Salinity is one of the environmental factors that influence the growth performance of many fish. Salinity effects have been studied in several species of fish in ponds .

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Assignment of AAHM-223
Brijesh bairwa
Roll on. 17021017
(cof, dholi)
Role of salinity in fish
May 23, 2019
Introduction
Salinity refers to the dissolved salt content of a body of water. Marine
salinity levels are influenced by a number of factors including rainfall,
evaporation, inflow of river water, wind, and melting of glaciers.
Salinity can have a great impact on the type of organisms that live in a
body of water, additionally, salinity plays a critical role in the water cycle
and ocean circulation.
Salinity
Conceptually the salinity is the quantity
of dissolved salt content of the water.
Salts are compounds like sodium
chloride, magnesium sulfate, potassium
nitrate, and sodium bicarbonate which
dissolve into ions.
Seawater typically has a mass salinity of around ​35 g/kg​, although lower
values are typical near coasts where rivers enter the ocean.

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Rivers and lakes can have a wide range of salinities, from less than ​0.01
g/kg​ to a few g/kg, although there are many places where higher salinities
are found.
Salinity is an ecological factor of considerable importance, influencing
the types of organisms that live in a body of water.
Organisms (mostly bacteria) that can live in very salty conditions are
classified as extremophiles, or halophiles specifically. An organism that
can withstand a wide range of salinities is euryhaline. And short range of
salinity is stenohaline.
Objective
Why Is Salinity Important​? Salinity can affect the density of ocean
water—water that has higher salinity is denser and heavier and will sink
underneath less saline, warmer water.
This can affect the movement of ocean currents. It can also affect marine
life, which may need to regulate its intake of saltwater.
Organisms (mostly bacteria) that can live in very salty conditions are
classified as extremophiles, or halophiles specifically.
An organism that can withstand a wide range of salinities is euryhaline and
narrowed range of salinities is stenohaline.

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Development and growth (continuous in fish) are controlled by ‘internal
factors’ including CNS, endocrinological and neuroendocrinological
systems.
Among vertebrates, they also are highly dependent on environmental
conditions. Among other factors, many studies have reported an influence
of water salinity on fish development and growth.
In most species, egg fertilization and incubation, yolk sac resorption, early
embryogenesis, swimbladder inflation, larval growth are dependent on
salinity. In larger fish, salinity is also a key factor in controlling growth.
Do the changes in growth rate, that depend on salinity, result from an
action on : -
● standard metabolic rate
● food intake
● food conversion; and/or
● hormonal stimulation​.
Better growth at intermediate salinities (8–20 psu) is very often, but not
systematically, correlated to a lower standard metabolic rate.
Numerous studies have shown that 20 to >50% of the total fish energy
budget are dedicated to osmoregulation. However, recent ones indicate
that the osmotic cost is not as high (roughly 10%) as this.

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Data are also available in terms of food intake and stimulation of food
conversion, which are both dependent on the environmental salinity.
Temperature and salinity have complex interactions. Many hormones are
known to be active in both osmoregulation and growth regulation, e.g. in
the control of food intake.
All of these factors are reviewed. As often, multiple causality is likely to be
at work and the interactive effects of salinity on physiology and behaviour
must also be taken into account.
How can marine organisms survive in varying salinity​? In one
of the vitally important salt fingers (double diffusion convection in sea),
they support marine life but Most marine organisms have physiological
adaptations for dealing with fluctuations in salinity.
Some fish have salt glands that help regulate
osmotic balance, crustaceans have specialized
cells in their gills and antennal glands for
osmoregulation, and some some animals such
as echinoderms just conform to small changes
(3-5 ppt), but can otherwise be affected by
large changes in salinity.

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It takes energy to osmoregulate so metabolic demand increases during
periods of increased regulation.
That can impose stress to an animal. Some crabs, for example blue crabs,
osmoregulate at low (0-24 ppt ) and very high salinities (>40), and
osmoconformer at moderate salinities (24-37 ppt ).
Impact
Salinity has a huge effect on what species can exist in aquatic
environments. Salinity can be natural, such as sea water and estuaries
where incoming sea tides mix with outgoing freshwater's of river systems.
There are some species that can adapt their bodies accommodate these
salinity fluctuations.
Salmonids such as salmon and sea trout are good examples of this and
migration from sea to freshwater is an essential part of their life
cycle.Salinity changes in aquatic systems can also be attributed to
non-natural influences.

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Climate change and water flows alter the speed of desiccation which then
changes the water composition.
Reduced water, especially in rivers with dams or in areas of changing
climates can increase the concentration of the salts.