Do Fish in Aquaponics Systems Need Light?

February 10, 2025

The three key components of an aquaponics system: fish, plants, and beneficial bacteria, work together to create a natural balance. Fish produce waste, which beneficial bacteria convert into nutrients that plants can absorb. In return, the plants help purify the water, creating a healthy environment for the fish.

While it’s well known that plants need light for photosynthesis, many aquaponics enthusiasts wonder: Do fish in aquaponics systems need light? Since fish live in various natural habitats, from sunlit shallow waters to dark riverbeds, understanding their lighting needs is essential for maintaining their health and well-being.

This blog will explore whether fish require light in an aquaponics setup, how different lighting conditions impact their growth and behavior, and best practices for managing light exposure to maintain a thriving and balanced system.

Understanding Fish and Light in Aquaponics

Lighting plays a crucial role in aquaponics, but its necessity varies between plants and fish. While plants require light for photosynthesis, fish do not rely on light in the same way. However, light exposure can still affect their behavior, stress levels, and overall well-being. Understanding how fish interact with light, both in their natural habitats and in captivity helps aquaponics growers create a balanced and healthy system.

Do Fish Require Light for Survival?

Unlike plants, fish do not need light for survival, but their natural environments often provide some level of light exposure. The necessity of light depends on the fish species and their adaptation to different water conditions.

Natural Habitats of Common Aquaponics Fish

Different fish species used in aquaponics come from a variety of natural environments, each with different light conditions:

Tilapia: Native to warm, shallow waters where sunlight penetrates easily. They are accustomed to a natural day-night cycle.
Catfish:Typically found in murky rivers and deep waters with limited light. They rely more on touch and smell than vision.
Goldfish: Originating from ponds and slow-moving rivers with moderate light exposure. They are adaptable to various lighting conditions.
Trout:Preferring cold, clear streams and lakes, trout experience moderate to high natural light levels.

Do Fish Use Light for Essential Biological Functions?

Light influence fish behavior and biological rhythms. Some fish species use light to:

Regulate their circadian rhythm (internal biological clock).
Differentiate between daytime and nighttime for rest and activity cycles.
Recognize food and detect movement in their environment.

However, some fish, particularly those adapted to deep or turbid waters, can thrive in low-light conditions without any adverse effects.

The Differences Between Diurnal and Nocturnal Fish Species

Fish species can be classified based on their activity patterns:

Diurnal fish (active during the day): These fish, like tilapia and goldfish, benefit from a consistent light-dark cycle to maintain normal activity and feeding behavior.
Nocturnal fish (active at night):Catfish and some other bottom-dwelling species prefer dim or dark conditions and may experience stress under excessive lighting.

How Fish Respond to Light in Captivity

When fish are kept in an aquaponics system, their response to light exposure may differ from their natural behaviors. The duration and intensity of lighting can influence their well-being, and improper lighting conditions may lead to stress or health issues.

Behavioral Changes Based on Light Exposure

Fish exposed to consistent, moderate light tend to exhibit normal swimming and feeding behavior.
Sudden light changes such as turning lights on in a dark room can startle fish, and cause them to dart around the tank, which may lead to injury or stress.
Nocturnal species may become less active if exposed to bright light for extended periods.

Stress and Health Implications of Too Much or Too Little Light

Excessive light exposure can cause stress, making fish more susceptible to disease and reducing their overall lifespan. It can also lead to excessive algae growth, negatively impacting water quality.
Insufficient light (total darkness) may disrupt feeding patterns, especially for diurnal fish, leading to reduced growth rates.
An imbalanced light cycle can interfere with reproductive behaviors in some species, making it harder for them to spawn naturally.

Role of Light Cycles in Fish Metabolism and Feeding Behavior

A regular light-dark cycle helps regulate fish metabolism, keeping feeding and digestion patterns consistent.
Fish tend to associate light with feeding times. Sudden or irregular lighting changes can disrupt their appetite.
Maintaining a 12-hour light / 12-hour dark cycle (or a natural day-night schedule) can help ensure fish remain stress-free and active.

The Role of Light in an Aquaponics System

Light plays a crucial role in aquaponics, not only for plant growth, but it also affects fish health and the overall stability of the system. While fish do not require light for survival, their exposure to light can influence their behavior, stress levels, and metabolic functions. Additionally, light has a direct impact on water quality, particularly through its effect on algae growth. Understanding how to regulate light exposure in an aquaponics system helps maintain a balanced and healthy environment for both fish and plants.

The Impact of Light on Fish Health and Growth

Light exposure can influence fish health, growth rates, and overall well-being. While some fish are highly adaptable to different lighting conditions, others require a stable light-dark cycle to function optimally.

Does Light Exposure Affect Fish Growth Rates?

Moderate light exposure can support normal fish behavior, leading to consistent feeding habits and healthy growth.
Studies suggest that some fish, like tilapia, exhibit slightly better growth under regular light-dark cycles compared to continuous darkness or excessive lighting.
Overexposure to light can increase stress levels in fish, leading to a weakened immune system and lower growth rates.

