Fish feed is one of the highest ongoing costs in aquaponics, and for many growers, it’s also one of the biggest points of frustration. Commercial pellets can be expensive, hard to source consistently, and often rely on fishmeal that is not environmentally sustainable. That’s why more aquaponics growers are asking an important question: Are there effective alternative fish foods that actually work in aquaponics systems?
The short answer is yes, when done correctly.
Alternative fish food in aquaponics can lower operating costs, improve sustainability, and even help you become more self-reliant. Options like duckweed, black soldier fly larvae, and DIY feed blends have been tested by growers and researchers alike. But there’s an important catch: feeding fish the wrong way, or switching too fast, can harm fish health, destabilize water quality, and stress your entire system.
That’s where this blog comes in.
In this blog, you’ll learn:
- What alternative fish foods work best in aquaponics
- How each option affects fish growth and system health
- Which alternatives are safest for beginners
- How to test new feeds without risking a system crash
By the end of this guide, you’ll understand which alternative fish foods make sense for your system, and how to use them with confidence.
The Best Alternative Fish Foods in Aquaponics
Before diving deep into each option, it helps to see the most common and proven alternative fish foods used in aquaponics side by side. Not all alternatives work the same way, and some are better suited for beginners than others. The key is choosing feeds that are nutritionally adequate, safe for your system, and easy to manage.
Below are the top fish food alternatives in aquaponics systems used by small-scale and home aquaponics growers.
1. Duckweed as an Alternative Fish Food in Aquaponics
Duckweed is one of the most talked-about alternative fish foods in aquaponics, and for good reason. It grows fast, thrives on nutrient-rich water, and can be cultivated directly within or alongside your aquaponics system. When used correctly, duckweed can significantly reduce feed costs while supporting healthy fish growth.
Why Duckweed Works in Aquaponics
Duckweed (Lemna and Wolffia species) is a small floating aquatic plant with a surprisingly strong nutritional profile. Under favorable conditions, duckweed can contain 30–40% protein, along with essential amino acids, vitamins, and minerals. This makes it especially suitable for omnivorous fish like tilapia, carp, and catfish.
- High in protein and fast-growing
- Easy to grow using system nutrients
- Needs proper harvesting and portion control
- Excellent partial replacement for pellets
For aquaponics growers, duckweed has two major advantages:
- It uses excess nutrients already in the system, helping recycle nitrogen and phosphorus.
- It can be grown continuously, reducing dependence on purchased feed.
This creates a more circular, resilient system which many growers are aiming for.
How to Grow Duckweed Safely
Duckweed prefers calm water, moderate sunlight, and nutrient-rich conditions. Many growers raise it in:
- A separate shallow tank or tote connected to the system
- A dedicated side loop to prevent overgrowth in the main fish tank
Key growing tips:
- Ideal pH range: 6.5–7.5
- Harvest frequently to prevent dense mats (which can reduce oxygen levels)
- Rinse before feeding if grown outside the main system
Overcrowding is the most common mistake. Thick duckweed mats can block light and reduce dissolved oxygen if left unmanaged.
How to Feed Duckweed to Fish
Duckweed can be fed:
- Fresh (rinsed and chopped for smaller fish)
- Dried and crumbled for easier storage and portion control
For beginners, it’s best to start small:
- Replace 10–20% of commercial pellets with duckweed
- Observe fish behavior, appetite, and water quality for 7–10 days
- Gradually increase only if results remain stable
Duckweed should supplement, not completely replace, a balanced commercial feed—especially in growing or breeding fish.
Common Mistakes to Avoid
- Feeding too much, too fast
- Letting uneaten duckweed decompose in the tank
- Assuming all duckweed species have identical nutrition
- Skipping water testing during feed changes
2. Black Soldier Fly Larvae as an Alternative Fish Food
If duckweed is the easiest plant-based alternative, black soldier fly (BSF) larvae are one of the most powerful animal-based options in aquaponics. They’re rich in protein and fats, highly palatable to fish, and well-studied as a replacement for traditional fishmeal when used properly.
Why Black Soldier Fly Larvae Are So Effective
BSF larvae contain:
- 40–45% protein (depending on diet and processing)
- Beneficial fats and micronutrients
- A natural texture and smell that fish readily accept
- High-quality protein and beneficial fats
- Strong fish growth when used correctly
This makes BSF especially useful for boosting growth rates when replacing part of a commercial pellet diet. Many studies and on-farm trials show strong results when BSF meal replaces 25–50% of fishmeal in formulated feeds without harming growth or feed conversion—particularly in tilapia and catfish systems.
How BSF Fit Into Aquaponics Systems
Black soldier fly larvae are typically:
- Grown in a separate bin using food scraps or agricultural waste
- Harvested and dried or frozen before feeding
- Ground into meal or mixed with other alternative feeds
Other Alternative Fish Food Options (And When to Use Them)
Duckweed and black soldier fly larvae are two of the strongest alternative fish foods for aquaponics, but they aren’t the only options available. Many growers experiment with additional alternatives to reduce costs, diversify nutrition, or make use of local resources. The key is understanding where these options fit, and where they don’t.
