Mussel cultivation: a practical manual (2023)

2.1 Taxonomy and Anatomy

2.1.1 Introduction

Some knowledge of mussel biology is needed to understand how a mussel hatchery works and to help solve any problems that arise. The intention here is not to provide a detailed description of the biology of the mussels, but rather to provide a brief summary of information relevant to the operation of the hatchery. There are several excellent texts on mollusc biology that are readily available, and there are detailed reviews of groups and individual species of oysters, scallops, mussels, and clams. The reader is referred to these publications at the end of this section for additional information.

Mussels belong to the phylum Mollusca, a group that includes animals as diverse as chitons (chain shells), gastropods, prey shells, cephalopods (cuttlefish and octopus), as well as mussels, oysters, clams, and scallops. The tribe has six classes, one of which is Lamellibranchia or Bivalvia. These animals are laterally compressed, and the soft parts of the body are fully or partially covered by the carapace, which consists of two fins. The gills, or ctenidia, of animals in this class are well-developed organs, specialized for both ingestion and respiration.

2.1.2 External anatomy

The most distinctive feature of mussels are the two shell valves, which may or may not be the same, and may or may not completely encircle the internal soft tissues. They have a variety of shapes and colors, depending on the species. The valves are made mainly of calcium carbonate and have three layers; the inner or pearly layer, the middle or prismatic layer, which forms most of the carapace, and the outer layer or periostacum, a brown leathery layer that is often absent due to abrasion or weathering in older animals.

Figure 6:External and internal characteristics of the shell valves of the hard shell clam,mercenary mercenary. Modified by Cesari and Pellizzari, 1990.

Mussels have no apparent head or tail, but the anatomical terms used to describe these areas in other animals apply to them. The umbo or hinge, where the valves connect, is the dorsal portion of the animal (Figure 6). The opposite region is the abdominal border. In species with prominent siphons (shells), the foot is anteroventral and the siphons posterior (Figure 7). In oysters the anterior region is at the hinge and in scallops where the mouth and rudimentary foot are located.

Figure 7:The internal anatomy of the soft tissues of a mussel of the genusribbons. In this view, the upper gill plates have been removed to reveal the foot and other adjacent tissue. Modified by Cesari and Pellizzato, 1990.

2.1.3 Internal anatomy

By carefully removing one of the shell flaps, the soft tissues of the animals become visible. The differences in the general appearance of an oyster and a scallop can be seen in Figure 8.

Figure 8:The soft tissue anatomy of the European flat oyster,you eat oystersand calico scallop,Argopecten-Gibbus, visible after removing one of the hull valves.I like:COMPARTMENT- adductor muscle;GRAMS- budding;Y- gonads (differentiated aso- ovary andT- testicles in calico scallop);UE- ribbons;METRO- coat andyou-umbo. The inhalation and exhalation chambers of Themantle Cave are identified asCImiFOR EXAMPLEo.

chimney

The soft tissues are covered by the mantle, which consists of two thin-tissue sheaths that thicken at the edges. The two halves of the mantle are attached to the carapace from the hinge ventrally to the paleal line, but are free at their edges. The thickened margins may or may not be pigmented and have three folds. Mantle edge often tentacled; In mussels, the tentacles are at the ends of the siphon. In species such as scallops, the mantle edge has not only rods, but also numerous photosensitive organs - the eyes (Figure 9).

Figure 9:The internal soft tissue anatomy of the hermaphroditic scallop.

The main function of the mantle is to separate the crust, but it also has other purposes. It has a sensory function and can initiate valve closure under unfavorable environmental conditions. You can control the flow of water in the body chamber, and in addition, it has a breathing function. In species such as scallops, it controls the flow of water in and out of the body chamber and therefore the movement of the animal when swimming.

adductor muscle(s)

Removal of the mantle reveals the underlying soft parts of the body, of which the adductor muscles in Dimyarian species (mussels and mussels) or the single muscle in Mononomyarian species (oysters and scallops) are prominent features. In mussels and mussels, the two adductor muscles are located near the anterior and posterior edges of the shell valves. The only large muscle is located in the center of oysters and scallops. The muscles close the valves and counteract the ligament and resilium that open the valves when the muscles relax. In monomyarian species, the divisions of the adductor muscle are clearly seen. The large (striated) front part of the muscle is called the "fast muscle" and contracts to close the valves; The smaller, smoother part known as the "catch muscle" holds the valves in place when they are closed or partially closed. Some species that live buried in the substrate (for example, mussels) need external pressure to keep the valves closed, because when mussels are kept away from the substrate in a tank, the muscles weaken and the valves open.

welling up

Prominent gills or ctenidia are a key feature of the lamellar branches. They are large, leaf-like organs used partly for breathing and partly for filtering food from water. There are two pairs of gills on each side of the body. At the anterior end, two pairs of valves called labial palps surround the mouth and direct food into the mouth.

