Stomach content analysis and age determination

PROCEDURES FOR STOMACH CONTENT ANALYSIS

The state of the stomach can be determined visually before dissection and categorized as follows:
0/4 OR 0%   -  Empty stomach
¼ or 25%   - One quarter full stomach
½ or 50%   - Half full stomach
¾ or 75%  - Three quarter full stomach
1 or 100%  - full stomach

STEPS
-Identify the specie to be analysed
-Take the standard length, total length and weight of the fish.
-Determine your sample size i.e. the number of fish to be use.
-Collect your sample fish.
-Transport them to the laboratory using the preservative agent like Ice or formalin to prevent autolysis
-Dissect your fishes using the dissecting set.
-Carefully remove the alimentary canal and cut out the stomach.
-Using a guide book carefully classify material found in the stomach.
-State the frequency of occurrence to determine the feeding habit.

PROCEDURES TO DETERMINE AGE AND GROWTH OF FISH USING SCALE

There are different stages to be taken in other to determine the age of fish using the hard part and these are as follows:

-Identify the fish to be used
-Procure a random sample of fish large enough to include representatives of all sizes and ages.
-Record for each specimen, the date, place and manner of collection
-Determine the sex, measure the standard and total lengths and weight of each individual fish.
-Take from each specimen the structure that will be used for age determination.
Scale – Collect below and above lateral line a particular position on the fish;
-Process this structure (scale) by cleaning then boiling for about 30minutes
-Observe under the microscope using an eye piece
-Count the number of annuli ring found under microscope and record it.
-Scale with one annuli ring is one year old, two rings denotes 2 years old.
-Assign an age to each individual and relate it with the length and/or weight of fish. For fish that is less than 1 year- 0+ is assigned, more than 1 year but less than 2 years – 1+, 2+, 3+ etc.