Introduction to Fish
Fish (Le Poisson) are cold-blooded, gill-breathing aquatic animals belonging to the group Pisces. They live in water, use fins for movement, and do not have true limbs, feet, toes, or fingers. Their streamlined bodies and gills make them perfectly adapted for aquatic life.
In culinary terms, fish and shellfish together are called seafood. Even if they come from rivers, lakes, ponds, or fish farms, the term “seafood” is still commonly used because the category broadly includes all edible aquatic species.
- Fish holds a distinct position in classical French cuisine, where it appears as a separate course called “Poisson.”
- Depending on body structure:
- Flat fish yield 4 fillets
- Round fish yield 2 fillets
Fish is considered one of the healthiest animal proteins because:
- Low in fat (especially saturated fat)
- High-quality complete protein
- Rich in Omega-3 fatty acids
- Contains vitamins D, B2 (Riboflavin), B12
- Excellent source of iodine, calcium, phosphorus, iron, zinc, magnesium, potassium
Regular fish consumption is linked to:
- Better heart and brain health
- Reduced blood pressure
- Lower risk of heart attack and stroke
Nutritional Value of Fish
Values vary slightly by species, fat content, and habitat (lean vs oily fish).
Below , nutritional Value (Approx. per 100 g of raw edible fish) is presented in table:
| Component | |
|---|---|
| Energy | 90–200 kcal |
| Protein | 18-21 g |
| Fat | 1–12 g (lean fish lower, oily fish higher) |
| Omega-3 Fatty Acids | 0.5–2.5 g |
| Water | 60-80% |
| Calcium | 10–50 mg |
| Phosphorous | 150–250 mg |
| Iron | 0.5–2 mg |
| Iodine | Varies, higher in marine fish |
| Vitamin D | 5–25 µg |
| Vitamin B12 | 0.1–0.3 mg |
Lean fish (e.g., cod, sole) = low fat, lower calories
Oily fish (e.g., salmon, mackerel) = higher fat, richer in Omega-3
Classification of Fish
Fish are scientifically classified based on their body structure and evolution into three main groups:
- Agnatha – Jawless Fish
- Chondrichthyes – Cartilaginous Fish
- Osteichthyes – Bony Fish
- Agnatha
These are considered the most primitive of all fish. They look almost eel-like and lack many features found in other fish.
Example: Lampreys, Hagfish
Characteristics:- No jaws (mouth is round and sucker-like)
- No paired fins
- No true stomach
- Cartilaginous internal support, but not a full skeleton
- Smooth, scaleless skin
- Multiple gill pouches (usually 7 or more)
- Feed by attaching to other animals and sucking blood or tissue
- Chondrichthyes
These fish have skeletons made of cartilage instead of bone, making them lighter and more flexible. This group includes some of the ocean’s top predators.
Example: Sharks, Rays, Skates, Sawfish
Characteristics:- Mostly marine species
- Well-developed jaws
- Ventral mouth (located on the underside)
- Cartilaginous skeleton, strengthened with calcium
- No swim (air) bladder, so they must keep swimming to stay afloat
- Predatory feeding habits (prey on fish and marine animals)
- Two-chambered heart (one auricle, one ventricle)
- Body often covered with placoid scales (tooth-like)
- Osteichthyes
This is the largest and most diverse fish group. Nearly all fish used in cooking, hotels, and food service belong here.
