In the fish habitat analogy “Perch : fresh water :: ____ : salt water”, which animal best completes the relationship?

Introduction / Context:
This analogy compares a fish and its typical habitat. Perch is a well known example of a fresh water fish, so the pair “Perch : fresh water” expresses the idea “fish type is to its usual environment.” To match this, we must find a creature that stands to salt water in the same way that perch stands to fresh water. This tests your knowledge of common animals and their habitats.

Given Data / Assumptions:

• First pair: Perch and fresh water.
• Second pair: unknown animal and salt water.
• Options: cod, crocodile, snake, frog, turtle.
• We consider typical primary habitats for these animals.

Concept / Approach:
Perch is primarily a fresh water fish found in rivers and lakes. The analogy expects a salt water fish, commonly associated with the sea or ocean, in the second part. Among the options, cod is a well known marine fish that lives in salt water. Other animals listed either live partly on land, in fresh water, or in mixed habitats, so they do not match the pure fish to habitat relationship shown in the first pair.

Step-by-Step Solution:

Step 1: Identify what perch represents. Perch is a fresh water fish species. Step 2: Understand the relationship. The first term is a type of fish, and the second term is its usual water type habitat. Step 3: Apply the same idea to salt water. We need a salt water fish that lives mainly in oceans or seas. Step 4: Look at the options. Cod is famous as a sea fish, caught in oceans and known from dishes like cod fillets. Step 5: Confirm that cod fits “fish that lives in salt water” whereas the other options do not fit as neatly.

Verification / Alternative check:
Check each option quickly. Crocodiles can live in fresh water rivers and sometimes brackish water, but they are reptiles rather than fish. Snakes are land or occasionally water dwelling reptiles, not typical sea fish. Frogs are amphibians associated mostly with fresh water, and turtles can have marine or fresh water species but are reptiles, not fish. Cod is the only option that is both a true fish and strongly associated with salt water in everyday knowledge.

Why Other Options Are Wrong:
Crocodile, snake, frog, and turtle belong to reptile or amphibian groups. Their primary classification is not that of a fish, and their habitats vary widely. The analogy requires a clear parallel with perch as a fish species and its water type. Using a reptile or amphibian breaks this simple species to habitat relation. Only cod preserves both “fish” and “specific water type” in the same way.

Common Pitfalls:
Some learners may choose turtle because sea turtles are famous marine animals, but the analogy is specifically about fish types, not just animals in water. Others may be tempted by crocodile due to its partial association with rivers and estuaries, yet it is again not a fish. Keeping track of both classification and habitat prevents such mistakes in analogy questions.

Final Answer:
The creature that stands to salt water as perch stands to fresh water is the fish cod.