Growth of Fishes (With Diagram)

In this article we will discuss about the growth of fish.

Growth is a characteristic feature of living beings. Every organism grows and attains its normal size. Growth is actually an increase in any dimension of any organism in relation to time. Growth is the process of addition of flesh as a result of protein synthesis.

Knowledge of fish growth is of vital importance for obtaining high yield of fish. The rate of growth varies from species to species and sometimes it varies even among species also.

Rate of fish growth is influence by many factors:


1. Different Localities:

Individuals of same species grow at different rate in different localities.

2. Seasonal Effects:

The different temperatures in different seasons affect growth of fish. In summer the fish grow fast, however, in winter growth is slow.


3. Availability of Food and Oxygen:

This is the most important factor influencing growth of fish. In ecologically balanced water body, growth rate is high because of ample supply of oxygen and food.

4. Population Density:

Higher population density shows slow growth while low density shows high growth rate.


5. Age:

Fish continue to grow throughout their life but with increasing age, growth rate is slow and in extreme old age fish growth is extreme slow. Growth slows down at the onset of sexual maturity when large amount of nutrient material periodically go into egg or sperm formation.

6. Adaptive Character:

Sharks and Sturgeon grow very fast into large size because of constant food supply, which provides protection against their predators. However, in Goby growth is slow, resulting in small size of the body. This is an adaptation to overcome problem of limited food supply and is related to increased reproductive capacities as they have more danger of destruction by predators.


Growth Curve:

Growth curve is obtained when either length or weight of a fish is plotted against time periods. The curve obtained is sigmoid or S-shaped. This curve illustrates the rate of growth. If rate of growth is plotted against time, such curve is known as growth rate curve (Fig. 14.3a, b).

Growth Curve and Growth Rate Curve

Linear Growth:

Fish growth varies according to various periods. Maximum growth rate is found just before attaining the sexual maturity of fish. After maturation of gonads the growth slows and decreases. A linear growth pattern is seen during the postnatal development of fish, specially during the period of hatching to the sexual maturity.

This may differ from species to species, and depends on various factors, viz., appropriate and balanced food, optimum temperature for vital activities like metabolism, vitamins and trace elements for proper growth. Fluctuation in these factors affects growth rate of the fish. If there is scarcity of food the size of fish will be small, and, if the availability of food is restored to normalcy, the fish grows to normal.

Determination of Length (Linear Growth):

The scales of many fishes have permanent marks, which is considered as confirmation of both age and growth. This evidence provides the base of estimating yearly changes in growth and also of calculating the length of body. Annuli formed during winter shows zone of retarded growth.

There exists a relationship between the annuli and the growth of the fish. Thus body length can be estimated by studying the relationship between the scale size and the body size.

Back Calculation of Length

Some important methods are as follows:

1. Direct Proportion — Body/Scale Relationship Method:

This method is based on the facts of isogonic growth rate, which shows that the growth of the scale and the body occurs at the same proportional rate. However, the calculated body length is found to be less than its empirical length. This is because of the fact that fish attains some length before scale formation.

Following formula is applied to calculate the length of a fish:

This method is useful in calculating the length of fish at early stages. The above formula works well when fish shows a linear and directly proportional body. For example if a fish has L = 600 mm, S=10 mm, S+ = 4 mm, then the length of the fish at the time of formation of first annulus can be calculated as follows:

Here the fish shows a non-linear but not directly proportional growth of body and scale.

2. Dahl-Lea Method:

This method states that there is a curvilinear (sigmoid curve) relationship between body length and scale length and not a straight line (linear) relationship.

Therefore, a correction factor is used and the past length is calculated as:

L = C S, where L = body length, S = scale length and C = a constant,

or, log L = log C + n log S, where C and n = constants from data.

It is observed that body/scale relationship varies from species to species.

Length-Weight Relationship:

Weight can be calculated by a formula:

W = KL3, where W = weight, L = length, K = constant; for fish showing symmetrical or isometric growth throughout.

