Rotifers are microscopic aquatic animals of the phylum Rotifera. Rotifers can be found in many freshwater environments and in moist soil, where they inhabit the thin films of water that are formed around soil particles.
Origin of the Lateral Line System
Lateral line is a canal along the side of a fish containing pores that open into tubes supplied with sense organs sensitive to low vibrations.
Robert H. Denison explained the origin of the lateral line system. He explained that early vertebrates had a pore-canal system in the dermis which functioned as a primitive sensory system in detecting water movement.
Through the evidences from fossils, embryology and comparative anatomy, Denison (1966) established that the inner ear is closely related to the lateral line system. He found a distinct relationship between the pore canal system and the lateral line in Osteotraci.
The inner ear and the lateral line are developed from ectodermal thickenings, called dorso-lateral placodes. These have a number of similarities, including receptors with sensory hairs, and are both innervated by fibers in the acoustico-lateral area of the brain.
The pore canal system is present and developed in Osteostraci (ostracoderm).
It is also present in Heterostraci which is another group of ostracoderms and includes early vertebrates such as lungfishes and crossopterygians.
As its presence is extensive, it is reasonable to suggest that the pore canal system was a primitive character in early vertebrates .
In transverse sections also , it is very difficult to differentiate the pore canal system from a lateral line canal.
Structure of the Lateral Line System
Epidermal structures called neuromasts form the peripheral area of the lateral line.
Neuromasts consist of two types of cells, hair cells and supporting cells.
Hair cells have an epidermal origin and each hair cell has one high kynocyle (5-10 μm) and 30 to 150 short stereocilia (2-3 μm).
The number of hair cells in each neuromast depends on its size, and they can range from dozens to thousands.
Hair cells can be oriented in two opposite directions with each hair cell surrounded by supporting cells.
At the basal part of each hair cell, there are synaptic contacts with afferent and efferent nerve fibers. Afferent fibers, transmit signals to the neural centres of the lateral line and expand at the neuromast base. The regulation of hair cells is achieved by the action of efferent fibers.
Stereocilia and kinocilium of hair cells are immersed into a cupula and are located above the surface of the sensory epithelium.
The cupula is created by a gel-like media, which is secreted by non-receptor cells of the neuromast.
Fishes, amphibians, reptiles, and birds have paired pharyngeal ultimobranchial glands that secrete the hypocalcemic hormone calcitonin. The corpuscles of Stannius, unique glandular islets found only in the kidneys of bony fishes, secrete a peptide called hypocalcin.
Origin of the Lateral Line System
Lateral line is a canal along the side of a fish containing pores that open into tubes supplied with sense organs sensitive to low vibrations.
Robert H. Denison explained the origin of the lateral line system. He explained that early vertebrates had a pore-canal system in the dermis which functioned as a primitive sensory system in detecting water movement.
Through the evidences from fossils, embryology and comparative anatomy, Denison (1966) established that the inner ear is closely related to the lateral line system. He found a distinct relationship between the pore canal system and the lateral line in Osteotraci.
The inner ear and the lateral line are developed from ectodermal thickenings, called dorso-lateral placodes. These have a number of similarities, including receptors with sensory hairs, and are both innervated by fibers in the acoustico-lateral area of the brain.
The pore canal system is present and developed in Osteostraci (ostracoderm).
It is also present in Heterostraci which is another group of ostracoderms and includes early vertebrates such as lungfishes and crossopterygians.
As its presence is extensive, it is reasonable to suggest that the pore canal system was a primitive character in early vertebrates .
In transverse sections also , it is very difficult to differentiate the pore canal system from a lateral line canal.
Structure of the Lateral Line System
Epidermal structures called neuromasts form the peripheral area of the lateral line.
Neuromasts consist of two types of cells, hair cells and supporting cells.
Hair cells have an epidermal origin and each hair cell has one high kynocyle (5-10 μm) and 30 to 150 short stereocilia (2-3 μm).
