Introduction
Fish and shellfish have been important in human diets for thousands of years. They’re rich in protein, healthy fats, and nutrients, and come in many types and flavors. This guide covers the basics, how to choose them, and tasty ways to enjoy them.
Classification of Fish
1. Open Water Fish
- Habitat: These fish live in the open water of oceans or big lakes, far from the shore and bottom. The water is always moving and there aren’t many places to hide, so the fish need to swim fast and for a long time.
- Body Shape (Streamlined & Torpedo-Shaped)
This shape minimizes water resistance, allowing the fish to swim fast and efficiently across long distances. The body is tapered at both ends, which helps reduce drag.
- Behavior & Adaptation
- Fast swimmers
- Strong tail fins for propulsion
- Constantly moving to find food or avoid predators
Example: Tuna, Mackerel, Swordfish, Sardines, etc.
2. Bottom-Dwellers
- Habitat: These fish live near or on the bottom of oceans, seas, or freshwater bodies like rivers and lakes. The bottom environment is stable and often rich in food but requires camouflage or stealth.
- Body Shape
- Depressed – Flat from top to bottom, perfect for lying on the ocean floor. Example: Flounder, Sole, etc.
- Elongated – Long and thin, making it easy for fish to hide in cracks or dig into the sand. Example, Eel, Gobies,etc.
- Behavior & Adaptation
- Camouflage for hiding from predators or ambushing prey.
- Often have downward-facing mouths for bottom feeding.
- Reduced swimming speed & more stealth-focused.
3. Coral Reef Dwellers
- Habitat: These fish live in coral reefs, which have lots of cracks, hiding places, and other animals. They need to be quick and able to move easily.
- Body Shape
- Laterally Compressed (flattened side-to-side) – This shape enables fish to make quick turns and fit into narrow spaces within coral structures.
- Behavior & Adaptation
- Brightly colored for communication or camouflage within colorful reefs.
- Agile swimmers, often hover in place or dart short distances.
Example: Clownfish, Butterflyfish, Angelfish, Damselfish, etc.
4. Fresh Water Fish (River, Lakes, Streams)
- Habitat: Found in Inland Bodies of Water, which often have changing condition – currents, vegetation, murky waters, and variable temperature.
- Body Shape
- Fusiform – for efficient movement in flowing water (e.g., Trout, Salmon)
- Laterally Compressed – for maneuvering around vegetation (e.g., Sunfish, Bluegill)
- Elongated or Flat-Bottomed – for bottom dwelling or burrowing (e.g., Catfish)
- Behavior & Adaption
- Varied diets and behaviors based on water type (still or flowing)
- Adapted to freshwater conditions like lower salinity
- Often territorial or adapted to smaller spaces than ocean fish
Example: Bass, Pike, Perch, Catfish, etc.
5. Deep-Sea Fish (Abyssal Zone)
- Habitat: These fish live in the deep ocean, where there’s no light, extreme pressure, and little food. It’s a hostile, dark environment requiring special adaptations.
Body Shape: Often soft-elongated or oddly shaped with large mouths and stomachs. They are not built for speed but for survival.
- Behavior & Adaptation
- Bioluminescence – Light producing organs for hunting or mating.
- Large Jaws and Expandable Stomach – to eat rare prey.
- Reduced Bone and Muscle Mass – to conserve energy in low-resource areas.
Example: Anglerfish, Gulper Eel, Viperfish, etc.
Classification of Shellfish
1. Crustaceans
Crustaceans are shellfish with jointed legs and segmented bodies. They usually have hard outer shells and are found in both salt water and fresh water.
Characteristics
- Hard, jointed outer shells.
- Segmented bodies.
- Paired legs, claws, antenna.
- Breathe through gills
Common Habitat
- Oceans, Rivers, and Lakes.
Examples of Crustaceans
- Shrimp – Small, flexible-bodied crustaceans found in oceans and fresh water.
- Prawns – Similar to shrimp, often slightly larger with gill and leg difference.
- Crabs – Broad, flat bodies with a pair of claws and sideways movement.
- Lobster – Large marine crustaceans with powerful claws and muscular tails.
- Crayfish – Fresh species resembling small lobster.
- Krill – Tiny shrimp like creatures, important in marine food chains.
2. Mollusks
Mollusks are soft-bodied invertebrates, most of which have calcium carbonate shells. They can be further classified into three main subgroups:
Univalves
It is a kind of Mollusks with a single coiled shell. It is often used interchangeably with “Gastropod“.
Characteristics
- Move using a muscular foot
- Often have a spiral shell
- Feed using a tongue like organ with tiny teeth
Examples:
- Snails – Marine and fresh water, have coiled shells.
- Whelks – Sea snails, often carnivorous.
- Periwinkles – Small marine snails found on rocky shores.
- Abalone – Flattened, ear-shaped shells with a row of breathing holes.
Bivalves
The bivalve is a type of mollusks characterized by having a shell composed of two separated halves that are hinged together.
Characteristics
- Filter feeders
- Shells joined by a ligament and hinge
- Often burrow in sand or attach to surface
Examples:
- Clams – Burrowing shellfish found in sandy or muddy bottoms.
- Oysters – Filter feeders often farmed for food and pearls.
- Mussels – Live attached to rocks, have dark blue or black shells.
- Scallops – Can swim by clapping their shells together.
Cephalopods
Highly intelligent mollusks with no external shell and arms or tentacles. They have only one internal shell called a “Pen“.
Characteristics
- Having good eyesight and nervous system
- Can squirt ink for defense
- Masters of camouflage
Examples:
- Octopus – Eight arms, no shell, highly intelligent.
- Squid – Ten arms (including two tentacles), internal shell i.e. Pen.
- Cuttlefish – Similar to squid but with a broader body and a cuttlebone.
- Nautilus – Has a coiled external shell and many small tentacles.