Divalent cations are generally eliminated in marine fishes through

Options

A. Gill membrane
B. Anal membrane
C. Fecal matter
D. Oral membrane

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks how marine fishes eliminate divalent cations. Divalent cations include ions like calcium (Ca²⁺) and magnesium (Mg²⁺), which have a +2 charge.

2. **Identifying Excretion Mechanisms in Marine Fishes**: Marine fishes have several mechanisms for excreting waste products, including:
- Gill membranes
- Anal membranes
- Oral membranes
- Fecal matter

3. **Analyzing the Role of Gill Membranes**: The gill membranes contain specialized cells known as ionocytes or chloride cells. These cells primarily help in the excretion of monovalent cations (like Na⁺ and K⁺) and not divalent cations. Therefore, gill membranes are not responsible for the elimination of divalent cations.

4. **Considering Anal and Oral Membranes**: The anal and oral membranes are involved in the excretion of water and dissolved salts but do not specifically target divalent cations. Thus, they can also be excluded from the options.

5. **Identifying the Correct Mechanism**: The elimination of divalent cations occurs primarily through fecal matter. Marine fishes excrete these ions in their feces, which allows them to regulate their internal ion balance effectively.

6. **Final Answer**: Therefore, divalent cations are generally eliminated in marine fishes through fecal matter.