The number of hair cells in each neuromast depends on its size, and they can range from dozens to thousands.
Hair cells can be oriented in two opposite directions with each hair cell surrounded by supporting cells.
At the basal part of each hair cell, there are synaptic contacts with afferent and efferent nerve fibers. Afferent fibers, transmit signals to the neural centres of the lateral line and expand at the neuromast base. The regulation of hair cells is achieved by the action of efferent fibers.
Stereocilia and kinocilium of hair cells are immersed into a cupula and are located above the surface of the sensory epithelium.
The cupula is created by a gel-like media, which is secreted by non-receptor cells of the neuromast.
Fishes, amphibians, reptiles, and birds have paired pharyngeal ultimobranchial glands that secrete the hypocalcemic hormone calcitonin. The corpuscles of Stannius, unique glandular islets found only in the kidneys of bony fishes, secrete a peptide called hypocalcin.
Osmoregulation is the process of maintaining salt and water balance (osmotic balance) across membranes within the body. The fluids inside and surrounding cells are composed of water, electrolytes, and nonelectrolytes. An electrolyte is a compound that dissociates into ions when dissolved in water.
Introduction
Ostracoderms (shell-skinned) are of several groups of extinct, primitive, jawless fishes that were covered in an armour of bony plates.
They appeared in the Cambrian, about 510 million years ago, and became extinct towards the end of the Devonian, about 377 million years ago. They were quite abundant during the upper Silurian and Devonian periods. Most of fossils of Ostracodermi were preserved in the bottom sediments of freshwater streams.
However, the opinion is sharply divided as to whether their habitat was freshwater or marine.
The first fossil fishes that were discovered were ostracoderms.
The Swiss anatomist Louis Agassiz received some fossils of bony armored fish from Scotland in the 1830s.
The ostracoderms resembled the present day cyclostomes (lampreys and hagfishes) in many respects and together with them constitute a special group of jawless vertebrates, the Agnatha.
Characteristics: They use gills exclusively for respiration but not for feeding . Earlier chordates with gills used them for both respiration and feeding. Ostracoderms had separate pharyngeal gill pouches along the side of the head, which were permanently open with no protective operculum. mostly small to medium-sized fishes, protected by a heavy, bony dermal (derived from skin) armor. bottom-dwellers; filter-feeders or grazers. no paired fins, but many with stabilizing paired flaps on either side of head.
(1) Ostracoderms were the first vertebrates.
(2) They were popularly called armoured fishes.
(4) They lived in freshwater.
(5) They were bottom dwellers.
(6) Their body was fish-like and did not exceed 30 cm in size.
(7) Paired fins were absent.
(8) Median and caudal fins were present.
(9) The caudal fin was of heterocercal type.
(10) The head and thorax were covered by heavy armour of bones. It protected ostracoderms from the giant scorpion like arthropods, eurypterids.
(11) Bony skull was well developed.
(12) Mouth was mostly present on the ventral side.
(13) They were having large number of gill slits.
(14) The nervous system had 10 pairs of cranial nerves.
(15) The head had a pair of lateral eyes, and a median pineal eye.
(16) They were filter feeders, feeding like a vacuum cleaner.
(17) The endoskeleton was either bony or cartilaginous.
Digestive physiology of herbivorous fishMahendra Pal
The knowledge of food and feeding habits and the physiology of digestion of any organism is most essential for development of artificial feed in culture practices. Fish and shellfish belong to the poikilothermous animal. The digestion process is somewhat different than the terrestrial animals. Similarly the mechanism of digestion and absorption process is quite different in fishes and shellfishes. The basic function of digestive system is to dissolve foods by rendering them soluble so that they can be absorbed and utilized in the metabolic process. The system may also function to remove dangerous toxic properties of certain food substances.
Fish generally change their feeding habits depending upon availability of food. So according to their feeding fishes are classified into different categories viz., predators, grazers, strainers, suckers and parasites.
Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres. Fish usually migrate to feed or to reproduce, but in other cases the reasons are unclear.
Migrations involve the fish moving from one part of a water body to another on a regular basis. Some particular types of migration are anadromous, in which adult fish live in the sea and migrate into fresh water to spawn, and catadromous, in which adult fish live in fresh water and migrate into salt water to spawn.
Marine forage fish often make large migrations between their spawning, feeding and nursery grounds. Movements are associated with ocean currents and with the availability of food in different areas at different times of year. The migratory movements may partly be linked to the fact that the fish cannot identify their own offspring and moving in this way prevents cannibalism. Some species have been described by the United Nations Convention on the Law of the Sea as highly migratory species. These are large pelagic fish that move in and out of the exclusive economic zones of different nations, and these are covered differently in the treaty from other fish.
Salmon and striped bass are well-known anadromous fish, and freshwater eels are catadromous fish that make large migrations. The bull shark is a euryhaline species that moves at will from fresh to salt water, and many marine fish make a diel vertical migration, rising to the surface to feed at night and sinking to lower layers of the ocean by day. Some fish such as tuna move to the north and south at different times of year following temperature gradients. The patterns of migration are of great interest to the fishing industry. Movements of fish in fresh water also occur; often the fish swim upriver to spawn, and these traditional movements are increasingly being disrupted by the building of dams.
Its related with the stream of Biology .
This is all about the Cartilaginous fish - easy explanation and classification.
Also include fundamental characterstics of Pisces
Which is a class of Superclass Pisces.
Osmoregulation is the process of maintaining salt and water balance (osmotic balance) across membranes within the body. The fluids inside and surrounding cells are composed of water, electrolytes, and nonelectrolytes. An electrolyte is a compound that dissociates into ions when dissolved in water.
Introduction
Ostracoderms (shell-skinned) are of several groups of extinct, primitive, jawless fishes that were covered in an armour of bony plates.
They appeared in the Cambrian, about 510 million years ago, and became extinct towards the end of the Devonian, about 377 million years ago. They were quite abundant during the upper Silurian and Devonian periods. Most of fossils of Ostracodermi were preserved in the bottom sediments of freshwater streams.
However, the opinion is sharply divided as to whether their habitat was freshwater or marine.
The first fossil fishes that were discovered were ostracoderms.
The Swiss anatomist Louis Agassiz received some fossils of bony armored fish from Scotland in the 1830s.
The ostracoderms resembled the present day cyclostomes (lampreys and hagfishes) in many respects and together with them constitute a special group of jawless vertebrates, the Agnatha.
Characteristics: They use gills exclusively for respiration but not for feeding . Earlier chordates with gills used them for both respiration and feeding. Ostracoderms had separate pharyngeal gill pouches along the side of the head, which were permanently open with no protective operculum. mostly small to medium-sized fishes, protected by a heavy, bony dermal (derived from skin) armor. bottom-dwellers; filter-feeders or grazers. no paired fins, but many with stabilizing paired flaps on either side of head.
(1) Ostracoderms were the first vertebrates.
(2) They were popularly called armoured fishes.
(4) They lived in freshwater.
(5) They were bottom dwellers.
(6) Their body was fish-like and did not exceed 30 cm in size.
(7) Paired fins were absent.
(8) Median and caudal fins were present.
(9) The caudal fin was of heterocercal type.
(10) The head and thorax were covered by heavy armour of bones. It protected ostracoderms from the giant scorpion like arthropods, eurypterids.
(11) Bony skull was well developed.
(12) Mouth was mostly present on the ventral side.
(13) They were having large number of gill slits.
(14) The nervous system had 10 pairs of cranial nerves.
(15) The head had a pair of lateral eyes, and a median pineal eye.
(16) They were filter feeders, feeding like a vacuum cleaner.
(17) The endoskeleton was either bony or cartilaginous.