Characteristics:- Endoskeleton made of bone
- Found in both freshwater and marine environments
- Terminal mouth (at the front of the head)
- Paired fins
- Jaws present
- Skin covered with bony/scaly plates containing mucous glands
- Swim bladder present, helping them float and control buoyancy
Osteichthyes are further sub-divided into 2 group:
- Ray- finned fish
Examples: Salmon, Carp, Cod, Snapper, Tuna, Mackerel, Lizardfish- Fins supported by thin, flexible bony rays
- Make up the majority of commercial fish
- Culinary staples worldwide
- Lobe-finned fish
Example: Lungfish, Coelacanth- Fins are fleshy and muscular, supported by bones
- Very few species exist today
- Rarely used as food
| Summary Table | Agnatha | Chondrichthyes | Osteichthyes |
|---|---|---|---|
| Skeleton Type | Primitive cartilage | Cartilage | Bone |
| Jaws | No | Yes | Yes |
| Paired fins | No | Yes | Yes |
| Habitat | Mostly aquatic/parasitic | Mostly marine | Marine & Freshwater |
| Culinary Use | Very low | Moderate | Very high |
Classification on Basis of Environment / Habitat
Fish can also be grouped according to the type of water they live in. The two primary categories are:
- FreshWater Fish
Freshwater fish spend all or most of their lives in rivers, lakes, ponds, and streams where the salinity is less than 1.05%.
Example: Rohu, Catla, Singhara, Calbasu, Malli, Trout, Carp, etc.- Live in low-salt environments.
- Generally leaner because they swim more and often move against currents.
- Some species can migrate between fresh and salty water (e.g., during breeding).
- Marine (Sea) Fish
These fish live in saltwater oceans and seas and are adapted to high salinity.
Example: Tuna, Mackerel, Cod, Snapper, Pomfret, Shark, Sardine, etc- The salt-rich water provides buoyancy, so they require less effort to stay afloat.
- Many species are richer in natural oils, including Omega-3 fatty acids, which support heart health.
- Often have a stronger flavor compared to freshwater fish.
On the basis of Bodily Form / Physical shape
Fish can also be grouped according to the shape of their body, and there are two main forms:
- Flat Fish
Flat fish have a flattened, oval body and both eyes are usually on one side of the head. They swim and rest lying flat along the seabed.
Example: Sole, Halibut, Flounder, Turbot, Plaice- Flat and asymmetric body
- 4 fillets (two on each side – top and bottom)
- Live mostly at the bottom of oceans or rivers
- Generally less colorful
- Often more expensive due to harder catch
- Many species are lean, with low fat content (usually below 1.5%)
- Most fat and vitamins A & D are stored in the liver
- Fewer visible scales
- Round Fish
Round fish have a rounded, cylindrical body and an eye on each side of the head. They swim in a vertical position and move freely in open water.
Example:
Lean Round Fish: Cod, Haddock, Bass, Pollock
Fatty Round Fish (higher fat up to ~20%) : Salmon, Mackerel, Tuna, Sardine, Herring- Round, fuller body shape
- 2 fillets (one on each side)
- Live in mid-water or near the surface
- More colorful and widely available
- Generally less expensive than flat fish
- Can be lean or fatty (fat content varies by species)
- In fatty species, vitamins A & D are stored in the flesh
Differences between Flat fish and Round Fish
| Basis | Flat Fish | Round Fish |
|---|---|---|
| Eyes | Both on one side (usually) | One on each side |
| Body Shape | Flat, oval, asymmetrical | Cylindrical / rounded |
| Fillet Yields | 4 fillets | 2 fillets |
| Color | Usually dull/less colorful | Often more colorful |
| Fat content | Generally lean | Varies: lean or fatty |
| Scales | Fewer noticeable scales | Generally more scales |
| Fat storage | Mostly in liver | In flesh (fatty species) |
Quality Points of Fish
- Eyes
- Should be bright, clear, full, and bulging
- Not dull, cloudy, or sunken
- Smell
- Should have a clean, mild sea or river smell
- No unpleasant, sour, or ammonia-like odor (ammonia develops as bacteria break down the fish)
- Body Shape / Rigidity
- The fish should appear firm, well-shaped, and not floppy.
- A freshly caught fish often shows slight rigor mortis (stiffness) — this is a good sign of freshness.
- Color of Flesh
- Flesh should be translucent, moist, and bright, not dull or dry.
- Discoloration, browning, or yellow patches indicate age or oxidation.