Afternoon

At the base of the visceral mass is the foot. In species such as mussels, it is a well-developed organ that is used to dig into the substrate and fix the animal in position. It is greatly reduced in scallops and mussels and may have little function in adults, but it is important in the larval and juvenile stages and is used for locomotion. In the case of oysters, a lot. In the center of the foot is the opening of the byssus gland, through which the animal secretes an elastic, thread-like substance called "byssus", which it uses to adhere to a substrate. This is important in species such as mussels and some scallops to allow the animal to anchor itself in position.

digestive system

Large gills filter food from the water and direct it toward the cleft lip that surrounds the mouth. The food is classified and introduced into the mouth. Mussels have the ability to select filtered food from the water. Mucus-bound food boluses that are fed in the mouth are sometimes rejected by the palps and excreted by the animal as so-called "pseudo-feces". A short esophagus runs from the mouth to the stomach, which is a hollow sac with several openings. The stomach is completely surrounded by the digestive diverticulum (gland), a dark mass of tissue often called the "liver." An opening in the stomach leads to the highly bristly intestine, which extends to the foot in mussels and the gonad in scallops, ending in the rectum and finally the anus. Another opening in the stomach leads to a closed bag-like tube containing the crystalline stylet. The stylet is a transparent gelatinous rod that in some species can be up to 8 cm long. It is round at one end and pointed at the other. The rounded end meets the gastric shield in the stomach. It is believed to help mix food in the stomach and release enzymes that aid digestion. The style is made up of layers of mucoproteins that release digestive enzymes to convert starches into digestible sugars. If the mussels are kept out of the water for a few hours, the crystalline style is greatly reduced and may disappear, but is quickly restored when the animal is returned to the water.

cycle

Mussels have a simple circulatory system that is difficult to understand. The heart is found in a transparent sac, the pericardium, close to the adductor muscle in monomyarian species. It consists of two irregularly shaped atria and a ventricle. The anterior and posterior aorta originate from the ventricle and carry blood to all parts of the body. The venous system is a loose series of thin-walled sinuses through which blood returns to the heart.

nervous system

The nervous system is difficult to observe without special preparation. Basically, it consists of three pairs of ganglia with connecting members (cerebral, pedal and visceral ganglia).

sistema urogenital

The sexes of bivalves can be separate (dioecious) or hermaphroditic (monoecious). The gonad may be a prominent and well-defined organ in scallops or occupy the majority of the visceral mass as in mussels. The gonad is usually only visible in oysters during the breeding season, when it can make up to 50% of the body volume. In some species, such as scallops, the sexes can be easily distinguished with the naked eye when the gonad is full, since the malegonada is white and the female red, even in hermaphroditic species. The full color of the gonads can differentiate the sexes in some species, eg bivalves. In other species, a microscopic examination of the gonad is necessary to determine the sex of the animal. A low level of hermaphroditism can occur in dioecious species.

Protandry and sexual inversion can occur in bivalves. In some species, males predominate over smaller animals, suggesting that males develop sexually before females or that some animals develop as males first and then become females as they grow older. In some species, eg. the European flat oyster,you eat oystersthe animal may originally spawn as a male in one season, fill the gonads with eggs, and spawn a second time as a female during the season.

The renal system is difficult to see in some mussels, but it is in species such as scallops where the two kidneys are two small, brown, sac-like bodies that lie flat against the front of the adductor muscle. The kidneys empty into the mantle chamber through large slits. In scallops, eggs and sperm are expelled from the gonads through ducts into the renal lumen and then into the mantle chamber.