Digestive physiology of herbivorous fishMahendra Pal
The knowledge of food and feeding habits and the physiology of digestion of any organism is most essential for development of artificial feed in culture practices. Fish and shellfish belong to the poikilothermous animal. The digestion process is somewhat different than the terrestrial animals. Similarly the mechanism of digestion and absorption process is quite different in fishes and shellfishes. The basic function of digestive system is to dissolve foods by rendering them soluble so that they can be absorbed and utilized in the metabolic process. The system may also function to remove dangerous toxic properties of certain food substances.
Fish generally change their feeding habits depending upon availability of food. So according to their feeding fishes are classified into different categories viz., predators, grazers, strainers, suckers and parasites.
Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres. Fish usually migrate to feed or to reproduce, but in other cases the reasons are unclear.
Migrations involve the fish moving from one part of a water body to another on a regular basis. Some particular types of migration are anadromous, in which adult fish live in the sea and migrate into fresh water to spawn, and catadromous, in which adult fish live in fresh water and migrate into salt water to spawn.
Marine forage fish often make large migrations between their spawning, feeding and nursery grounds. Movements are associated with ocean currents and with the availability of food in different areas at different times of year. The migratory movements may partly be linked to the fact that the fish cannot identify their own offspring and moving in this way prevents cannibalism. Some species have been described by the United Nations Convention on the Law of the Sea as highly migratory species. These are large pelagic fish that move in and out of the exclusive economic zones of different nations, and these are covered differently in the treaty from other fish.
Salmon and striped bass are well-known anadromous fish, and freshwater eels are catadromous fish that make large migrations. The bull shark is a euryhaline species that moves at will from fresh to salt water, and many marine fish make a diel vertical migration, rising to the surface to feed at night and sinking to lower layers of the ocean by day. Some fish such as tuna move to the north and south at different times of year following temperature gradients. The patterns of migration are of great interest to the fishing industry. Movements of fish in fresh water also occur; often the fish swim upriver to spawn, and these traditional movements are increasingly being disrupted by the building of dams.
Its related with the stream of Biology .
This is all about the Cartilaginous fish - easy explanation and classification.
Also include fundamental characterstics of Pisces
Which is a class of Superclass Pisces.
Macrobrachium rosenbergii , also known as the giant river prawn or giant freshwater prawn, is a commercially important species of palaemonid freshwater prawn. It is found throughout the tropical and subtropical areas of the Indo-Pacific region.
Life cycle of Protozoan parasite
fish parasite
parasitologyClinostomum compalanatum and Clinostomum marginatum are unsegmented flatworms of the class Trematoda and the order Digenea.
They are also called as yellow grub
They occur frequently in the skin and the muscle of the freshwater fish.
Small cream coloured nodules or cysts ranging from pinhead size up to 2.5 mm depending on their age
The number of cysts may vary from 1-100 or more than
They have an oval or round shape.
The skin of the fish in reaction to the infection produces the cysts, which contain worms.
It may take 3 weeks to make clearly visible cysts after the infection and 7 weeks to reach full size
Parasitism:
It is defined as an intimate and obligatory relationships between two heterospecific organisms during which the parasite, usually the smaller of the two partners is metabolically depended on the host.
Parasitology:
The term ‘parasitology’ is originated from Greek word- ‘Para’ means beside, ‘sitos’ means food and ‘logus’ means study.
It is the branch of science which deals with the study of the relationship between the parasite and host. This discipline includes several approaches to the study of parasitic organisms such as phylogeny, morphology, ecology, life history, physiology, chaemotherapy, serology, immunology and bio chemistry.
Fish parasitology:
It is the branch of science that deals with the study of parasite of fishes. It includes the infection and disease of fish caused by parasite.
