Fish Nutrition and Feeding Study Guide

Fish Nutrition and Feeding

Learning Objectives

• Understand the differences between nutrition and feeding of fish and land animals.

• Understand fish digestive system.

• Physical properties of feedstuff that facilitate feeding in water.

• Understand the consequences of over-feeding fish.

• Feed management.

Natural Dietary Habits and Digestive Tract Morphology

• There are over 18,000 species of fish and lower chordates identified.

• Seasonal feeding patterns: Influenced by the winter season.

• Feeding behaviors in water can be classified into three main dietary habits:

  • Carnivorous: Flesh-eating fish.

  • Omnivorous: Fish that eat both plants and animals.

  • Herbivorous: Plant-eating fish.

  • Opportunistic: Consume whatever is available.

• Challenges in fish nutrition include:

  • Environmental factors

  • Availability of food sources

  • Digestive efficiency

Unique Features of Fish Digestive System

• The fish digestive system consists of several key components:

  • Mouth: As the entry point for food.

  • Oesophagus: Transports food to the stomach.

  • Stomach: Varies by species; important in nutrient breakdown.

  • Pyloric ceca: Extensions from the intestine aiding in digestion.

  • Intestine: Main site of nutrient absorption.

  • Primary kidney: Involved in excretion.

  • Rectum & Anus: Final part of the digestive tract.

Digestion and Nutritional Needs of Specific Fish Species

• Rainbow trout: Carnivorous with a complex digestive system.

• Catfish: Omnivorous with a punched stomach, allowing for different feeding habits.

• Carp: Omnivorous with no stomach, utilizing a digestive approach suitable for their diet.

• Milkfish: Microphagous planktivore with a tubular stomach and muscular gizzard.

Unique Physiological Traits of Fish

• Fish are poikilothermic (cold-blooded), relying on environmental temperatures for metabolic activities.

• Ammonia is excreted as the main nitrogenous waste product.

• Fish do not expend energy resisting gravity, allowing more energy use for growth.

• Some minerals can be absorbed through the gills, skin, and oral epithelium, which reduces the necessity for supplementation.

Fish Nutrition

• The nutritional needs of fish are calculated as 1.2 to 3.0% of body weight (BW).

• Conversion of energy to body tissue is notably efficient, averaging 1.5 to 2.0 lb. of feed to achieve 1 lb. of fish gain.

• Energy demands are affected by:

  • Physical activity levels

  • Water temperature

  • Body size

  • Stress levels

Water Temperature and Feeding Rates

• Optimal feeding temperatures range between 25° to 30° C.

• Monthly fish population counts are necessary to adjust feeding rates accordingly.

• Proper adjustments in feed can significantly impact growth and health.

Nutritional Composition of Fish Feeds

• Fish rations typically contain 32 to 47% crude protein.

• Essential fatty acids, including omega-3 fatty acids (linolenic and linoleic acid), are vital, as deficiencies can retard growth, increase mortality, and induce physical deformities.

• Fish can digest carbohydrates, but many cannot synthesize Vitamin C, leading to deficiencies characterized by:

  • Defective connective tissue synthesis

  • Structural deformities

  • Ascites (abnormal fluid collection)

  • Hemorrhage

• A recommended intake of Vitamin C is between 25 to 50 mg/kg of air-dry diet.

Colorful Nutrients

• Carotenoids are necessary for fish health, derived from sources like:

  • Zooplankton: Contains crucial carotenoids.

  • Astaxanthin and Canthaxanthin: Key carotenoids that affect coloration and health.

  • The absorption of these nutrients varies between different fish species.

• Other sources of carotenoids include lutein and zeaxanthin, found in yellow corn, dehydrated alfalfa meal, or algae.

Feeding Guidelines for Different Fish Species

Least Cost Formulation Restrictions for Fish Feeds

• Example calculations based on fish weight and feeding frequency for:

  • Channel catfish

  • Common carp

  • Nile tilapia

(Additional data table content is included in original text with feeding rates at different weights)

Adjustments Based on Temperature

• Feed allowances should be modified according to water temperature, measured at 50-cm depth:

  • At ≤15°C: Feed at 1% rate 1x/day (max. 3x/week)

  • At 16°-19°C: Feed at 60% of calculated allowance 1x/day every day

  • At 20°-24°C: Feed at 80% of calculated allowance 1 or 2x/day every day

  • At 25°-29°C: Feed at 100% of calculated allowance daily

  • At 30°-32°C: Feed at 80% of calculated allowance

  • At >33°C: Feed only what fish will actively consume, as such temperatures should be avoided.

