When executing a 'Salam' contract for a future catch, what precise attribute of the fish must be unequivocally specified at the time of contract formation to avoid 'Gharar'?

When executing a 'Salam' contract, which is a forward sale where the price is paid in full at the time of contract formation for goods to be delivered at a future specified date, it is a fundamental requirement to eliminate 'Gharar'. 'Gharar' refers to excessive uncertainty or ambiguity in the terms of the contract or the subject matter, which could lead to disputes. To avoid Gharar in a 'Salam' contract for a future catch of fish, the precise attribute that must be unequivocally specified at the time of contract formation is its detailed descriptive specification, encompassing its species, precise quantity, and specific quality or grade.