PRINCIPLE 1: Sustainable fish stock
A fishery must be conducted in a manner that does not lead to over-fishing or depletion of the exploited populations and, for those populations that are depleted, the fishery must be conducted in a manner that demonstrably leads to their recovery
PRINCIPLE 2: Minimizing environmental effect
Fishing operations should allow for the maintenance of the structure, productivity, function and diversity of the ecosystem (including habitat and associated dependent and ecologically related species) on which the fishery depends.
Fishing ground is those area of a water body where fish concentration remain always significant
Generally fishing ground is divided into two ways- permanent fishing ground and temporary fishing ground. Bay of Bengal has four fishing ground.
Fish location is the phenomenon of locating fish in the sea at a given area.
It also an indirect method where fishes are detected/found not directly detection the fish themselves but by some other factors like water temperature, turbidity, food availability etc.
Traps are fishing devices into which fish or shellfish are enticed by bait or shelter spaces or enclosures where they are guided to enter, because of an obstacle placed in their normal migration path and from which their escape is made difficult by constriction, retarding valves or labyrinths.
Trap fishing is a passive fishing technique of ancient origin. There is extraordinary variety in their design, fabrication and operation.
The grass carp (Ctenopharyngodon idella) is the species of fish with the largest reported production in aquaculture globally, over five million tonnes per year. It is a large herbivorous freshwater fish species of the family Cyprinidae
Zooplankton distribution and seasonal successionAl Nahian Avro
The seasonal distribution of the major components of the zooplankton community, protozooplankton, copepods and cladocerans, along a eutrophication gradient were examined in order to establish if eutrophication through increases in phytoplankton biomass and productivity has an impact on biomass and composition of the zooplankton community
The Estuarine System consists of deepwater tidal habitats and adjacent tidal wetlands that are usually semienclosed by land but have open, partly obstructed, or sporadic access to the open ocean, and in which ocean water is at least occasionally diluted by freshwater runoff from the land. The salinity may be periodically increased above that of the open ocean by evaporation. Along some low-energy coastlines there is appreciable dilution of sea water. Offshore areas with typical estuarine plants and animals, such as red mangroves (Rhizophora mangle) and eastern oysters (Crassostrea virginica), are also included in the Estuarine System.
Basic bioeconomics model of fishing. In order to perform estimations and predictions of the bioeconomic impact derived from different management strategies, a dynamic modelling approach of the resource and the fishery as a whole is needed. In this Secetion we develop : (1) the static and dynamic versions of the Gordon-Schaefer (Gordon, 1953, 1954) model; (2) a distributed-delays fleet dynamics model based on Smith's (1969) model; (3) yield-mortality models; and (4) age-structured dynamic models (Seijo & Defeo, 1994a).
The plankton is divisible into two main groups, the phytoplankton and the zooplankton. The primary productivity which we discussed in chapter 10 is primarily the functional aspect of phytoplankton - the other chlorophyll bearing organisms are also to be included, but in most water bodies such as the culture pond an index of primary productivity could be obtained by the mass or number of phytoplankton in a unit volume of water
Chemical Oceanography is fundamentally interdisciplinary. The chemistry of the ocean is closely tied to ocean circulation, climate, the plants and animals that live in the ocean, and the exchange of material with the atmosphere, cryosphere, continents, and mantle
Biological and chemical oceanography.Chemical Oceanography is fundamentally interdisciplinary. The chemistry of the ocean is closely tied to ocean circulation, climate, the plants and animals that live in the ocean, and the exchange of material with the atmosphere, cryosphere, continents, and mantle
The bighead carp is a species of freshwater fish, one of several Asian carps. It is one of the most intensively exploited fishes in aquaculture, with an annual worldwide production of over three million tonnes in 2013, principally from China.
Surimi is a Japanese word that literally means "ground meat". 2. To make surimi, the lean meat from white fleshed fish such as pollock is pulverized into a thick paste. The gelatinous paste can then be combined with various additives to become fake crab, fake lobster, and whatnot.