- Bloodliness
- If visible, the blood along the spine or gills should be bright red, not brown or black.
- Dark or dried blood signals old fish.
- Gills
- Deep pink to bright red in color
- Moist and clean, not brown, grey, or slimy
- Scales & Skin
- If it’s a scaly fish, the scales should be plentiful, tight, and firmly attached
- Skin should look shiny and metallic, not dry or patchy
- Flesh Texture
- Flesh should be firm, elastic, and spring back when pressed
- Should not feel soft, mushy, or leave an indentation
- Belly / Gut Area
- Belly should not be torn, swollen, or sagging
- If opened, the internal organs should appear clean and intact, not ruptured or foul-smelling
- Flesh Attachment
- Flesh should cling firmly to the bones
- Should not separate or flake off easily
- Tail & Fins
- Tail should be stiff and firm, not limp or dried out
- Fins should look moist and undamaged
- Surface Mucus
- Fresh fish has a thin, clear, slippery natural mucus layer
- Should not be thick, sticky, or milky
Cuts of Fish
- Fillet
A fillet is a boneless cut obtained by making a horizontal cut along the backbone, removing the flesh from the side of the fish. This cut can be taken from both round and flat fish.
· Round fish yield 2 fillets
· Flat fish yield 4 fillets
Fillets generally run the full length of the fish and are prized for their tenderness and ease of cooking. In some kitchens, the upper portion may be referred to as the top loin or back loin.
Characteristics:- Minimal or no bones
- Even thickness; easy to portion
- Versatile and commonly used in restaurants
Suitable Cooking Method: grilling or barbecuing, pan-frying or shallow-frying, poaching, steaming, deep-frying, or sautéing
- Darne (Steak Cut of Round Fish)
A darne is a thick, cross-sectional slice cut perpendicular to the spine from a large round fish. It is cut through the bone, so the central spine remains attached.
· Typical thickness: 2–3 cm
· Shape resembles a steak
· Commonly produced from large species like salmon, tuna, or kingfish
Characteristics:- Contains bone
- Firm structure; holds shape during cooking
- Ideal for hearty preparations
Suitable Cooking Methods: Grilling, Barbecuing, Pan-frying, Poaching, Baking, Indian-style curries / stews
- Supreme (Portioned Fillet)
A supreme is a small, neatly trimmed diagonal cut taken from a large fillet. It is completely boneless and considered one of the finest portions of fish due to its uniform shape, tenderness, and premium presentation. Supremes are also referred to as pavé in some kitchens.
Suitable Cooking Methods: Grilling, pan-frying, or poaching - Goujan (Finger Fish)
A goujon is a fillet cut into narrow strips measuring roughly 6 × 1 × 1 cm, similar in size and shape to a finger. It is mainly used for small portions, snacks, garnishes, or finger foods.
Suitable cooking methods: Goujons are most commonly shallow-fried or deep-fried, and they can also be baked or sautéed for light and crispy preparations. - Paupiette
A paupiette is a thin slice of fish fillet that is stuffed, rolled into a cylinder, and secured with string to maintain its shape. The stuffing may include vegetables, herbs, seafood, or even fruits. Paupiette is also recognized as a classic French preparation where thin fish slices like sole, whiting, tuna, or anchovy are rolled and cooked gently.
Suitable cooking methods: Paupiettes are usually poached, steamed, or baked, as these gentle methods help retain the roll’s structure and keep the fish moist and delicate. - Tronçon (Steak of Flat Fish)
A tronçon is a thick, bone-in steak cut taken from a flat fish such as halibut, sole, turbot, or flounder. It is essentially the flat-fish equivalent of a darne, usually around 4–5 cm thick, with the backbone in the center.
Suitable Cooking Methods: Grilled, baked, poached, or shallow-fried - Pavé
A pavé resembles a supreme but is rectangular in shape and often left with the skin on, giving it a clean, restaurant-style presentation. It is thick and uniform, making it suitable for precision cooking.