How Prolonged Exposure or Darkness Impacts Fish Well-Being

1.Excessive Light:

Can cause stress, leading to erratic swimming, increased aggression, or reduced immune function.
May disrupt sleep cycles, preventing proper rest and recovery.
Can make fish more vulnerable to diseases due to prolonged stress.

2. Continuous Darkness:

May lead to decreased activity in diurnal species like tilapia and goldfish.
Can disrupt feeding habits, potentially reducing growth rates.
Could interfere with breeding and reproductive cycles in some species.

Recommendations for a Natural Light-Dark Cycle

To create an optimal lighting schedule for fish in an aquaponics system:

Mimic a natural day-night cycle: A 12-hour light / 12-hour dark cycle works well for most aquaponics fish.
Avoid sudden changes in light: Instead of abruptly turning lights on or off, use timers or dimmers to simulate sunrise and sunset transitions.
Provide shade or hiding spots: If using artificial lighting, include shaded areas or shelters where fish can retreat if they want less exposure.
Consider the fish species: Species like catfish thrive in lower light conditions and may benefit from dim lighting or indirect natural light.

The Relationship Between Light and Water Quality

Light doesn’t just affect fish, it also influences water conditions, particularly through its role in algae growth. Excessive light can lead to unwanted algae blooms, which may disrupt the balance of an aquaponics system.

1. How Light Influences Algae Growth in Aquaponics Tanks

Algae require light, water, and nutrients (such as nitrates and phosphates) to grow.
Overexposure to light, especially direct sunlight or strong artificial lights, can trigger rapid algae blooms.
Algae consume oxygen at night, which may reduce oxygen levels for fish, leading to stress or suffocation.
Excess algae can clog filtration systems, reducing water circulation and oxygenation.

2. Managing Excessive Algae Blooms to Maintain Water Quality

To prevent uncontrolled algae growth in aquaponics systems:

Limit direct sunlight exposure: If your tank is outdoors, use shade covers, floating plants, or UV-blocking materials to reduce excessive light.
Optimize artificial lighting placement:Avoid positioning lights directly over the fish tank. Instead, focus on lighting the plants while keeping fish in dimmer areas.
Monitor and control nutrient levels: Algae thrive on excess nutrients, so ensure the system is properly balanced by avoiding overfeeding fish and maintaining effective filtration.
Introduce algae-eating species: Some aquaponics setups incorporate algae-eating fish (e.g., plecos) or snails to help naturally control algae growth.

3. Does Artificial Lighting Contribute to Unwanted System Imbalances?

Too much artificial light can lead to overactive fish, excessive algae growth, and increased stress levels.
Incorrect lighting spectrum an promote algae growth more than others. Using full-spectrum LED or cool-colored fluorescent lights can reduce algae buildup.
Poorly timed lighting schedules – Keeping lights on for too long (beyond 12-14 hours per day) can lead to disruptions in fish behavior and encourage algae problems.

The Best Practices for Lighting in an Aquaponics System

Proper lighting management is essential for maintaining a well-balanced aquaponics system. While plants require adequate light for photosynthesis, fish have different needs. Overexposing fish to light can lead to stress, while keeping them in complete darkness may disrupt their natural behaviors.

Natural vs. Artificial Light for Aquaponics Fish

Understanding the advantages and limitations of natural and artificial light can help aquaponics enthusiasts create an optimal environment for their fish.

Benefits of Natural Sunlight for Aquaponics Systems

Energy-efficient and cost-effective:Sunlight is free and provides full-spectrum light, making it an excellent choice for outdoor systems.
Supports plant growth naturally:Sunlight ensures plants receive optimal wavelengths for photosynthesis without the need for artificial grow lights.
Regulates fish behavior: A natural day-night cycle helps fish maintain their circadian rhythm, reducing stress and promoting healthy feeding patterns.

When Artificial Lighting Is Necessary

Although natural light is ideal, artificial lighting is sometimes required, especially for indoor aquaponics systems or setups in areas with limited sunlight. Situations that require artificial lighting include:

Indoor aquaponics systems: Without access to sunlight, artificial lighting is necessary for plant growth and maintaining a consistent light cycle for fish.
Winter months or low-light regions: In locations with long winters or cloudy conditions, supplemental lighting ensures plants receive enough light while providing fish with a stable light-dark cycle.
Systems placed in shaded areas: If an outdoor system is in a location that receives limited sunlight, artificial lighting may be needed to balance light exposure.

