22. A scientist made three observations: (1) in the world's temperate zones, food is more plentiful in the ocean than it is in fresh water; (2) migratory fish in temperate zones generally mature in the ocean and spawn in fresh water; and (3) migratory fish need much nourishment as they mature but little or none during the part of their lives when they spawn. On the basis of those observations, the scientist formulated the hypothesis that food availability is a determining factor in the migration of migratory fish. Subsequently the scientist learned that in the tropics migratory fish generally mature in fresh water and spawn in the ocean.

Which one of the following would it be most helpful to know in order to judge whether what the scientist subsequently learned calls into question the hypothesis?

(A) whether in the world's temperate zones, the temperatures of bodies of fresh water tend to be lower than those of the regions of the oceans into which they flow

(B) whether the types of foods that migratory fish eat while they inhabit the ocean are similar to those that they eat while they inhabit bodies of fresh water

(C) whether any species of fish with populations in temperate zones also have populations that live in the tropics

(D) whether there are more species of migratory fish in the tropics than there are in temperate zones

(E) whether in the tropics food is less plentiful in the ocean than in fresh water

E is the answer.
For the assumption to become hypothesis the scientist needs to know about the pattern of food availability in tropics.

I think it should be B

Correct. You are on the right track.
We have to determine what if found about the latter discovery will weaken the earlier hypothesis.

The conclusion is that food availability is a determining factor for migration among fish. However, if we don't know whether the fish eat the same kind of food, we cannot reach this conclusion.
Lets say the fish change thier foods according to places they migrate, then clearly food cannot the determining factor in migration of fish. This is exactly what B says, that the foods of the fish before and after have to be same. If not, it will weaken the hypothesis.

How does Option E refute the hypothesis ?
If food is less plentiful in the ocean, it justifies/strengthens the hypothesis that fish move from fresh water (more food) to oceans (less food). Isn't it ?

The answer is E

I will go with E, what is the OA?
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Premise (1) Ocean food > fresh water food
(2) migratory fish mature in Ocean BUT spawn in Fresh water
(3) migratory fish eat more food in Ocean > in Fresh water food

Hypothesis: FOOD AVAILABILITY is a determining factor in the migration of migratory fish

BUT the scientist learned that in the TROPICS migratory fish generally mature in fresh water and spawn in the ocean.

Choice B does not say anything about the abundance of food that preferred by TROPICS migratory fish between OCEAN and FRESH WATER. Rather, it only said about KIND OF FOOD => that is irrelevant. You are cheated at this point.

Hope that helps
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