Students, digital devices and success - Andreas Schleicher - 27 May 2024..pptxEduSkills OECD
Andreas Schleicher presents at the OECD webinar ‘Digital devices in schools: detrimental distraction or secret to success?’ on 27 May 2024. The presentation was based on findings from PISA 2022 results and the webinar helped launch the PISA in Focus ‘Managing screen time: How to protect and equip students against distraction’ https://www.oecd-ilibrary.org/education/managing-screen-time_7c225af4-en and the OECD Education Policy Perspective ‘Students, digital devices and success’ can be found here - https://oe.cd/il/5yV
Instructions for Submissions thorugh G- Classroom.pptxJheel Barad
This presentation provides a briefing on how to upload submissions and documents in Google Classroom. It was prepared as part of an orientation for new Sainik School in-service teacher trainees. As a training officer, my goal is to ensure that you are comfortable and proficient with this essential tool for managing assignments and fostering student engagement.
The Roman Empire A Historical Colossus.pdfkaushalkr1407
The Roman Empire, a vast and enduring power, stands as one of history's most remarkable civilizations, leaving an indelible imprint on the world. It emerged from the Roman Republic, transitioning into an imperial powerhouse under the leadership of Augustus Caesar in 27 BCE. This transformation marked the beginning of an era defined by unprecedented territorial expansion, architectural marvels, and profound cultural influence.
The empire's roots lie in the city of Rome, founded, according to legend, by Romulus in 753 BCE. Over centuries, Rome evolved from a small settlement to a formidable republic, characterized by a complex political system with elected officials and checks on power. However, internal strife, class conflicts, and military ambitions paved the way for the end of the Republic. Julius Caesar’s dictatorship and subsequent assassination in 44 BCE created a power vacuum, leading to a civil war. Octavian, later Augustus, emerged victorious, heralding the Roman Empire’s birth.
Under Augustus, the empire experienced the Pax Romana, a 200-year period of relative peace and stability. Augustus reformed the military, established efficient administrative systems, and initiated grand construction projects. The empire's borders expanded, encompassing territories from Britain to Egypt and from Spain to the Euphrates. Roman legions, renowned for their discipline and engineering prowess, secured and maintained these vast territories, building roads, fortifications, and cities that facilitated control and integration.
The Roman Empire’s society was hierarchical, with a rigid class system. At the top were the patricians, wealthy elites who held significant political power. Below them were the plebeians, free citizens with limited political influence, and the vast numbers of slaves who formed the backbone of the economy. The family unit was central, governed by the paterfamilias, the male head who held absolute authority.
Culturally, the Romans were eclectic, absorbing and adapting elements from the civilizations they encountered, particularly the Greeks. Roman art, literature, and philosophy reflected this synthesis, creating a rich cultural tapestry. Latin, the Roman language, became the lingua franca of the Western world, influencing numerous modern languages.
Roman architecture and engineering achievements were monumental. They perfected the arch, vault, and dome, constructing enduring structures like the Colosseum, Pantheon, and aqueducts. These engineering marvels not only showcased Roman ingenuity but also served practical purposes, from public entertainment to water supply.
How to Split Bills in the Odoo 17 POS ModuleCeline George
Bills have a main role in point of sale procedure. It will help to track sales, handling payments and giving receipts to customers. Bill splitting also has an important role in POS. For example, If some friends come together for dinner and if they want to divide the bill then it is possible by POS bill splitting. This slide will show how to split bills in odoo 17 POS.
Palestine last event orientationfvgnh .pptxRaedMohamed3
An EFL lesson about the current events in Palestine. It is intended to be for intermediate students who wish to increase their listening skills through a short lesson in power point.
How to Create Map Views in the Odoo 17 ERPCeline George
The map views are useful for providing a geographical representation of data. They allow users to visualize and analyze the data in a more intuitive manner.
Operation “Blue Star” is the only event in the history of Independent India where the state went into war with its own people. Even after about 40 years it is not clear if it was culmination of states anger over people of the region, a political game of power or start of dictatorial chapter in the democratic setup.
