Ichthyology: Study of Fishes

• Ichthyology is the scientific study of fishes.

Common Terminologies

• Anadromous: Fish live mostly in the ocean but breed in fresh water.
• Amphidromous: Fish move between fresh and salt water during their life cycle, but not to breed.
• Catadromous: Fish live in fresh water and breed in the ocean.
• Diadromous: Fish travel between salt and fresh water.

Industry

• Aquaculture in the Philippines has a long history involving diverse species and farming practices across various ecosystems.

Marine Resources

• Total Territorial Water Area: 2,200,000 sq. km.
• Shelf area (Depth 200m): 184,600 sq. km.
• Coral Reef Area: 27,000 sq. km.
• Coastline (Length): 36,289 km.

Inland Resources

• Swamplands: 246,063 ha
• Brackish water Fishpond: 253,854 ha
• Other Inland Resources: 250,000 ha

Fish Production

• Ranked 5th in fish production with 5.16 million MT of fish, crustaceans, mollusks, and aquatic plants, constituting 3.06% of global production.
• Ranked 10th in aquaculture production of fish, crustaceans, and mollusks, contributing 1.24% to total global aquaculture production.
• The country's aquaculture production is valued at over 1.58 billion dollars (FAO website).
• It is the top 3 largest producer of aquatic plants, totaling a production of 1.80 million metric tons, ≈ 9.48% of total world production.

Systems of Culture

• Freshwater Culture
  • Cultivation in freshwater environments like reservoirs, rivers, and groundwater where salinity ≤ 0.5%.
  • Early life stages may occur in brackish or marine waters.
• Brackish water Culture
  • Cultivation in brackish water environments like estuaries and lagoons, with salinity fluctuating between 0.5% and full seawater strength.
  • If conditions do not affect cultural practices, classify production as "Freshwater culture" or "Mariculture."
  • Early life stages may occur in fresh or marine waters.
• Mariculture
  • Cultivation in seawater environments like fjords and open waters where salinity generally exceeds 20%.
  • Earlier life stages may occur in brackish water or freshwater.

Growing Units

• Ponds and Tanks
  • Artificial units above or below ground level to hold and interchange water, with a low rate of exchange (≤ 10 changes per day).
• Enclosures and Pens
  • Water areas confined by barriers allowing uncontrolled water interchange, occupying the full water column between substrate and surface.
• Cages
  • Open or covered structures constructed with porous material allowing natural water interchange, which may be floating, suspended, or fixed to the substrate.
• Raceways and Silos
  • Artificial units above or below ground level for high rates of water interchange, exceeding 20 changes per day.
• Barrages
  • Semi-permanent or seasonal enclosures formed by impervious man-made barriers and natural features.
• Rice-cum-fish Paddies
  • Paddy fields used for culturing rice and aquatic organisms.
• Rafts, Ropes, Stakes
  • Structures for culturing shellfish and seaweeds in open waters, with stakes impaled in intertidal areas and ropes suspended in deeper waters.
• Hatcheries
  • Installations for breeding, nursing, and rearing seed of aquatic organisms from fry to juvenile stages.
• Nurseries
  • Refers to the second phase in the rearing process of aquatic organisms in small.

Culture Species

• The common aquaculture species in the Philippines are:
  • Seaweed (Kappaphycus and Eucheuma spp.).
  • Milkfish (Chanos chonos).
  • Tilapia (Oreochromis niloticus).
  • Shrimp (Penaeus monodon).
  • Carp (Aristichthys nobilis).
  • Oyster (Crassostrea iredalei).
  • Mussel (Perna viridis).

Fish Anatomy

• Fish are aquatic vertebrates covered with scales, equipped with paired and unpaired fins.
• Most fish are ectothermic, their body temperatures changing with ambient temperatures.
• Fish diversity: 31,500 species.

