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Generally fishes restrict their movements within small territorial limits and do not go out of their home ranges. However, a few species travel long distances moving from fresh to sea water or vice versa. This movement of a very large number of fishes for the purpose of feeding of spawning, is know as migration. It may take place in vertical direction, as from the deeper to the surface water, or it may be in horizontal direction, either upstream or down stream. Heape (1931) has defined migration as “a class of movement which impels migrants to return to the region from which they have migrated”. Migration is of the following types:

(a) Alimental migration: This is in search of food and water.

(b) Gametic migration: For reproduction.

(c) Climatic migration: This is to secure more suitable climatic conditions.

(d) Osmoregulatory migration.

The really interesting migrations of mature adult fish are for spawning and feeding. They breed in one area but grow and feed in another area. Examples of such migratory fishes are :

1. Cod (Gadus morhua)

2. Herring (Clupea harengus)

3. Salmon (Salmo sp.)

4. Eel (Anguilla anguilla)

5. Plaice (Pleuronectes platessa)

6. Hilsa (Hilsa ilisha)

Preparation for microscopic study

Objects to be studied under a microscope need preparation. If the object is small enough, through light can pass, and the study in finest details is not required a whole mount preparation will be sufficient. In case of large objects they are to be cut in thin sections for the study. This is called histological preparation.

A. Whole Mount Preparation

Killing and fixing

In case of live specimens they are to be killed. Killing must be instantaneous. This is done with chloform, ether, acetone, alcohol, formalin, menthol, Bouin’s fluid etc. These chemicals serve as fixatives also. Specimens contracting or retracting suddenly in contact with chemicals are narcotised with menthol, thymol, poisonous gas etc. and then killed.

Staining

Staining is the act of giving colour to something. The killed or preserved specimens are thoroughly washed with water. This is followed by staining. In case of aqueous dyes, the specimens are first stained and then dehydrated. Dehydration means removal of water. In the use of alcoholic dyes the staining is done after dehydration to that concentration in which the dye is dissolved.

The period required to stain a specimen depends both on the size of the object and concentration of the dye in the solution.

Over staining, if any, is corrected by treatment with extremely diluted acid solution in water or alcohol according to the case, for a short period followed by immediate washing with water or alcohol. The water is removed from the specimen in steps by passing it through 50%, 70%, 90% and 100% alcohol.

Permanent Mounting

The dehydrated specimen is cleared in clove oil. The oil is washed in xylol and the specimen is mounted on a slide in canada balsam or DPX, and covered with a cover slip. Grooved slides are used for thick specimens.

Temporary Mounting

Specimens do not need dehydration or cleaning. Mount in water or saline solution or in 50% glycerine. If required the cover slip is sealed with bees wax or nail polish. A turn table is very convenient for the purpose.

B. Histological Preparation

Collection of tissue

For sectioning, tissues are to be collected from live specimens. In small vertebrates, the animal is paralysed by damaging the brain. In larger vertebrates, the same result is achieved by striking the head against a hard object. In still large species the tissues are collected immediately after killing the animal for some other purpose or a small piece of tissue for some other purpose or a small piece of tissue is cut by surgical operation. In invertebrates, the tissues are usually collected from live specimens without such pretreatment.

Fixing

Killing the tissue without any structural or chemical change is known as fixing.

In practice, it has not yet been possible to prepare a fixative which satisfies all the requirements fully.

The tissues are cut into small pieces, washed with physiological solution, if required, immersed in the fixative and left there for a definite period. The common fixatives used are Bouin’s fluid, Zenker’s fluid, Carnoy, Carnoy-Labrum etc. The specimen tubes with the fixative and tissues should be subjected to a vacuum pump for a few minutes to remove any air in the tissue which may enter during collection. Air interferes with the processing. The time required for fixation varies with the tissue.

Washing

This is usually done with water till the reagent is completely removed. If the per cent of water in the fixative is below 50, it should be washed only in solution recommended for the purpose.

Dehydration

Carry the tissues through grades of alcohol, viz. 50%, 70%, 90% and 100%, the period of treatment with each grade depending on the size of the tissue. Give two changes in absolute alcohol.

Claring

Transfer the tissue to ceder wood oil. Within a few days the tissues turn transparent and are ready for infiltration.

Infiltration

This is to replace oil with paraffin. The intercellular spaces are completely occupied by paraffin.

