Fish

Basic Fish Anatomy

Major Systems

Integumentary system (skin and scales)

• Cycloid scales: smooth, rounded (carp, tetras, salmonids)
• Ctenoid scales: with teeth along the posterior edge (Perciformes, Cichlidae)
• Ganoid scales: hard, do not overlap (primitive fish: polypterids, spadefish)
• Scaleless: catfish (barbs, corydoras), eels
• The skin produces mucus that protects against pathogens and reduces friction

Respiratory System

• The gills exchange O2 and CO2 with the water
• Water flow: mouth → pharynx → gills → operculum
• Labyrinth fish (Betta, Gourami): a labyrinth organ that allows them to breathe atmospheric air
• Electric fish, lungs: Some species can breathe partially out of the water

Lateral system (lateral line)

• Detects vibrations and changes in water pressure
• Essential for moving in schools, detecting predators and prey
• It is damaged by contaminants, chlorine, and sudden temperature changes

Swim bladder

• Hydrostatic device that controls buoyancy
• When the gas flow is adjusted, the fish rises or sinks without swimming
• Problems: "swim bladder disease" — fish that swim on their sides or cannot submerge themselves

Digestive System

• Varies depending on the diet:
  • Carnivores: short intestine, powerful stomach
  • Herbivores: long intestine (to break down cellulose)
  • Omnivores: intermediate

---