External Anatomy

• Scales
  • Most fish have scales.
  • Sharks have dermal denticles that feel like sandpaper.
  • Bony fish scales made of bone look like shingles.
  • Types of scales: Placoid, Cycloid, Ptenoid, Ganoid
• Fins
  • Move, stabilize, and protect fish.
  • Paired fins: pectoral and pelvic fins
  • Unpaired fins: anal, caudal, and dorsal fins
  • Some fish lack certain fins.
  • Bony fish fins have visible rays and spines.
  • Cartilaginous fish fins not visible.
  • Fins are fairly stiff.
• Dorsal Fin
  • Located along the back, providing stability for swimming in a straight line.
• Caudal Fin (tail fin)
  • Responsible for sudden forward movement, swimming patterns, slowing down, and turning.
• Anal Fin
  • Located on the ventral surface, providing stability and preventing rolling.
• Pectoral Fins
  • Paired fins near gill openings provide stability, hovering, slow turns, navigation, and constant motion.
• Lateral Line
  • Located on both sides, composed of neuromasts that detect vibrations through cilia in fluid-filled canals.
  • Helps fish locate objects and perceive surroundings.
• Skin or Integument
  • First barrier of defense and responsible for maintaining osmotic integrity, waterproofing, and armor plating,
  • Rapid water logging in freshwater and dehydration in saltwater if abrasion occurs.
  • Composed of 2 layers: Epidermis (outer) and Dermis (inner).
  • Mucus layer: protective and slimy.
  • Capable of binding irritating particles like parasites, bacteria, and heavy metals.
• Pigment Cells
  • Colors are produced by cells in the dermis.
  • Fish can change color during mating, as a survival tactic, and during feeding times.
  • Melanin grains disperse to darken fish and tighten to lighten.

Internal Anatomy

• Circulatory System
  • Two chambers: atrium and ventricle.
  • The venous side of the heart is preceded by the sinus venosus and arterial side is followed by bulbus arteriosus.
• Respiratory System
  • Gills are the respiratory organs where oxygen is removed by diffusion in the blood.
• Life Support Systems
  • Water passing across the gills is where oxygen enters the fish's blood through diffusion
  • The Oxygen that the fish "breathe" is dissolved in enters the water at the surface by diffusion and as a byproduct of photosynthesis by aquatic plants.
• Swim Bladder
  • Evolved from the lung.

Tilapia

• Tilapias belong to the Cichlidae family, including Oreochromis, Tilapia, and Sarotherodon.
• Nile Tilapia (Oreochromis) is popular due to hardiness, disease resistance, ease of breeding, growth rate, taste, and environmental tolerance.
• Mozambique tilapia (Oreochromis mossambicus) was introduced in 1950, but Nile tilapia brought better commercial production in the early 1970s.
• Most tilapia production is from freshwater ponds and cages.
  • Yields 4-8 tones/ha/crop are obtained
• In 100 m2 floating cages, 67/m2 of Nile tilapia fingerlings are stocked and after feed they weigh 175 g
• Central Luzon tilapia farming is free from disease problems. Most mortalities are caused by environmental conditions and poor husbandry
• Sex identification:
  • Males have two openings in front of the anal fin (anus and urogenital pore).
  • Females have three openings (anus, genital pore, and urinary pore).
  • The genital papilla is usually smaller in the female.
  • Tilapia can be sexed at 15 grams.
  • Sexes can be readily distinguished by rubbing ink along the papillae of the tilapia.
• Spawning: Male excavates nest in pond and mates with females
  • the female spawns two to four eggs, the eggs are fertilized, incubated in her mouth until they hatch.
  • The male protects round nest (diameter 30-60 cm) , the eggs are fertilized by the male and collected by the female for incubations
  • The eggs are yellow in color and hatch in about five to seven days.
• Feeding Habits: Newly hatched fry depend on their yolk sacs until consumed. Then, they eat the smallest phytoplankton.
  • As the fry become bigger, they eat larger organisms and supplemental feeds such as ricebran, fishmeal and others
  • Tilapia feed on a variety of phytoplankton as their primary food items.
  • Oreochromis niloticus has firm pharyngeal teeth set on a triangular blade that prepares the food for digestion.
• Salinity Tolerance:Tilapias are relatively euryhaline and can tolerate sea water
  • spawning is suppressed at salinities between 15 and 35 parts per thousant
  • Oreochromis massambicus can tolerate salinity changes much better than Oreochromis niloticus, and can reproduce at high salinities.
• Parameters are
  • Temperature (25-300c) Optimum for reproduction and growth
  • Salinity (10-15 ppt) Favors growth
  • pH (6.5-9) Optimum for primary reproduction.
  • C02 (20 mg/L) Silt may injure
  • Turbidity (30-35) For intensive culture flow-through system
  • Water current (20)

Bangus (Milkfish)

• Milkfish is cultured in brackish water ponds, freshwater lakes, shallow bays, and sea-based cages and produced under wide range of environment and culture systems
• yields only 500 kg per hectare, to marine cages capable of harvesting as much as 50,000 kg in an area as is the case with milkfish
• Production comes from brackish water fishponds.
• Adults are well developed, migratory, large and mature sexually in 5 years and only spawn in fully saline waters.
• Activity correlated with the new or full moon phases, takes place mostly in the night.
• The spawning takes place near coral reefs during the warm months of the year, and populations near the equator spawn year-round.

