Which of the following animals is correctly classified as a true fish?

Introduction / Context:
Common names of animals can be misleading, especially when they include words like fish while the animal belongs to a different group. In zoology and general biology, it is important to know which animals are true fishes and which belong to other groups such as mammals or invertebrates. This question tests your ability to correctly identify a true fish among several aquatic or marine animals, some of which have fish in their common names.

Given Data / Assumptions:

• The options include jelly fish, lobster, salmon, and whale.
• All listed animals live in water, but they belong to different taxonomic groups.
• We assume basic knowledge of vertebrates versus invertebrates and mammals versus fishes.

Concept / Approach:
True fishes are aquatic vertebrates that typically have gills throughout life, fins, and scales, and belong to classes such as Osteichthyes (bony fishes) and Chondrichthyes (cartilaginous fishes). Salmon is a bony fish and fits this definition. Jelly fish are invertebrates belonging to the phylum Cnidaria and do not have a backbone or typical fish anatomy. Lobster is a crustacean, an invertebrate arthropod. Whales are mammals that breathe air through lungs, give birth to live young, and nurse them with milk. Therefore, only salmon is correctly classified as a true fish.

Step-by-Step Solution:
Step 1: Identify that salmon is a well known example of a bony fish, used as food and known for migration. Step 2: Recall that jelly fish are gelatinous, radially symmetrical invertebrates from the phylum Cnidaria, not true fishes. Step 3: Recognise that lobster is a crustacean arthropod with a hard exoskeleton and jointed legs, not a vertebrate fish. Step 4: Remember that whale is a marine mammal with lungs and mammary glands, not a fish. Step 5: Select salmon as the correctly classified true fish among the options.

Verification / Alternative check:
Taxonomy references list salmon under class Actinopterygii within the bony fishes. Jelly fish appear under phylum Cnidaria, class Scyphozoa or related groups, lobster under phylum Arthropoda, class Crustacea, and whales under phylum Chordata, class Mammalia. These classification details clearly show that salmon is the only option that fits the fish category. Field guides and environmental literature also consistently refer to salmon as a fish species, while making clear that whales are marine mammals.

Why Other Options Are Wrong:

• Jelly fish: Despite the name, jelly fish is not a true fish and is an invertebrate cnidarian.
• Lobster: This is a crustacean arthropod with an exoskeleton and jointed appendages, not a fish.
• Whale: Whales are marine mammals, warm blooded vertebrates with lungs and live birth, not fishes.

Common Pitfalls:
A common mistake is to rely on everyday language and assume that any animal with fish in its name must be a fish. Examples such as starfish, cuttlefish, and jelly fish show that this is not reliable. Another pitfall is to think that any aquatic animal is a fish. Remember that many different groups, including mammals, reptiles, and invertebrates, have members that live in water. For exam purposes, focus on anatomical and taxonomic definitions rather than common names alone.

Final Answer:
Among the given options, the animal that is a true fish is salmon.