Fish of sea (2)
(Claude Achille)

“Aren't the watery directions in parallel with the terrestrial directions in their association with the element which they occupy? ”

Conditions of habitat

Each fish species has a medium of life in which it is liked.

This medium of life depends on:
-      The temperature: Many fish species cannot support of violent one change of temperature and live in a constant temperature.
-      Salinity: The majority of sea water fish die in fresh water, the salinity of a sector often gives the type of sought species.
-     The light: Some species dive the night and go up the day, others like the light, if important for the development of the seedlings and planktons.
-      Food: The areas or the plankton is abundant (currently identified by a cartography) are full of fish.

The temperature and the light in sea water are thus for the objective fishes.

The temperature

When the medium is thermically homogeneous the temperature varies regularly with the depth: isoclinal profile.

One observes sometimes a brutal thermal stand-off for a very weak variation of depth, this stand-off is called , present in all the seas and oceans with approximately from 15 to eters, it has a very large importance for certain pelagic fish species and their preys. Areas, for the tested professional fishermen, of very great interests.

In Polar water: A layer of water lower than 0° C located between surface and the content will be for the species placed in lower part an insuperable barrier. This thermal barrier is called “veil” without life in its bosom.

The knowledge of the temperature is thus for the search and the detection for certain species.

Example:

·        The cod life enters       = 0° and 10°
·        The herring life enters      = 5° and 12°
·        The mackerel life enters      = 6° and 20°
·        The sardine life enters      = 10° and 21°
·        The albacore life enters      = 15° and 20°

The temperature has a great influence on the development of fish, their migration and their appetite.

The study of the marine currents can help in search of well defined species. The large worldwide, hot or cold currents, convey the life in their bosom. A considerable progress was made with the appearance of the bathy-probes recorders, they give simultaneously salinity and the temperature plus the depth. They calculate an approximation of the relative density, parameter of oceanic dynamics: principle of .

Each sea fisherman could deny only his own seasonal identifications on a defined species, cannot escape the great movement from the hot or cold currents, according to the seasons of fisheries. Thus the old ones prepared their fishing tackle by looking at the migration of the birds.

The direct relationship between the temperature, salinity and the luminosity acting on the marine ecosystem the fisherman is thus influenced, like its preys, by the natural balance of the life of the seas and oceans of our planet.

Photosynthesis exploiting a part the planktonique production, using the temperature, the light, rock salt and carbonic gas, we can make the following remark: The nitrates and phosphates being employed like manure, they provide nitrogen, which is one of the main elements which the animals and the plants need to be nourished; the first elements of the food chain are directly victims or recipients of the new terrestrial ecological data.

Personally I noted that the algae in their great majority are much more numerous on the coasts than I attend since my more tender youth. Sectors or I fished with foot are now covered with algae of the laminar type. It is obvious that the influence of the terrestrial rejections of it is responsible, but which can say “I will not use more my washing machine the linen, nor of manure in my garden! ” Only the true problem remains the abusive use of weeding which is a catastrophe on the ecosystem of water.

The temperature of water operates the mechanism of the migration

-      Migration of concentration: it takes place at the time of the reproduction and occurs in the southernmost party of the sector attended by the species, because the fish need, to lay, of an higher temperature to that which they usually support.
-      Migration of dispersion: the purpose of it follows the laying and is search of food in water of temperature being appropriate for the species.
-     Vertical migration: certain fish (sardine, mackerel, herring…) vertical migrations day laborers under the influence achieve, thinks you one, of the temperature and solar light. In general, they remain during on the underground and rise the night while following, at least for sardine and herring, the migrations of the plankton which constitutes their food.
-      Migration : fish migrate of the rivers towards the sea. The salmon is born in river, migrates at sea then returns to reproduce in river.

-      Migration : Fish migrate of the sea towards the river. The eel is born at sea, migrates in river then at sea turns over to reproduce.

Reproduction of fish

Sexes

The fish can be:

-          or . They are either male, or females (the mackerel…)
-         HERMAPHRODITES, i.e., whom they have at the same time of the male and female .
-         , fish hermaphrodites which pass, during their life, of the stage female to that of male (the sea-bream…)
-         , fish hermaphrodites which pass, during their life, of the stage female to that of male (the …)

Conditions of reproduction

To be able to reproduce, the fish must be mature, i.e. to have the age to reproduce: one speaks about sexual maturity.

-         The genital glands are called . In the females ovaries, of orange red color and lengthened form; in the male, sperm is of color white and called milt.
-         In many osseous fish, the male forwards a bridal ornament; it then takes bright colors and brilliant.
-         The laying generally takes place when water is at a certain temperature (cold in the Arctic fish, heat at the tropical species)
-         Many fish change latitude at the period of reproduction because they reproduce at a well defined temperature.
-         The place of the laying is called Frayère, the result of the laying is called Frai.

Type of reproduction

 The various stages of reproduction are the following ones:

-         Oviparous animals
-        The ovoviviparous ones
-         The viviparous ones

The fish oviparous animals: The majority of the fish are oviparous animals. The female lays the ovules    (before fecundation) the male spreads its milt on the ovules in full water or close to the content. The fertilized ovule gives an egg. The eggs are, either pelagic (floating between two water) or benthic (falling on the content) the egg hatches before the baby finished developing to give rise to a larva.

Gestation is stopped, this larva cannot only be nourished; it thus nourishes its vitelline crucible, until it becomes alevin.

At the time of the reproduction, much of ovules are not fertilized, This is why the fish oviparous animals lay many ovules.

There can be reconciliation of the males and the females in groups very few or, as at cod or haddock, formation of couples. Both swim then coupled one with the other, belly against belly, so that their genital openings are touched.
 

Ovoviviparous fish: The are ovoviviparous like some osseous fish (rosefishes, scorpion fishes…)

There is coupling when the male part ( among ) enters in the genital opening of the female. The ovule is fertilized in the body of the female.

The egg hatches after incubation, when the baby finished developing, to give rise to a alevin.

Viviparous fish: Certain are viviparous. Example: the blue shark, the line …

Fecundation is internal: there is coupling

The laying takes place at the same time as the blossoming. There is birth of a alevin similar to the adult.