2.2 LIFE HISTORY

2.2.1 Shell development and egg formation

In most bivalves, sexual maturity depends on size rather than age, and size at sexual maturity depends on species and geographic distribution. The production of eggs and sperm is called gametogenesis, and the size, temperature, quantity, and quality of the mussel's food are certainly important in initiating this process. The gonad consists of many branching ciliated ducts, from which numerous sacs called follicles open. Gametes are formed by the proliferation of germ cells that line the wall of the follicle. The gonad undergoes continuous development until it reaches full maturity, but this development has been divided into several stages for convenience, e.g. For example, dormant, evolved, mature, partially spawned, and spawned. When the gonadal gonadal tissues are fully mature, they are very distinct and form an important part of the animal's soft tissues. The gonaducts that carry gametes to the body chamber develop, enlarge, and are easily seen in the gonad. At this point, the animal is often said to be mature.

Figure 10:Photomicrographs of histological sections through the scallop ovary,Argopecten-Gibbus, during gametogenesis. to the left (A), developing ovules can be seen in the walls of numerous follicles. The correct photo (B) shows follicles filled with mature oocytes (Courtesy of Cyr Couturier and Samia Sarkis).

Various methods have been used to determine if a mussel is mature and ready to spawn. The most accurate method is to obtain histological slides from the gonads (Figure 10), but this is expensive, time consuming, and the animal must be euthanized. Gonadal smears, or taking small samples of the gonads from a few individuals of a strain and examining them microscopically, is an alternative and most commonly used technique. For scallops, the gonadal index (gonad weight divided by soft tissue weight, multiplied by 100) is sometimes used. In hatcheries, a strict routine is generally followed to condition adults for spawning, and with practice, most hatchery managers quickly develop the ability to tell if an animal is mature and ready to spawn. when macroscopically observing the gonads.

Mussels that reach sexually mature size and spawn for the first time are sometimes referred to as damsels. Although these animals reach sexual maturity, the number of gametes produced is limited and sometimes not all are viable. During subsequent spawning, the number of gametes produced is greatly increased.

The spawning season in natural populations varies by species and geographic location. Spawning can be triggered by a variety of environmental factors, including temperature, chemical and physical stimuli, water currents, or a combination of these and other factors. The presence of sperm in the water usually triggers spawning in other animals of the same species. Some mussel species in tropical environments have adult gametes throughout the year, and limited spawning may occur continuously throughout the year. In temperate zones, spawning is usually restricted to a specific time of the year. Many mussels spawn en masse and the spawning season can be short. Most of the contents of the gonads are briefly released during spawning. Other mussel species have a long spawning season that can last for weeks. These species are sometimes referred to as bargaining pawns. Limited spawning occurs over a long period, with one or two main pulses during this period. In some species there may be more than one distinct spawning in a year. In hermaphroditic species, spawning is timed so that the male or female portion of the gonads reproduces first. This minimizes the possibility of self-pollination.

In most mussel species of commercial interest, the gametes are released into the open environment where fertilization takes place. Semen is released in a thin, steady stream through the exhalation port, or siphon. The release of eggs is more intermittent and they are emitted in the form of clouds through the exhalation orifice or siphon. In species such as scallops or oysters, the females often hit the valves to expel the eggs. This can be done to clean the eggs that are in the gills. After spawning, the gonads of many species are emptied and it is impossible to distinguish the sex macroscopically in individuals. The animal must then be in the resting phase. In dribbling pedestrians, the gonads may never fully empty.

Some bivalves, for example the European flat oyster, are larviparous with the earliest stages of larval development occurring in the inhalation chamber of the oyster's mantle cavity in the female stage. Eggs are passed through the gills when spawning and are retained in the mantle chamber. The sperm is ingested through the inhalation port. The length of time the larvae are kept in the mantle chamber and the length of time the larvae live freely on the surface of the water varies from species to species. In some genres, eg.Tiostrea, the larvae can be part of the plankton for only one day.

Occasionally, especially in temperate areas, spawning may not occur for a few years. This could be the result of several factors, but is probably mainly related to water temperatures that remain too low to trigger spawning. When this occurs in oysters, eggs and sperm can be reabsorbed into gonadal tissue, broken down, and stored as glycogen. In clams and mussels, the gonad may remain mature until the next year.

2.2.2 Embryonic and larval development

These topics are covered in more detail in later sections, but a brief overview is provided here for continuity. Larval development is similar whether initial development takes place in the female's mantle chamber or entirely in the open.