The people of Punjab felt alienated from main stream due to denial of their just demands during a long democratic struggle since independence. As it happen all over the word, it led to militant struggle with great loss of lives of military, police and civilian personnel. Killing of Indira Gandhi and massacre of innocent Sikhs in Delhi and other India cities was also associated with this movement.
2. Rotifer
The rotifers are microscopic, mostly free-living.
90% of rotifers inhabit freshwater habitats but some
also live in brackish water and a few in the ocean or on
land in damp sites.
Rotifers are used as suitable live food organism for the
early larval stages of marine fish, shrimps and crabs
Rotifers are widely used as food in shrimp and crab
hatcheries for their small size and slow swimming
velocity for the fish larvae that have just resorbed their
yolk sac but cannnot yet ingest the brine shrimp
3. Colouration:
Usually they are transparent and colourless.
The enclosing cuticle may be impart a slight yellowish color
Shape and size:
Range from 0.04 to 2 mm in length and most of them do
not exceed 0.5 mm
The body is bilaterally symmetrical but extremely variable
in shape.
It may be slender and worm-like, broad, flattened or even
spherical
Males have reduced size and are less developed than
females
4. Structure
Its body has a fixed number of about 1000 cells and the growth is not by cell
division but by growth of cytoplasm.
The epidermis of body of rotifers contains a densely packed layer of keratin-like
proteins which is called lorica
The rotifer’s body is divisble into three distnict parts-head, trunk and foot
a) Head:
It may be narrow or lobed but it is typically broad and truncate or slightly convex
It carries the rotatory organ or corona whichis surrounded by a double ciliated
ring, the velum, made of an outer ciliary band or cingulum and anninner ciliary
band or trochus.
Their cilia beat in a circular manner, one clockwise and the other anticlockwise
and look like two wheels spinning, hence the name ‘Rotifera’.
The whirling water movement produced by beating of cilia helps in locomotion,
ingestion of small food particles like algae and detritus, drawing water currents
containing oxygen and food towards mouth and carrying off wastes.
Eyes are apearing as red flecks, occur singly or paired in the brain, as lateral
paired eyes in or near the corona.
The mouth is located in the corona in the midventral line of the head
5. b) Trunk:
The trunk may be cylindrical or variously flattened and broadened.
It is the middle, elongated region between the three region, containing the
chief visceral organs.
It is frequently enclosed in a shell-like transparent, flexible, cuticular
covering called lorica
Lorica is used for the protection, support etc.
They possess a characteristic pharynx (mastax) having 7 numbers of hard
cuticular pieces or trophi in the inner wall which are named as unpaired
‘fulcrum’, paired ‘rami’ and paired ‘unci’.
The excretory system consists of protonephridia which opens posteriorly
into urinary bladder.
The anus is found in the mid-dorsal line at or near the boundary of the
trunk and foot.
6. c) Foot:
The body may taper gradually into the foot.
It may be short or long cylindrical tail-like region.
The foot has one or four mvable finger-like projectons at or near its
end known as toes.
The toes may be short, conical or slender or spine-like.
Foot helps in locomotion i.e. clinging to objects in creeping types
and act as a rudder in swimming types
Foot is modified into long stalk in sessile types
Toes used in holding the substratum while creeping
The pedal glands are commonly located in the foot which secrete an
adhesive material used for permanent attachment or in creeping.
7.
8. Feeding
The favoured food for rotifers are microalgae such as
chlorella, bacteria and yeast.
The whirling water movement produced by beating of cilia
helps in feeding of rotifer.
The digestive tract includes mouth, pharynx, oesophagus,
stomach, intestine, cloaca and digestive gland
Digestion takes place in the stomach and absorption in the
stomach and intestine.
The solution of digested food go to the fluid content of the
pseudocoel and reaches all the parts of the tiny body
9. Reproduction
They are bisexual
Males are usually smaller than the female.