Suitable Cooking Methods: Pan-fried or sautéed - Goujonette
A goujonette is a smaller, thinner version of a goujon. It is cut into very fine strips—around 3–4 cm long and about 0.5 cm thick—making it delicate and bite-sized. Because of its small size, it is mostly used for garnishes, canapés, or light appetizers.
Suitable Cooking Methods: Goujonettes cook very quickly and are usually deep–fried or shallow-fried to achieve a crisp texture. They may also be baked for a lighter preparation. - Medallion
A medallion is a neat, round, boneless slice taken from a large fish fillet. It has a uniform thickness and circular shape, which allows even cooking and an elegant plate presentation. Medallions resemble small fish “steaks” but without bone.
Suitable cooking methods: Best prepared by poaching, pan-frying, grilling, or baking, as these methods help maintain shape and tenderness. - Mignon
A mignon is a small portion of fish fillet that is folded into a cornet or triangular shape, giving height and a refined appearance. This cut is commonly used in fine dining, where visual presentation is important.
Suitable cooking methods: Gentle cooking methods such as steaming, poaching, or baking are preferred to help the folded shape remain intact and prevent the fish from drying out. - Délice
A délice is a small fillet—often from flat fish like sole or flounder—that is folded inward on both sides to create a compact portion. It may also be filled with ingredients such as herbs, vegetables, or seafood, making it suitable for elegant stuffed preparations.
Suitable cooking methods: Poached, steamed, or baked - Butterfly / Cutlet
A butterfly cut, also known as a cutlet, is made by slicing one side of the fish from behind the head down toward the tail and opening it out like wings. This creates a connected “double fillet” without a central bone, resulting in a larger, symmetrical portion.
Suitable Cooking Methods: Grilling, pan-frying, baking, or barbecuing
Preservation of fish
Fish is one of the most perishable foods because it has high moisture, delicate flesh, and rapid bacterial activity. Once a fish dies, enzymes and microorganisms begin to break down the flesh, causing spoilage, off-odors, and texture changes. Therefore, preservation methods are used to extend shelf life, maintain quality, and ensure safety.
The basic aim of preservation is to slow down or stop the growth of bacteria, enzymes, and chemical reactions that cause spoilage.
- Chilling or refrigeration
- Fish is kept close to 0°C or stored on ice.
- Suitable for short-term storage (about 2–3 days).
- Fish should be cleaned, gutted, and covered properly.
- Freezing
- Stored at –18°C or lower.
- Can preserve fish for several months.
- Helps maintain taste and nutrients.
- Airtight packing prevents freezer burn.
- Commonly used for fillets, steaks, prawns, and packaged seafood.
- Drying
- Removes moisture so bacteria cannot grow.
- Can be sun-dried, air-dried, or machine-dried.
- Traditional method in many regions.
- Examples: dried anchovies, stockfish, sukuti.
- Salting
- Salt draws out moisture from the fish.
- Can be dry salted or brined.
- Sometimes used with acids for pickling
- Smoking
Smoking preserves fish by exposing it to smoke, which adds flavor and slows bacterial growth. It is usually done after salting or brining.- Two types: cold smoking and hot smoking.
- Cold smoking is done at 20–30°C where the fish is not cooked but only smoked, usually after curing or salting; it gives a soft, silky texture with mild smoke flavor and requires refrigeration, examples being cold-smoked salmon and haddock.
- Hot smoking is done at 60–80°C where the fish is cooked while smoking, producing a firm, flaky texture with strong smoky flavor; it is ready to eat after smoking and examples include hot-smoked mackerel, trout, and tuna.
- Pickling
Pickling preserves fish by soaking it in a solution of salt, vinegar, and sometimes spices, which prevents bacterial growth and enhances flavor.- Adds a tangy, appetizing taste.
- Can be stored under refrigeration for several weeks.
- Common examples: pickled herring, vinegar-marinated fish.