Larval Fish Feeding Needs

• Larval fish have immature digestive systems lacking:

  • Enzymes

  • Hormones

  • Growth factors typically found in live foods.

• Live foods such as zooplankton are crucial for larval nutrition.

• The size of pellets should not exceed 20% of the mouth opening. Frequent feeding is required due to their high metabolic rates:

  • 10 to 24 times per day.

  • Larval fish can consume 50 to 300% of their body weight per day.

  • Sub-adult fish require 2 to 10% of their body weight per day.

Consequences of Overfeeding Fish

• Overfeeding leads to uneaten feed, which can poison the environment.

• Decay of protein results in toxic substances like ammonia, nitrite, and nitrate generated by bacteria.

• This can impair immune system function and decrease dissolved oxygen levels in the water.

• A practical feeding rule is to only feed as much as the fish can consume within 15 minutes.

Types of Fish Foods

• Medicated Feeds: Approved by the FDA for specific treatment, such as against internal parasites. These are vital for quick intervention in sick fish that stop feeding.

  • Anti-parasitic Medications for both marine and freshwater fish.

  • Focus on non-toxic treatments that are easily removed from water.

Feeding Rate, Frequency, and Timing

• Factors that influence feeding rates and timing include:

  • Optimal growing temperatures.

  • Variety in fish species and size.

  • Seasonal changes and fluctuations in dissolved oxygen levels.

Labor and Operational Considerations

• Feeding frequency varies depending on:

  • Farm size:

  • Small farms often feed twice daily.

  • Larger farms may feed once a day due to labor constraints.

  • Small larval fish and fry require high protein diets and frequent feedings, often in excess.

Feed Types and Characteristics

• Fish should ideally be fed pelleted feed. Types include:

  • Extruded or pressure pelleted feeds.

  • The use of hard or floating pellets can affect feeding efficiency.

  • A good combination typically comprises 10 to 20% floating feed and 80 to 90% sinking feed.

Optimal Pellet Size

• Pellet sizes must ensure:

  • Too small pellets can lead to inefficient feeding.

  • Too large pellets risk choking the fish.

  • Ideal pellet size should not exceed 20% of the mouth opening.

Delivery Systems for Fish Feed

• Various feeding delivery systems include:

  • Hand-fed

  • Blower feeders

  • Demand feeders

  • Automatic and Demand Feeders save labor and time but involve additional expenses.

Insects as an Alternative in Fish Nutrition

Benefits of Insects in Fish Diets

• Insects offer:

  • A rich source of protein and energy.

  • Environmental and sustainability benefits.

  • Potential to replace fish meal and fish oils.

• Despite palatability and anti-nutritional challenges, insects are a viable alternative protein source.

Nutritional Composition of Insects

• Insects are rich in protein, lipids, and have low fiber content. They do not possess significant anti-nutritional factors, allowing for easier digestion and absorption by fish.

• They grow quickly and yield high feed conversion efficiency.

Comparison of Insect Meals to Traditional Fish Feeds

Chemical Composition of Insect Meals

Amino Acid Composition in Insect Meals

• 
  

• Data shows amino acid profiles of various insect meals compared to traditional feeds:
  

  Amino Acid	Black soldier fly	Housefly maggot	Mealworm	Fishmeal	Soymeal
  Methionine	2.1	2.2	1.5	3.5	2.7
  Leucine	7.9	5.4	8.6	7.5	5.8
  Challenges in Using Insects

  • Replacement rates of insect-based diets generally remain below 25 to 30%, due to variability in nutrient composition and nutritional value across species.

  Conclusion

  • The aquatic environment influences fish energy expenditure and nutrient needs when formulating diets. It is crucial to consider dietary habits and the morphology of the fish's gut structure across species and developmental stages.

  Questions?

  • Facilitated open discussion regarding learning and application of fish nutrition principles in aquaculture.