Recommended Types of Artificial Lighting

Choosing the right type of artificial lighting can enhance system efficiency and minimize unwanted effects like excessive algae growth. The most suitable lighting options for aquaponics include:

LED Lights:Highly energy-efficient, long-lasting, and available in full-spectrum options. LEDs produce minimal heat, reducing the risk of overheating the water.
Fluorescent Lights:Provide good lighting for plant growth but are less efficient than LEDs. They work well for small indoor aquaponics setups.
Full-Spectrum Lights: Mimic natural sunlight, providing a balanced light source for both plants and fish. These are ideal for large-scale indoor systems.
Avoid Incandescent Bulbs: They generate too much heat, consume excess energy, and can disrupt the water temperature in an aquaponics system.

When using artificial lighting, it’s important to position the lights strategically to focus on plants while ensuring that fish receive indirect or diffused light rather than direct exposure.

Establishing a Proper Light Schedule for Fish

Just as humans thrive with regular sleep-wake cycles, fish also benefit from a consistent light-dark schedule that mimics their natural environment.

1. Ideal Day/Night Cycle for Fish Health

A 12-hour light / 12-hour dark cycle is generally recommended for most aquaponics fish species. This replicates a natural daylight cycle and ensures a healthy balance of activity and rest.
Some nocturnal fish (e.g., catfish) may prefer shorter light periods or dim lighting during the day to reduce stress.
Avoid exposing fish to 24-hour lighting, as it can disrupt their circadian rhythm, increase stress levels, and negatively impact immune function.

2. How to Regulate Light Exposure to Reduce Stress

Use timers for artificial lighting: This ensures a consistent light schedule and prevents sudden exposure to bright light.
Gradual light transitions: Sudden changes from darkness to bright light can startle fish. Using dimmers or placing indirect lighting in the tank helps reduce shock.
Provide shaded areas: Including rocks, driftwood, floating plants, or artificial shelters allows fish to retreat if they feel overstimulated by light.

3. Adjusting Light Duration for Different Fish Species

Different fish species have varying sensitivities to light:

Tilapia, goldfish, and trout:Thrive with 12-14 hours of light per day, mimicking natural daylight conditions.
Catfish and other nocturnal fish:Prefer 8-10 hours of dim light, as they are more active in low-light conditions.
Sensitive species: Some fish, such as koi, can become stressed under excessive artificial lighting, requiring softer or indirect lighting in the tank.

Common Myths and Misconceptions About Fish and Light

Some aquaponics enthusiasts believe that fish need constant light for energy, that they can’t see in the dark, or that lighting is necessary for breeding. However, these assumptions are not always accurate. Let's take a closer look at some of the most common myths about fish and light.

1. Do Fish Need Constant Light to Stay Active and Healthy?

One of the most widespread myths is that fish require continuous light exposure to remain active, eat properly, and grow efficiently. This is not true, just like humans and other animals, fish need a balanced light-dark cycle to regulate their biological processes.

Too much light can be harmful:Excessive exposure to artificial light or prolonged daylight hours can cause stress, disrupted feeding patterns, and a weakened immune system in fish.
Fish require periods of darkness: A natural light cycle (e.g., 12 hours of light and 12 hours of darkness) helps fish rest and maintain their circadian rhythm.
Constant light may lead to overstimulation: Some fish, especially nocturnal species like catfish, may become anxious or less active if exposed to too much light.

2. Can Fish See in the Dark?

Another common misconception is that fish cannot see in the dark and need light to navigate their environment. While their vision differs from humans, most fish are well-adapted to low-light or even dark conditions.

Fish have evolved to live in various light environments:Many species naturally inhabit murky waters, deep lakes, or shaded riverbeds where light is minimal.
Fish rely on other senses:Instead of depending solely on vision, fish use their lateral line system (a sensory organ that detects water movements and vibrations) to navigate in the dark.
Some fish have enhanced night vision:Certain species, such as catfish and trout, have special adaptations that allow them to see in dim or dark conditions.

3. Is Lighting Necessary for Fish to Breed in Aquaponics Systems?

While light can play a role in some fish breeding behaviors, it is not always a critical factor in aquaponics systems. The necessity of light for breeding depends on the species:

Some fish require specific light conditions for spawning:Certain species, like tilapia, may breed more effectively when exposed to consistent light cycles that mimic natural conditions.
Others rely on temperature, water quality, and environmental cues: Many fish species prioritize factors such as water temperature, pH balance, and nutrient levels over lighting when determining the right time to reproduce.
Overexposure to artificial light does not encourage breeding:While natural light cycles can influence reproductive behavior, prolonged or unnatural lighting conditions can actually disrupt spawning activities.

Conclusion

Lighting plays a crucial role in aquaponics, but its impact on fish differs from its importance for plants. While fish do not rely on light for survival, a well-regulated light-dark cycle helps maintain their health, behavior, and overall system balance. By mimicking natural lighting conditions, using the right artificial lights when necessary, and preventing common mistakes, you can create an optimal environment for both fish and plants in your aquaponics setup.

Are you currently using artificial lighting in your aquaponics system? Have you noticed any changes in fish behavior based on light exposure? Share your experiences in the comments below! Stay tuned for more expert tips on aquaponics care and system optimization!