Coastal Aquaculture and Mariculture (2+1)

Unit 6 - Culture of Crustaceans

6.1.2. Culture systems

• Mainly there are two types of culture systems – traditional and modern scientific. In traditional systems, natural stocking is achieved through intake of tidal water carrying large number of shrimp larvae along with unwanted predators and competitors. They are held in the pond over a period of time to grow and are then harvested. These culture systems more appropriately termed as ‘catch and hold’ culture systems evolved thousands of hundreds of years ago in the Mediterranean and are still commonly used today where labour and land costs are low. This approach can still be profitable with low risk although profits can also be low. The Pokkali field prawn filtration, Bheries of West Bengal, Gazanis of Karnataka and Khazans of Goa are the examples of this system of prawn/shrimp culture.
• While catch and hold approach requires minimal labour, capital and skill, it is also low yield and unpredictable. Neither stocking densities nor species composition are controllable. And improvement over catch and hold system is a grow-out system where pond source water is screened to control unwanted entrants, and the pond is then stocked with a known quantity of desirable species of shrimps. Shrimp seed are collected from wild are normally late post larvae or juveniles which are either stocked directly or nursed to a larger size before stocking. Although additional labour and skill are needed for this kind of approach, greater control is exercised over density, species, survival and growth and size at harvest. The grow-out locations can be far removed from the source of seed, greatly expanding potential farm sites.
• Although this system is commonly still used, it does have limitations. Seed availability is unpredictable since it fluctuates from season to season and year to year. Therefore there is potential for the farms to be under stocked or not stocked at all. This can lead to economic hardships. Additionally, it requires skill to distinguish seed of fast growing species from slow growing species. Ponds are often stocked with a mixture of species that are less optimal and results in reduced yields.
• The evolution of modern shrimp culture required captive reproduction and seed production through larviculture in hatcheries. The Japanese scientist Motasako Fujinaga (published under the name Hudinaga) laid the technical ground work for this development. He spawned wild spawners of P. japonicus in the laboratory, hatched eggs and reared the larvae to the size of post larvae suitable for stocking. Some species mature in captivity while others don’t. Eyes stalk ablation technique was subsequently developed to mature the spawners in captivity. This ensured year round availability of spawners and hence the seed could be produced anytime.

Modern shrimp farming

Modern shrimp farming can be divided into four types

1. Extensive
2. Modified extensive
3. Semi-intensive
4. Intensive.

• Extensive shrimp farming is characterized by large ponds, low stocking densities, with very little input and low levels of management and low yields per unit area. In places where labour is cheap and land is plenty, seed are abundant and inexpensive this form of shrimp culture is quite profitable. Neither use of expensive formulated feed nor high levels of pond management are necessary.
• Semi-intensive shrimp farming on the other hand requires high stocking densities in smaller ponds, high feed and high energy inputs, and continuous management attention and gives higher yields.
• Modified extensive shrimp farming falls between extensive and semi-intensive systems. Intensive system of shrimp farming is followed in advanced countries and is characterized by very high stocking densities and very high inputs of feed and energy with a concomitant high level of management attention aided by automatic systems. This kind of farming is not followed in developing countries where most of the shrimp farming occurs.