Shloka 40
मनु-उपदेशः — भूत-उत्पत्ति, इन्द्रिय-निवृत्ति, तथा पर-स्वभाव-विवेकः
Manu’s Instruction on Elemental Origination, Sense-Withdrawal, and Discrimination of the Supreme Nature
पृथग्भूतौ प्रकृत्या तौ सम्प्रयुक्तौ च सर्वदा । यथा मत्स्यो जलं॑ चैव सम्प्रयुक्तो तथैव तौ
pṛthagbhūtau prakṛtyā tau samprayuktau ca sarvadā | yathā matsyo jalaṃ caiva samprayukto tathaiva tau ||
ビーシュマは説く。両者は本性において別でありながら、常に結び合っている。魚と水は異なる存在でありつつ、生きられた現実において切り離せないように、アートマン（自己）と、 बुद्धि（ブッディ、知性）などの内なる器官もまた、本質は異なるが、身体をもつ経験の中で共に働くのである。
भीष्म उवाच
Educational Q&A
The verse teaches discernment: the self (ātman) and intellect/mind (buddhi) are inherently distinct, yet in embodied life they operate in constant conjunction. Recognizing this helps one act in dharma without mistaking mental functions for the true self.
In Śānti Parva, Bhīṣma is instructing Yudhiṣṭhira on philosophical and ethical foundations after the war. Here he uses the fish-and-water analogy to clarify how two different principles can remain inseparably associated in lived experience.