Shrimp

• Shrimp farming in the Philippines uses a variety of systems which are affected by climate and the cost of farm inputs.
• Shrimp farming follows traditional, semi intensive and intensive system.

Fish Behavior

• It is the action of a fish in response to its environment including other animals.
• Migration: It is to escape cold temperatures or to find food.
• Schooling: School is a group of fish of the same size and species moving in the same direction.
• Aggression: It is usually associated with reproduction and defense of feeding territory.
• Resting: Fish spend a good portion of their day or night resting
• Communication: The means of visual communication is Body movements, postures, colors, color patterns and light.
• Cleaning: Some fish are Cleaners that pick parasites from other fish.

Fish Reproduction

• Fish have come up with three modes of reproduction depending on the method they care for their eggs.
• Modes of Reproduction
  • Oviparity: Lay undeveloped eggs, External fertilization, Internal fertilization
  • Ovoviviparity: Internal development- without direct maternal nourishment- Advanced at birth
  • Viviparity: Internal development- direct nourishment from mother-Fully advanced at birth

Parental Care

• In fishes, parental care is very rare as most fish are broadcast spawners
• Nile tilapia are sexually mature within 6 months and are easy to breed.
• requires a surface upon which the female deposits eggs, the eggs are fertilized externally by release Of sperm from the male

Blood Flow and Counter Current Exchange

• The blood flows thorough the gill filaments and Secondary lamellae in the opposite direction from the water passing the gills.
• Important for getting all of the available oxygen out of the water and into the blood.

Classification of Fish

• Modern fish are divided into three classes.
  • AGNATHA- primitive jawless fish
  • CHONDRICHTHYES- the jawed fish with cartilaginous skeletons
  • OSTEICHTHYES- fish with bony skeletons

Health Management

• Disease is health abnormality displayed by living organisms through specific or nonspecific sign.
  • Host can be resistant or susceptible to a given disease.
  • Pathogen Agents can be classified into physical, chemical and biological.
  • Environment is composed of water and its holding system like tanks, ponds, cages, pens, etc.

Water Quality Management

• Stress in Disease Development
  • Alarm stage
  • Adaptive stage
  • Exhaustion stage
• Disease Diagnosis
• recognizing the occurrence of an abnormality and identifying its cause.

Disease Signs

• Reduced feeding
• Abnormal changes in fish color and behavior
• Separation from the school
• Abnormal swimming behavior
• Loss Of equilibrium
• Lesions may be observed

Common Diseases

• Fish Diseases caused by Parasites
  • Ciliate Infestation - Ichthyophthiriasis, Cryptocaryonosis, Trichodiniosis
  • Flagellate infection - Amyloodiniosis, Velvet Disease
  • Myxosporean Infections
  • Microsporidian Infections
  • Monogenean Infestation - Skin monogeneans, Gill monogeneans Digenean Infestations
  • Cestode Nematode
  • Acantocephalan Infection
• Crustacean Infestation
  • Argulus or Freshwater Louse infestation
  • Caliguid or Sea Louse Infestation
  • Lernaeid Infestation Isopod (Timod) Infestation
• Fungal Diseases - The fungal pathogen infecting fishes and include representatives of three major groups
  • the straminipolous organisms (zoosporic fungi)
  • Deuteromycetes
  • Ascomycetes.
• Bacterial Diseases: Most bacterial disease agents are part of the normal microflora and are generally considered as secondary or opportunistic pathogens
  • Columnaris disease
  • Edwardsiella septicemia or Edwardsiellosis
  • Vibriosis
  • Aeromonas infections
  • Pseudomonas septicemia or Red spot disease
  • Streptococcal Infection
  • Nocardiosis