3.2.1. Environmental factors concerned with breeding of fishes

Unit 3 - Breeding of major carps

3.2.1. Environmental factors concerned with breeding of fishes

Environmental factors concerned with fish breeding are
  • Light
  • Temperature
  • Ecological factors
  • Meteorological conditions

These factors are known to play important roles in stimulating the release of pituitary gonadotropins, thereby controlling reproduction in fish.

Light

  • It is an important factor that controls reproduction in fish.
  • Early maturation and spawning of fish as a result of enhanced photoperiodic regimes.
  • In India, Cirrhinus reba was found to attain early maturity when subjected to artificial day lengths longer than natural day even at a low temperature of the winter months, viz. 19-20oC.
  • The resorption of gonads in C. reba was delayed and spawning conditions could be maintained up to November.

Temperature

  • The role of environmental temperature on sexual maturation and spawning of fish in India has been studied.
  • All observations show that there are optimum temperature ranges for induced breeding of cultivable fishes and critical temperature limits, above and below which fish will not reproduce.
  • The Indian Major Carps are found to breed within a range of 24-31oC.
    Beyond this range fish do not spawn.
  • The Chinese silver and grass carp have been successfully induced bred at temperatures 28.2oC to 34oC.
  • It was observed natural spawning of pituitary injected grass carp at a water temperature varying between 28.9 and 31.1oC, the optimum being 27oC, as in the case of Indian Major Carps.

Other Factors

  • It was opined that fresh rainwater and flooded condition in a tank are the primary factors in triggering the spawning of carps.
  • The presence of repressive factors may be responsible for inhibiting spawning of carps in confined waters, but when this repressive factor is sufficiently diluted by the onrush of floods in bundhs or ponds, spawning occurs.
  • Some workers suggested that it is the sudden drop in the electrolytes level in the environment caused by heavy monsoon rain or water current which induces gonadal hydration, resulting in natural spawning of carps.
  • Rain water and weather condition are important factors for induced breeding of fish.
  • Successful spawning in the majority of fishes has been induced on cloudy and rainy days, especially after heavy showers.
  • The carps are known to breed at a fairly wide range of pH and dissolved oxygen content.
Last modified: Thursday, 9 June 2011, 8:56 AM