The tissue is washed in xylol and transferred to a covered porcelain crucible containing xylol and molten paraffin at a ratio 1:1 and the crucible is put in a temperature controlled paraffin bath for 10 to 15 minutes. After the period, the tissue is transferred to another covered crucible containing molten paraffin only, kept in the same bath. The time required for infiltration varies with tissues. Usually infiltration is completed within 90-120 minutes. After the desired period paraffin blocks are made with the tissues.

Paraffins of different melting points are used in different seasons.

Section cutting

This is done with a microtome. Sections for routine work are cut 5-6 micrometer thick. A grease free slide is taken. One side of the slide is marked with the help of a diamond pencil. A droplet of Mayer’s albumen is smeared on the marked surface. A thin film of water is put on the slide and the paraffin ribbon with sections are put on it. The slide is heated on a hot plate and the sections are properly stretched. The water is drained off and and the slide is dried on a hot plate.

1. Complex esters of monovalent alcohol and Fatty acids- 70.4 %-74.7%

2. Free acids- 13.5%-15.0%

3. Saturated Hydrocarbons 12.5%-15.5%

4. Some pigments and scented materials.

Propolish is the Resin produced by the honey bees from pollen grains of flowers.

Royal Jelly:

The acidic nitrogenous secretion of the Hypopharyngeal glands of worker-bees, which is fed exclusively to the queen.

Bee-Bread:

The soft gelatinous food of the workers produced by the workers from Necter, honey and the secretion of the “brood food” gland.

Pollen basket:

The collected pollen is stored in spacious area present at the junction of Basitarsus on both sides of the tibia of metathoracic legs, which is known as pollen basket.

Bee-Wax:

Bee-wax is, in fact, the secretory product of the abdominal gland of honey bee. After secretion , the product is brought to mandibles by the legs, which after proper grinding gives rise to Bee-wax.

What is Honey?

Honey is sweet, sticky, faint yellow colored liquid found inside the honey chambers of beehives, made of 78% carbohydrates, 17% water and some enzymes.

How is it formed?

Worker bees collect necters from the flowers and store temporarily inside their crop. The necter becomes modified there with the action of enzymes into Dextrose and Livulose rich honey.

Components of Honey

Livulose, Dextrose, Sucrose, Dextrine, minerals (Ca, P, Fe, K, S, Mn), different organic acids, enzymes, pigments, tissue parts of bees, water etc.

Salient Features:

1. Exclusively marine and cosmopolitan, found in all seas and at all depths.
2. Mostly sedentary (fixed), some palagic or free swiming.
3. Simple (solitary), aggregated in groups or composite (colonial).
4. Size (0.25 to 250 mm), shape and colour variable.
5. Adult body degenerate, sac-like, unsegmented, without paired appendages and usually without tail.
6. Body covered by a protective tunic or test composed largely of tunicine similar to cellulose, hence the name Tunicata.
7. A terminal branchial aperture and a dorsal atrial aperture usually present.
8. Coelom absent. Instead, an ectoderm-lined atrial cavity present which opens to outside through atrial apertures.
9. Notochord present only in larval tail, hence the name Urochordata.

Phoresy: A relationship between host and commensal involving only passive attachment of the commensal to the surface of the host (e.g., barnacle on whale). The supporting partner must be continuously moving.

Parasitoid: An organism that is parasitic only during its larval stage.

An animal that lives in or on another animal (the host), which it consumes and eventually kills. Hence, parasitoid may be regarded as intermediate between a true parasite and a predator.

Many wasps and other hymenopterans and also some flies, are parasitoids for part of their life cycle, laying their eggs commonly in or on the larvae of other insects. The hatched parasitoids then use the tissue of their host for food during development into free-living adults. At maturation they emerge and usually do cause death of their host (unlike most of the parasites).

Parasite:

An organism that depends on its host for some essential metabolites and must do some harm to its host, whatever small it may be.

Hyperparasitism: A situation in which a parasite occurs on or in another parasite , e.g., Rat intestine’s parasite Giardia muri is parasitized by Entamoeba pantista.

Predator: Living by preying upon other animals. The predator consumes all or part of its prey, generally killing the latter.

Parasitism is generally a heterospecific association in which one species (Parasite) depends on the other (host) for food and shelter and does harm to the other. Intraspecific parsitism is found in Schistosoma.