Male exhibits reduced digestive system with loss of cloaca and anus.
They are also differ in the form of lorica, corona and lack of urinary
bladder.
Some rotifers have no distinct corona. Corona is being replaced by simple
ciliated anterior end.
Males are entirely absent in some sub-order of rotifer. Reproduction
occur by parthenogenesis.
Female reproduction system consists of a syncitical ovary and a syncitical
vitellarium bound in a membrane and opening into cloaca by a tubular
oviduct.
Male has a testis which leads into sperm duct and opens out by a genital
pore.
There are two categories of females such as amictic and mictic.
There are no anatomic distinctions between the two female.
10. Amictic female lay ‘amictic eggs’- eggs that give off only one polar body
and hence are diploid.
Mictic female lay ‘mictic eggs’- eggs that give off 2 polar body and hence
are haploid.
The eggs of amictic females undergo parthenogenetic development
If the eggs of mictic females undergo parthenogenetic development; it
develops into male.
If the eggs of mictic females are fertilized by males, a thick resistant shells
are secreted by its and surround the eggs .
These eggs are remain dormant for several days or mounths and can
survive in drought or in unfavourable conditions.
So the asexual phase of amictic females is the common way of
reproduction under favorable conditions and sexual phase is only for
producing dormant eggs under unfavorable conditions
Sperms of males are two types-
a) ‘Typical’ with rounded or oval head and a tail
b) ‘Atypical’ having rod shaped bodies
11.
12. Growth patterns of rotifers
The life span of a rotifer depends on temperature.
At 25°C, the life span is 7 days.
At this temperature, the larva becomes adult within 0.5-1.5 days.
Then the female starts laying eggs once in every four hours.
One female lay about 20 eggs during its lifetime.
Growth and multiplication of rotifers in culture conditions can be divided into four
phases-
Lag phase or induction phase:
When a rotifer is inoculated into a fresh culture medium, it takes a few hours to acclimatise
to the new environment. The reproduction does not occur in this phase, only rotifers may
increase in size.
Log phase or Exponential phase:
Once the rotifers are acclimatised to the new environment, they start to reproduce. They
reproduce very fast and exponential growth is seen.
Transitional or declining phase:
In this phase, the growth rate slows down, egg bearing rotifers become rearer.
Decline phase:
In this phase, only old rotifers without eggs are found.
13. Culture of Rotifers
The culture system of rotifers have 3 units-
a) Unit for culturing the food organisms for rotifer
b) Unit for rotifer stock culture
c) Unit for rotifer mass culture
Brachionus calyciflorus and Brachionus rubens are the most commonly cultured rotifers
in freshwater
• Temperature-15-31°C
• Synthetic medium-
96mg NaHCo3
60mg CaSo4.2H2O
60mg MgSo4
4mg KCl
1L deionized water
• Optimal pH – 6-8 at 25°C
• Minimum oxygen level-1.2mgl-1
• Free ammonia levels-3-5mgl-1 inhibit reproduction
14. Stock culture of rotifers
Filtering the waterbody using a filter of mesh size 50-100 mm pores
Collection of rotifers using a dropper
Take the rotifer in a cavity block containing 3.5 ml distilled/ tap water
Introduce one rotifer into the chorella medium and cover it and keep in diffused light
Replace the medium with fresh chorella-1 million cells/ml at every 12 hour intervals
Separate the rotifers from medium
A small part is used for the maintenance of the stock and the remaining rotifers used
for the upscaling
15. Upscaling of stock cultures
Rotifers are stocked in erlenmeyers at 50 in./ml at 15-30°C with
400ml freshly harvested algae
Rotifer concentration become 200/ml within 3 days
Separate the rotifers using 2 filter screens
Distribution of rotifers in several 15 l bottles filled with 2l water at a density of 50/ml
Supply the fresh algae daily in bottles
After one week, 15l bottles are completely full and used for inoculation of mass
culture
