Question

Number of larval stages in the freshwater prawn M. rosenbergii is

• A. 11
• B. 3
• C. 6
• D. 9

Hint:

Macrobrachium rosenbergii Biology: Exactly 11 ZOEAL LARVAL STAGES. Requires $12 - 15\text{ ppt}$ brackishwater for larval rearing. Metamorphoses into benthic Post-Larvae (PL).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Larval ontogeny and metamorphosis in the giant freshwater prawn (Macrobrachium rosenbergii): passing through 11 distinct planktonic zoeal larval stages before metamorphosing into benthic post-larvae (PL).
Key Formula or Approach:
\[ \text{Egg} \xrightarrow{\text{Hatching}} \text{Zoea I} \rightarrow \text{Zoea II} \rightarrow \dots \rightarrow \text{Zoea XI (11 Larval Stages)} \xrightarrow{\text{Metamorphosis (Day 22--35)}} \text{Post-Larva (PL)} \]

Step 2: Detailed Explanation:
Larval development of Giant Freshwater Prawn (Scampi Macrobrachium rosenbergii):
- Following hatching in brackishwater ($12\% - 15\%\text{ salinity}$), the larvae pass through 11 distinct morphologically defined planktonic Zoeal Larval Stages (Zoea I to Zoea XI) over a developmental period of 22 to 35 days:
1. Stage I (newly hatched, sessile eyes, $1.9\text{ mm}$).
2. Stage II (stalked eyes).
3. Stages III--XI (progressive development of uropods, telson, chelipeds, and pleopods).
- At Stage XI, the zoea undergoes complete terminal metamorphosis into the benthic, crawling Post-Larva (PL), which migrates back into freshwater.

Step 3: Final Answer:
Hence, the number of larval stages in M. rosenbergii is 11, corresponding to option (A).