Stress free grading of finfish fry and fingerlings.

October 2003

H.C.M. van Herwaarden

For most finfish a uniform size distribution of the fingerlings at stocking is of great importance for optimal growth performance of the population and size distribution at harvest. A uniform size distribution of fries and fingerlings is usually achieved by grading the fingerlings manually with graders. This process, which usually involves overcrowding in water that rapidly becomes oxygen deficient, causes excessive handling-stress and damages to the fish. Especially when large numbers of fish have to be graded the integrity of the fish is compromised by these stress inducing factors.

AquaCrops has developed the “passive grading-purging system for finfish” which enables commercial hatchery operations to grade and purge fingerlings with minimal handling stress. A pilot model of this system was successfully tested on a tilapia hatchery in the Philippines. The passive grading-purging system forms a reliable and cost effective alternative to expensive commercial packages.

Summarised the passive grading-purging system has the following advantages.

Advantages:
·    Grades fish with high level of accuracy.
·    Reduces handling stress during grading and purging.
·    Increases survival of fish during grading.
·    Reduces damages to fish during grading.
·    Separates healthy from moribund, weak or diseased fish.
·    Easy to operate.
·    Reduces manpower input.
·    Can be constructed anywhere in the world with local available materials.
·    High flexibility in dimension and capacity.
·    Construction plan and operating manual available through the internet.

Disadvantages:
·    The system requires the complete system set up, i.e. grading principles cannot be incorporated in
     existing systems.
·    Grading requires more time compared to conventional systems.

Use of the passive grading-purging system will result in reduced post-stocking mortality and lower susceptibility to diseases, which in turn will positively effect growth performance and profitability.The system is designed for large scale hatcheries of fin fish. The capacity of the system depends on its size which can be adapted to local conditions. Full blown systems can grade and purge up to 500.000 fingerlings per day.

A detailed "construction plan and operation manual" of the passive grading-purging system is now available. Please contact AquaCrops for more information about the system, pricing and how to obtain a copy, or retrieve the "construction plan and operation manual" by pressing the button below if you already have received your password.