher, 1997), butylated hydroxyanisole [BHA] (Cope et al., 1997), bacterial products (Armstrong et al., 2000), copper compounds (Nicholson, 2001), carbamate and gluteraldehyde (Pereira et al., 2001), or by the use of physical parameters including temperature (Masilamon et al., 2002a; Gunasingh et al., 2002). Aim of the Work The present work aims to study: i. Some ecological parameters such as pH, salinity, dissolved oxygen, temperature and some elements such as magnesium, potassium, calcium, nickel, zinc and lead at Suez Gulf. ii. Macro and microanatomy of some organs of the mussel Brachidontes variabilis. iii. Effect of some physicochemical parameters (pH, salinity), some elements (calcium, nickel, zinc and lead) and some molluscicides (gesapax, uccmaluscide, cetyl trimethylammonium chloride and copper sulfate) on survival of B. variabilis. iv. The histological changes of gills, digestive gland and ovary after exposure to the above mentioned parameters. On the other hand, successful control of the biological fouling must rely, in the first place, on the deep knowledge of the biology and the histology of pests causing it.
  4. 4. 4 HISTORICAL REVIEW Mytilidae have been the subject of investigation of many authors. Concerning Brachidontes variabilis, it could be stated that their scientific information is rather sporadic and not integrated. However, Macpherson and Gabriel (1962) and Davis (1980) described the shell of B. variabilis, while Achille and DiGeronimo (1978) made a biometric study of the same species. Feinberg (1979) studied the habitat and distribution of B. variabilis. Different marine bivalves were subjected to different values of salinities. It was found that salinity tolerance for a given species was not constant but varied with season (Castagna and Chanely, 1973). In addition, Shumway (1977) exposed eight species of bivalves to both gradual and abrupt salinity fluctuations. In seven of the tested species the water content of the muscles varied by only a small amount. Also, he concluded that the amplitude of change in tissue water content was greater in low salinity- accimilated animals than in high salinity ones. Moreover, the effects of temperature and salinity on metabolism and byssal formation of B. variabilis were studied by Stern and Achituv (1978). They also stated that mortality and survival were modified by salinity regimen. On the other hand, influence of lowering salinity on the respiratory rate of B. solisianus and Perna perna was studied by Fontes and Sonia (1981). They recorded that on diluting sea water B. solisianus appeared to be more resistant. Westerbom et al., (2002) studied the effect of lowering salinity on the growth rate of Mytilus edulis. Their results showed a marked decline in mean mussel size and biomass as salinity decreased.
  5. 5. 5 Concerning the effect of pH value on the bivalves Mercenaria mercenaria and Crassostrea virginicia, Calabrese and Davis (1966) found that the optimum pH range for growth was 7.50-8.00 and 8.25-8.50 respectively. Calabrese and Davis (1969) determined the minimum and maximum pH levels for spawning of C. virginicia, these were 6.00 and 10.00, respectively. Regarding the heavy metals in seawater of the Gulf of Suez, Abd-El Salam (1981) evaluated the range of concentrations of some heavy metals. It was found that Pb = 1.00, Cu = 1.60-9.60 and Zn = 1.62-29.22ppb. Moreover, the concentrations detected by El-Moselhy (1953) for Cd, Pb, Cu and Zn were 0.11, 1.11, 7.31 and 2.55ppb respectively in Suez Bay. Mohamed (1996) found that the concentrations of the same elements were 0.01-4.00, 0.10-21.60, 0.05-13.10 and 0.08-34.2ppb respectively in the same region. However, Yassien (1998) reported that the average concentrations of Cd, Pb, Cu and Zn were in the order 0.20, 1.95, 1.59 and 11.27ppb in Suez Bay. On the other hand, little information was known about the biological effects of heavy metals on marine bivalves. A number of studies was conducted to determine the levels of metals concentrated by bivalves. Calabrese and Nelson (1974) studied the toxicity of some heavy metals as metallic salts including nickel as nickel chloride, zinc as zinc chloride and lead as lead nitrate on the subsequent development of Mercenaria mercenaria. It was found that LC50 was 0.31ppm for Ni, 0.17ppm for Zn and 0.78ppm for lead. Brereton et al., (1973) reported that Zn caused total mortality to Crassostrea gigas and Ostrea edulis at doses 0.10 and 0.50ppm respecively.
  6. 6. 6 Concerning biocides, Cremyln (1978) reported that simazine and atrazine were initially introduced as triazine-based herbicides. Later on, deNoyelles et al., (1982); Thurman et al., (1992) and Pereira and Hostetler (1993) approved that atrazine was extensively used as herbicide. In other words, the triazine herbicides were not regarded as molluscicides. The effect of other biocides such as bayluscide (a commercial formula of niclosamide amine salt) on the mussel Dreissena polymorpha was examined by Hoestlandt (1971). He tested its toxicity as compared to other biocides such as Frescon (insecticide). It was found that bayluscide was 4 times toxic. Moreover, Fisher and Dabrowska (1994) developed methods for measuring the toxicity of Bayer 73 (a formula of niclosamide amine salt) for several stages of D. polymorpha. They evaluated the toxicity of this biocide after 24hours static tests, where they found that the sensitivity of zebra mussel varied as the life stages varied, whereas the adults were less sensitive. In addition, quaternary ammonium compounds were used to control the biofouling mussel D. polymorpha (Lyons et al. 1988 and Martin et al., 1993). Zebra mussel was also controlled by quaternary ammonium compositions (1:2 mixt. of poly (dimethyl diallylammonium chloride and didecyl dimethylammonium chloride) within 72hours (Muia and Donlan, 1990). D. polymorpha were statically exposed to various concentrations (0.5, 1.0, 2.0, 4.0 and 8.0ppm) of a polyquaternary ammonium compound was killed at all tested concentrations (McMahon et al. 1990). Fellers et al., (1990) totally controlled these mussels using 5ppm of aliphatic quaternary ammonium compound (Duomeen C) after 4days of exposure.
  7. 7. 7 On the other hand, copper sulfate was found to possess molluscicidal properties, and it was used in many parts of the world, especially in Egypt and Middle East (Malek and Cheng, 1974). However, Vyskebets et al., (1976) studied controlling biological fouling formed in industrial water- supply system applying a copper compound (copper tetramine sulfate) at 5-10ppm. Moreover, Calabrese et al. (1977) investigated the toxicity of