Egg cells undergo meiotic division after fertilization to reduce the number of chromosomes to a haploid number before the male and female pronuclei fuse to form the zygote. Two polar bodies are released during meiotic division and, when visible, indicate successful fertilization. Cell division begins and within 30 minutes after fertilization, the egg cell divides into the two-cell stage. The eggs are heavier than water and sink to the bottom of the tank where cell division continues.

The time required for embryonic and larval development is species-specific and depends on temperature (Figure 11). Within 24 hours, the fertilized ovum progressed through the multicellular stages of blastula and gastrula and became a motile trochophore in 24 to 36 hours. Trochophores are somewhat oval in shape, about 60-80 m in size, and have a row of cilia around the center with an apical flagellum that allows them to swim.

The early larval stage is known as the straight hinge, "D" or prodisoshell stage I. The shell length of the early straight-hinge stage varies by species, but is generally 80–100 m (longer in larval oysters). The larva has two valves, a complete digestive system, and an organ called a velum, which is characteristic of mussel larvae. The veil is circular and may protrude between the valves. It is ciliated on the outer edge and this organ allows the larva to swim, but long enough to remain in the water column. As the larva swims through the water column, the veil collects phytoplankton on which the larva feeds.

The larvae continue to swim, feed, and grow, and within a week develop umbos, which are bumps on the shell near the hinge. As the larvae continue to grow, the umbones become more prominent and the larvae are now in the umbone or prodissoconch II stage. The larvae of the Prodissoconch II stage have varied shapes and with practice it is possible to identify larvae of different bivalve species in the plankton. This has been used by biologists to predict oyster assemblages in the wild for the industry. The length of the larval stage varies depending on the species and environmental factors such as temperature, but can range from 18 to 30 days. Larval maturity size also varies by species and can be 200-330 m.

Figure 11:Representation of the stages of development of the shell of luck,Argopecten-Gibbusthat occur within a hatchery. The length of the period between the different stages is given in hours or days for this specific species and may vary for other mussel species.

As the larvae approach maturity, a foot develops and gill rudiments become visible. In some species, small dark circular spots called eyespots develop near the center of each leaflet. Between swimming periods, the larvae settle and crawl over a substrate with their feet. When a suitable substrate is found, the larva is ready to metamorphose and begin its benthic existence. Mature oyster larvae excrete a small drop of cement from a gland in the foot, turn around, and enter through the left valve. They remain attached to this place for the rest of their lives. In other species, the larva secretes the byssus from the byssal gland of the foot, which serves as a temporary support to adhere to a substrate. The larva is now ready for metamorphosis.

2.2.3 Metamorphosis

Metamorphosis is a critical phase in bivalve evolution, during which the animal changes from a floating planktonic existence to a sedentary benthic existence. Both in the wild and in hatcheries, significant deaths can occur at this time. The subject will be discussed in detail later, since it is an important aspect in the production of hatchery juvenile mussels.

2.2.4 Power

Mussels are filter feeders, feeding mainly on phytoplankton, microscopic plants. In juveniles and adults, the ctenidia or gills are well developed and serve the dual purpose of ingestion and respiration. The ctenidia are covered with cilia, tiny vibrating hairs whose coordinated beat induces a flow of water. When resting on or in a substrate, water enters the animal through the inspiratory port, or siphon, through the gills, and then returns to the surrounding water through the expiratory port, or siphon. The gills collect the plankton and attach it to the mucus. Strings of food-laden mucus are carried by ciliary action along special grooves in the gills to the labial palps, whose function is to help guide food into the mouth. Mussels may exert some food selection, and regularly the friends expel small masses of food, pseudo-feces, which are expelled from the mantle cavity, often by vigorous "tapping" of the shell valves.

It is still largely unknown what constitutes the ideal food for mussels, but phytoplankton undoubtedly make up the bulk of the diet. Other food sources may be important, such as

2.2.5 Growth

Only general statements can be made about growth in juveniles and adults, as it varies by species, geographic distribution, i.e. climate, subtidal or intertidal location, and differences in individuals and their genetic makeup. Growth can also vary greatly from year to year, and there are seasonal growth patterns in temperate zones.