The body form and specific gravity of a fish change constantly with the advancement of age. Thus simple cube W expression therefore does not seem to be correct throughout the life history of fish, as the value of K is not constant but subject of great variation.

A more satisfactory formula is:

W = Ln, in which W = weight, L = length, n = constants for log W = log C + n log L.

Linear Growth and Condition of Fish: Coefficient of Condition Factor:

The ratio of length and growth represents the condition at any given time. When this ratio is calculated and if the obtained value is large, it indicates better condition of fish. The Fulton’s formula is used to express condition of the fish.

Q = W100, where Q is coefficient of condition

I3 W is the weight of fish and I is the length

Coefficient factor or coefficient condition is that state in which a fish remains for a certain period.

This value is useful in elucidating the following:

1. Difference in conditions of the individuals of same species in different water.

2. Differences among individuals of same length.

3. Differences occur due to seasonal changes in relation to the age and sex of the fish.

There is another way to know the condition of the fish by estimating the fat contents, which is related to linear growth of fish. During the period of winters, migration and spawning, the major fat contents are saturated fatty acids. This type of fat is used for long- term use. On the other hand, unsaturated fatty acids are present in fat when the fat is deposited for use in daily maintenance.

Food Consumption and Growth of Fish:

Food plays an important role in the growth of fish.

Food consumption rate is estimated by the following methods:

1. Samples of fish are collected from the nature. Then quantity of food present in the stomach is determined followed by estimation of rate of gastric digestion.

2. By determining the intake of nitrogen, which helps in the growth, and the loss of nitrogen in excretion through kidney and gills.

3. By comparison of food consumption and growth rate between the fish from natural habitat and the fish kept in captivity. It has been found that the total amount of food consumed is not used for growth. Only a small amount of food is utilized for growth.

Hence it is necessary to know about the fate of consumed food, which is as follows:

(i) Some part of food is neither digested nor absorbed and is passed out along with faeces.

(ii) A part of ingested food is digested and absorbed by the gut.

(iii) Some part of absorbed food is excreted through the kidney, gall bladder and skin.

(iv) Some part of assimilated food is used for maintenance of metabolism.

(v) Some part of assimilated food is used for growth.

Life Span of Fishes:

It has been observed that generally species with large individuals seems to exhibit older age than species consists of small fish. Many fishes that attain size of 12 inches show a life span of at least 4 to 5 years. However, age of fishes in captivity, i.e., in the aquarium may be expected to be more but do not exceed to 5 years.

Factors Affecting Fish Growth:

1. Abiotic Factors:

Fishes show a considerable variation in their growth rate and age of sexual maturity in northern and southern waters. Temperature plays an important role as it affects metabolism and food consumption in fishes. The seasonal increase in the temperature of freshwater bodies cause increase in natural food for fishes.

Fishes grow at faster rate at the optimum temperature, at which their appetite is high and requirement of maintenance is low. The optimum temperature varies from 7°C to 19°C in case of brown trout (Solmo trutta).

Light also affects the rate and pattern of fish growth. Intensity of light depends on the length of the day. Light causes increased thyroid activity resulting the increased swimming activity and reduction in growth rate in experiments with the brown trout (Salmo trutta) in mid-summer. Longer days are advantageous where feeding is accomplished by sight whereas shorter days are beneficial when the food is abundant.

2. Biotic Factors:

The population density is also of a vital importance. Among the fish population there is competition for food, nest site and so occur, which may affect the growth of fish. High density of fish in a place can also affect the fish growth. It has been described that the fish in a crowded condition may release a chemical substance known as “crowding substance”, which prevents growth.

3. Genetic Factor:

Growth and size of the fish are genetically determined. Size difference between the sexes may be due to genetic factors.

4. Endocrine Factor:

Several metabolic hormones like insulin, thyroxin, gonadal and adrenal steroids produce synergy which affects the growth. In carefully controlled experiments, Higgs, (1977) treated groups of yearling coho salmon with bovine growth hormone thyroxin and methyltestosteron, given separately and with the combination of these three substances maximum growth was obtained.

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