Methods of fish seed collection

METHODS OF FISH SEED COLLECTION


Collecting eggs or fry from the wild was the first method used in obtaining stocking material. This is still followed for species for which the spawning behaviour is not controlled or not well understood, or for which the costs of artificial propagation are too high or where fry in large quantities is easily obtainable. Means of collection differ with species and the source.

Many of the cultivable fishes breed in the natural habitats like rivers, estuaries and sea. Hence collection of their seeds (young fishes) from the natural environment can be undertaken. The collection methods would vary according to the source.

Catfish

  • It is difficult to reproduce this fish in captivity. Hence, eggs are collected from the wild by placing bamboo traps in areas where this fish spawns. The traps are placed on rocky bottom and in deep water (4 – 6 m) by fishermen and the catfish spawns inside the bamboo tube. This method has allowed the collection of up to 2 million eggs even outside of the peak spawning periods. The eggs are transported to the hatchery, and placed in artisanal jars made from empty plastic bottles. Two or three days after hatching, the larvae are transferred into tanks made of plywood and covered with polyester resin measuring 2.4 × 0.4 × 0.3 m at a density of 5,000 - 10,000 per tank.

Milk fish

  • The milk fish (Chanos chanos) is one of the most important brackish water species that is widely cultured. The fish reproduces once or twice in a year in coastal waters of 25 m in depth. The eggs hatch in about 24 hours. The larvae drift to the coastal waters near the estuaries with a temperature of about 23°C. The fish seeds can be captured where phytoplankton is abundant using scoop nets or simple seine nets. The best time for collection is at the spring tide, and the three days before and following the full moon. Sandy beaches, a slight slope, and clear, calm water are ideal.

Mullet

  • Mullet is cultivated around the world, and have a large distribution. Mullets belong to the genera of Mugil or Liza sp. Although artificial reproduction is possible, there are still many instances where fry available in large quantities is collected from the wild. The mullets reproduce in the sea, and will thrive well in the sea, in estuaries,  and sometimes migrate to freshwater. The eggs are pelagic, and hatch in the following two days. After hatching, the larvae begin to swim near the coast where they usually arrive in mass after 2 months. At this point, they have reached a size of 25 mm. On the coast, they form small schools and begin to move towards the estuaries. The capture is usually done as they enter the estuary, at low or rising tide, using seine nets, dip nets, etc.

Shrimp

  • The various stages of post-egg development occur in the sea. After roughly 3 weeks, the young, termed post-larvae, begin to migrate to estuaries. The larvae are attracted by light, and are often collected by seine nets at night. Larvae can also be collected by using bunches of palm or coconut branches lashed together and placed on the bottom of the lagoon. After a few days, the traps are surrounded by a fine mesh net and the branches removed.
Problems with natural seed collection compared to reproduction in captivity
  • In certain cases, it is not possible to reproduce fish species in captivity. However, but the capture of fry from the wild presents some problems. Sometimes the sorting out of species at the fry or fingerling stage is difficult, which will result in a mixed stocking population of different species - some fast growing, some slow growing, some predators and some competitors also - into the pond.
  • Identification keys for fry and fingerlings are not often available.
  • Diseases and parasites affecting wild fish can be introduced into the pond.
  • On the other hand, fry collected in nature have usually already passed the most critical stages of their life cycle where the mortality is high and have good survival rates when stocked.
  • When a desired species of fry is being collected, the fry of other species also gets collected which may lead to the depletion of a group of fish stock.   
Last modified: Thursday, 31 May 2012, 10:34 AM