Mussel growth can be measured by a variety of methods, including increasing shell length or height, increasing total or soft body weight, or a combination of all of these factors. In tropical areas, growth can vary seasonally and be faster during or after rainy periods, when nutrients reach the ocean, leading to increased phytoplankton production. In temperate areas, growth is usually rapid in spring and summer, when food is plentiful and water temperatures are warmest. In winter it practically stops, leading to annual bark checks. These winter checks can be used for decrepit mussels. Some species are short-lived, others can live for more than 150 years.

In culture operations, important considerations in mussel culture are the time required to reach sexual maturity and the size of the market. The objective of mussel farming is to grow mussels to marketable size as quickly as possible to make the operation economically attractive.

2.2.6 Deaths

Larvae, juvenile and adult mussels can die from a variety of causes, which may be environmental or biological in origin. The subject is too broad to cover in detail here, but a brief summary is provided to highlight several salient points that may be important in construction operations.

The physical environment can result in severe mussel deaths at all three stages. Excessive temperatures or prolonged cold spells can kill mussels, as can sudden changes in temperature. Severe extreme salinities, particularly low salinities after periods of heavy rain or snowmelt runoff, can also cause numerous deaths. Heavy sedimentation can suffocate and kill adolescents and adults.

Environmental contamination, especially industrial pollution, can cause significant deaths in young and adult mussels. Both industrial and domestic contamination can pose problems for hatcheries and should be avoided. Household contamination can increase organic and bacterial loads in water and contribute to a variety of potentially toxic materials. Little is known about the combined effects of sublethal concentrations of the wide range of man-made organic and organometallic compounds that may be present in such effluents.

Larvae, juvenile and adult mussels are preyed on by a variety of animals that can cause serious fatalities. In the natural environment, plankton eaters are likely to consume large numbers of larvae. In hatcheries, predation is not a problem as the water used is filtered and all predators are removed.

Mussels are hosts to parasites that can cause fatalities, especially in adulthood. clam borers,polishersp., and the sponges burrow into the shells and weaken them, causing deaths.

Probably the main cause of death of mussels, particularly larvae and juveniles in hatcheries, is disease. Considerable research effort has gone into studying mussel diseases and trying to develop methods to control them.

Diseases can be devastating to adult mussels, as evidenced by the extinction of some populations around the world. Some examples are,

dermocistidio:
a fungal disease of mussels caused byPerkinsus marinus;

Delaware Bay Disease (MSX):
a disease caused by haplosporidic protozoa,Haplosporidium (Minchinia) nelsoni;

SSO (shore organism disease):
a disease caused by the haplosporid protozoanHaplosporidium costale, (which together withH.Nelsondecimated large populations of Virginia oysters off the US Atlantic coast and now extending north into Atlantic Canada).

but disease:
disease caused by protozoa,Marteilia refringens;

Bonamiasis (haemocyte disease):
Disease caused by the microcellular parasite,Bonamia Ostreae;
(But the disease and bonamiasis actually led to the disappearance of the European oyster in some parts of Europe.)

Although considerable work has been done on these diseases, no practical methods have been developed to control them and return oyster populations to previous levels. The severity of these diseases indicates the care required when transporting adult mussels to a hatchery.

Diseases that occur in hatcheries appear to be caused by bacteria rather than protozoa. Bacteria are present to some extent in algal and larval cultures. In fact, bacteria can form an important part of the diet of the larvae. Periodically, however, large groups of larvae suddenly die and an entire crop is lost. High bacterial counts are almost always associated with these large-scale deaths. The bacteria may cause death (pathogenic) or may simply be present as opportunistic bacteria (saprophytes) that feed on the dying larvae. Disease-causing bacteria belong mainly to the genusvibriosp. and all precautions must be taken to prevent them from causing epidemics in hatcheries. The best way to prevent such outbreaks is to follow strict hygiene procedures and ensure that the larvae are well fed with good quality food. The larvae must be checked regularly. If disease occurs or is suspected, tanks and equipment should be disinfected with a bleach solution and rinsed thoroughly with fresh water. To protect the larvae from further contamination, the tanks should be recharged with ultraviolet radiation or ozone-treated seawater. The hatchery practically dispenses antibiotics to fight disease. They are expensive and add to operating costs, and there is also the fear that an antibiotic-resistant strain of bacteria will develop, which could lead to even more serious disease problems in the future.

