parental behaviour in animals (especially in fishes)

PARENTAL CARE:A BRIEF

Looking after the eggs or the young until they are independent to defend themselves from predators is known as parental care. In other words, parental care is any action or behavior performed by the parents towards its offspring that increases its chances of survival. Parental care behavior is any behavior performed after breeding, by one or both parents, that contributes to the survival of their offspring and animal exhibit a great diversity in care of their eggs and young during development.

Parental care in fishes

       

   Parental care  behavior is universal among fishes.

         Fish show all grades of parental care behavior from random spawning and from deposition of large number of uncared eggs to the protection of young. The lack of parental care behavior is correlated with the production of great number of eggs and sperms..

·         Two general types of variation in parental care behavior exist among fishes. First either both parents, or one alone cares for the offspring. Thus, there are paternal, maternal and biparental species. Second, the eggs and newly hatched young are either maintained on: substrate - that is, on plants, under stones, in excavated pits and so on (these are called  substrate-brooders or guarders) or carried about in the parent’s mouth (these are called mouth brooders or incubators). Fishes have evolved many means of affording care to fertilized eggs and young ones by one or both sexes.

·        Scattering eggs over aquatic plants. In some fishes such as pikes, Esox lucius;carps, Cyprinus carpio, Carrassius auratus,etc., eggs are scatteredusually over aquatic plants to which they are attached.

·        Depositing eggs in sticky covering. In many carps, eggs are usually laid with some special sticky covering by means of which they are attached to each other and to the stones, weeds, etc. In yellow perch, Perca flavescens eggs are deposited in a rope of single mass.

·        Layings of eggs at suitable places. Suitable spawning grounds are selected by anadromous fishes such as Salmo solar, Acipenser, Oncorhyncus, etc. They dig excavation in gravel substrate, lay their eggs in the pits, cover them with gravel and desert them. The sand gobi Pomatoschistos minutus lays its eggs in some protected spot where they are guarded by the male who aerates them by his movements.         

   The male African lung-fish, Protopterus, prepare a simple nest in the form of deep hole in swampy laces along the river banks. After spawning he guards the nest. The South African lung fish Lepidosiren also prepares a nest in the form of a burrow and the male develops highly vascularized filaments on its pelvic fins for aeration. The male bowfin, Amia calva, of the great lakes of North America builds a crude circular nest among aquatic vegetation. The male stands on guard till the young ones are hatched. The young ones leave the nest only under the protection of the father.
   
   Before the onset of its courtship, the male stickleback, Gasterosteus aculeatus and ten-spined stickleback, Pygosteus pungitius) build a quite elaborate spherical or elongate nest. The nest is built by collecting plant fragments, rootlets and then binding them together with adhesive kidney secretions. The various activities of male such as probing, boring, sucking and glueing, result in the formation of a compact nest with an internal chamber (tunnel) to receive the eggs. Male drives and induces the female into the nest for laying eggs, then chases her away, enters the nest, fertilizes the eggs and guard them from intruders.

           

             The most elaborate nest is made by Apelts quadracus; its cup-shaped nest is attached to rooted plants close to the bottom. After a clutch of eggs is laid, the male builds an extension of the nest up and over the eggs, with a concave upper surface to the extension. A second clutch of eggs is laid on the new nest floor and this procedure may be repeated several times, until the male has several clutches of eggs stacked vertically within a single multi-tiered nest.

            Floating nests are made by American catfishes, in which the eggs are suspended in a mass of bubbles and mucus produced by the fish. The male Siamese fighting fish (Betta splendens) too builds floating nest and sticks the fertilized eggs to the lower surface of foamy nest. He stays on guard on this nest and fights till death to defend it. The male paradise fish, Macropodus also prepares a similar foamy nest.

 ·         Coiling round the eggs. The butter fish (Pholis gunnellus) rolls all eggs into a ball and curls around it. 

·         Deposition of eggs by ovipositor in mussels. The female Rhodeus amarus (European bitterling) deposits eggs in the siphon of a fresh-water mussel (Swan mussel; by means of very long urogenital papilla (ovipositor). Male immediately sheds the sperms on the opening (of mussel) over the eggs.

 ·         Egg brooding in mouth and intestine. The female Tilapia mossambica broods the fertilized eggs in her mouth. She allows the young to take refuge in her buccal cavity in times of danger for some days after hatching.

 ·         Brood pouches. The male sea horse and pipe fish carry eggs in a brood pouch on the abdomen. In sea horse (Hippocampus) fertilized eggs are transferred by the female into the brood pouch on the belly of the male. These eggs are carried by males until their hatching. Eggs become embedded in the folds of the brood pouch and for the exchange of respiratory gases a sort of placenta is formed. 

            In the male pipe-fish (Syngnathus acus), a brood pouch is formed by two flaps of skin on the underside of the body on which eggs are placed by the female. The brood pouch develops an inner spongy lining which is ricnly supplies with blood vessels. The eggs get nourishment until hatching. Fry may return to the pouch when in danger.

 ·         Egg capsules. In oviparous Elasmobranches such as rays and cat sharks (Scyllium and Raja) fertilized eggs are laid inside protective horny egg capsules, called Mermaids purse. This capsule remains attached to the aquatic weeds by their tendrils. The development proceeds inside the capsule until the yolk has been used up. The youngs hatch out after rupturing off egg case. 

·         Viviparity (True internal incubation). Viviparity describes the highest degree of parental care and provide maximum protection to the young ones. In viviparous elasmobranches (e.g., Scoliodon, Mustelus) eggs develop in the uterus. The mucous lining of the uterus forms fluid-filled protective compartments, one for each embryo. Each embryo receives nourishment from the uterine tissues through the yolk-sac placenta.