How to Identify good quality Post Larvae
Shrimp health management has become the main focus of improving production and minimizing infectious diseases in shrimp ponds for the smooth development of the aquaculture industry. To accomplish this goal, we should be concerned with the quality of post larvae especially the selection of high-health post larvae shrimp, before stocking in the pond.
Post Larvae selection is important as it will determine the performance and production of the ponds. The objective of larvae selection is to obtain the best survival and growth in the pond. There are several characteristics of good quality post larvae, and visual observation can be used in identifying good quality or healthy post-larvae for stocking.
Some of the useful criteria are given below to help farmers identify high-health post larvae:
1. Activity:
- Place some PL (about 100 pcs) in a basin, stir the water and check.
- Healthy PL will swim against the current. Weak PL will gather at the center.
2. Size:
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- Good and healthy shrimp Larvae should be even in size.
- PL 10 should have a total length of 10 mm.
- The 3 stages form one spine so PL 10 has 3 to 4 spines this is the main character of larval age finding.
- Uneven size may be due to different Stages, underfeeding, disease, poor water quality, or over-aged Post-Larvae.
3. Disease-free:
a) Check of larvae are red/pink in color - Caused by expansion of Chromophores,it indicates
b) Any chronic or acute mortality - Indicative of advanced disease stress
c) Any limb or appendage necrosis - Indicative of bacteria infection
d) Check of fouling organism, e.g Zoothamnium - Indicative of poor water quality Overfeeding
e) Check Hepatopancreas -
Brownish – normal
Whitish – disease problem
f) WSSV should be negative - Accepted with PCR
4. Gut:
-
- Full gut indicates good health, empty gut indicates possible stress problem
5. Molting:
-
- Molting problem, indicative of nutritional disorders related to sterol, phospholipids or calcium or phosphorous
6. Pigmentation:
(a) Shape
- Finger like – healthy
- Round Shape – unhealthy
(b) Color
- Rust like brown/gray / dark gray – healthy
- Yellow – average
- Blue – unhealthy
7. Muscle development:
The ratio of width of gut and body depth below the gut at the 6thsegment,
healthy PL should be 1:4 or > 4
8. Antibiotic usage:
-
- With: PL shorter, fatter and darker color sometimes with the crooked body.
- Without: PL longer, thinner and lighter color
9. Stress test:
-
- Use 200 PLs for the stress test
- Temperature – Lower temperature to 20oC in a short period (5-10 minutes)
- Strong healthy PL will survive no death should occur.
10. External features:
For a healthy PL, the antennal scales of head portion are closed together whereas the tail fan (uropod) is widely opened. Closed uropods are indicative of young fry not yet suitable for stocking (
11. Feeding activity:
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- Healthy PLs have a good appetite.
- After acclimatization.
- PLs should feed actively.
- When feed is available, the gut should fill up after 10-15 minutes.