2.3 RECOMMENDED READING

Balouet, G., Poder, M. & Cahout, A.1983. Hemocytic parasitosis: morphology and pathology of lesions in the French flat oyster,you eat oystersL. Aquaculture34: 1 - 14

Bower, SM1992. Diseases and parasites of mussels. In: The MusselMytilo: ecology, physiology, genetics and culture. E. G. Gosling (ed.). Elsevier. Development of aquaculture fish. Science.25: 465-510

Bower, SM, McGladdery, SE y precio, I. M.1994. Synopsis of infectious diseases and parasites of commercially exploited shellfish. Annual. Rev. of Pisces. Diseases. Elsevier,4: 1 - 199

Cesari, P. and Pellizzato, M.1990. It's Biologyphilippine gangs, S. 21-46. Me:philippine gangs: Biology and Experimentation. Veneto Region, Agricultural Development Agency, Venice: 299 pages (text in Italian and English)

Elston, R. A.1990. Molluscan diseases; Shellfish Guide. Washington Sea Concession. University of Washington, United States. SH179.S5E44: 73 p.

Ford, SE y Tripp, M.R.1996. Diseases and Defense Mechanisms. In: The Oriental Oyster,Crassostrea virginica. . . . . . . . . . . . . . . . against Kennedy, R.I.E. Newell and Ebel AF (eds.). Maryland Sea Grant, University. Maryland, College Park, Maryland, USA. ISBN-0-943-676-61-4: 423 -

Ford, SE2001. Pests, parasites, diseases and defense mechanisms of hard molluscs,mercenary mercenary. In: Biology of the hard clam, J.N. Kraeuter and M. Castagna (eds.). Elsevier. Development of AquacultureFish. Science.31: 591 - 628

Getchell, R. G.1991. Diseases and parasites of the scallop. In: Scallops: Biology, Ecology and Aquaculture. SE Shumway (ed.). Elsevier. Development of aquaculture fish. Science.21: 471-494

Gosling, E. (Hrsg.).1992. To Shell,Mytilo: ecology, phytology, genetics and culture. Elsevier. Development of aquaculture Fish.Sci.25: 589 s.

Gosling, E.2002. Mussels, Biology, Ecology and Culture. Books of fishing news. Blackwell Publishing, UK: 443 p.

Grizel , H. , Miahle , E. , Chagot , D. , Buolo , V. & Bachere , E. .1988. Bonamiasis: a model disease study in marine molluscs. In: Disease processes in marine bivalve molluscs W.S. Fischer (Hrsg.). Amer. Fisch.Soc. Spez. publ.18. Bethesda Maryland: 1-4

Jorgensen, C. B.1990. Seepage of mussels: hydrodynamics, bioenergetics, physiology and ecology. Olsen and Olsen, Fredensborg, Denmark: 140 pp.

Kennedy, VX, Newell, RIE & Eble, A.F. (Eds.).1996. An Oriental OysterCrassostrea virginica. . . . Maryland Sea Grant, University. Maryland, Hochschulpark, Maryland, USA. ISBN-0-943-676-61-4: 734 p.

Joker, p.1976. Creation of the flat oyster genusoysters. Elsevier. Development of aquaculture fish. Science.3: 238 s.

Kraeuter, J.N. and Castagna, M. (Eds.).2001. Biology of the Dura Clam. Elsevier. Development of aquaculture fish. Science.51: 751 s.

MANZI, J. J. and Castanha, M.1989. Mariculture of clams in North America. Elsevier. Aquaculture and fisheries development. Science.19: 461 s.

Moro, J.1983. Scallop and queen fisheries in the British Isles. Fishing News Books Ltd, Surrey, UK: 143 S.

Morton, J. E.1960. Mollusks: Introduction to their form and function. Harper Textbooks, New York, USA: 232 pages.

Quayle, D. G.1988b. Pacific oyster farming in British Columbia. Could. Bull. Fish. Aquatic Sciences.218: 241 s.

Shumway, SE (Reg.).1991. Scallops, Biology, Ecology and Aquaculture. Elsevier. Development in Fishery Aquaculture. Science.21: 1095 S.

Yonge, C. M. y Thompson, T. E.1976. Live marine molluscs. Will Collins, Sons and Co. Ltd, Glasgow: 288 pp.