1. Plant-Based Commercial Feeds (Soy, Pea, Algae-Based)
Plant-based commercial feeds are often marketed as “sustainable fish feed.” They’re convenient, shelf-stable, and consistent in quality.
When they work well:
- As a partial replacement for traditional pellets
- For omnivorous fish like tilapia and carp
- When blended with insect or plant protein sources
Limitations to be aware of:
- Some lack essential amino acids (like methionine)
- Overuse can reduce growth rates if not balanced
- Anti-nutritional factors may affect digestion
Best practice: Use these feeds as one part of a blended diet, not as the sole food source.
2. DIY Feed Blends (Duckweed + Insects + Plant Meals)
DIY feed blends give growers the most control, and the most responsibility.
Common blends include:
- Dried duckweed + BSF meal
- Plant meals + insect protein
- Seasonal feeds adjusted by growth stage
Pros:
- Can significantly reduce feed costs
- Encourages local, circular systems
- Highly customizable
Cons:
- Requires testing and record-keeping
- Inconsistent mixtures without careful measuring
DIY feeds are best suited for growers willing to track fish growth and water parameters closely.
3. Kitchen and Garden Scraps (With Strong Caution)
Scraps are often mentioned as “free fish food,” but they come with the highest risk.
Safe use guidelines:
- Never feed raw meat, oils, or processed foods
- Compost, ferment, or convert scraps into insect feed first
- Use scraps indirectly (to grow BSF larvae or worms)
Direct feeding of scraps into fish tanks is not recommended for aquaponics systems.
Important Takeaway
No alternative fish food should replace pellets all at once. Successful growers almost always use partial replacement strategies, slowly introducing alternatives while monitoring fish behavior and water quality.
How Alternative Fish Food Affects Water Quality and System Health
In aquaponics, fish food is the engine that drives the entire system. Every bite your fish eat eventually impacts water chemistry, beneficial bacteria, and plant growth. This is why switching to alternative fish food without understanding system dynamics is one of the fastest ways to create problems.
The Feed → Fish → Bacteria → Plant Chain
Here’s the simplified flow:
- Fish consume feed
- Fish excrete waste (ammonia)
- Beneficial bacteria convert ammonia → nitrite → nitrate
Plants absorb nutrients to grow
When you change feed type, you change:
- The rate and composition of fish waste
- The speed of mineralization
- How nutrients become available to plants
Common Water Quality Changes to Watch For
When introducing alternative fish food, growers often see:
- Ammonia or nitrite spikes if digestion efficiency drops
- Increased solids from fibrous plant material
- Changes in pH due to altered biological activity
- Oxygen demand increases, especially with uneaten feed
These changes don’t mean alternative feeds are “bad” they simply mean the system needs time to adjust.
How to Protect Your System During Feed Changes
To keep your aquaponics system stable:
- Make feed changes gradually, over 1–3 weeks
- Increase monitoring (daily at first)
- Remove uneaten feed promptly
- Reduce feed amounts if fish behavior changes
Warning signs to act on immediately:
- Fish gasping at the surface
- Uneaten feed accumulating
- Cloudy water or foul smells
If any of these appear, scale back feeding and test your water immediately.
How to Test Alternative Fish Food Safely in Your Aquaponics System
Experimenting with alternative fish feeds can feel intimidating, but a structured, step-by-step approach ensures safety for both your fish and your system. Below breaks down a practical method used by successful aquaponics growers.
Step 1: Start Small
- Begin with one tank or a small portion of your fish rather than the entire system.
- Gradually introduce the alternative feed, keeping the rest of the diet as the original commercial pellets.
- Start with 5–10% of total feed as the alternative, then slowly increase.
Step 2: Monitor Water Quality Closely
- Check ammonia, nitrite, nitrate, pH, and dissolved oxygen at least daily during the first week.
- Observe for unusual signs like fish gasping, uneaten feed, or cloudiness.
- Make adjustments immediately if parameters drift outside safe ranges.
Tip: Keep a simple logbook or spreadsheet to track readings and feed ratios, it will save headaches later.
Step 3: Track Fish Health and Growth
- Weigh a small sample of fish weekly to monitor growth trends.
- Observe behavior, appetite, and overall vitality.
- Healthy fish should continue growing and actively feed without stress.
Step 4: Adjust Gradually
- Increase the alternative feed slowly, typically no more than 5–10% per week.
- Reduce or pause the new feed if you notice negative impacts on water quality or fish behavior.
- Maintain consistent portion sizes for accurate comparisons.
Step 5: Analyze and Decide
- Compare fish growth, water quality, and feed cost savings.
- Decide if the alternative feed can become a regular part of your system.
- Consider blending multiple alternatives for better nutrient balance.
Conclusion
Exploring alternative fish foods in aquaponics, like duckweed, black soldier fly larvae, plant-based feeds, and DIY fish food can help you save money, improve sustainability, and experiment safely in your system. The key is to introduce new feeds gradually, monitor water quality, and observe fish behavior. By blending options and testing carefully, you can maintain healthy fish growth while reducing reliance on commercial pellets.
Ready to take your aquaponics system to the next level?
This 5-hour Aquaponics Masterclasswalks you step-by-step through growing, preparing, and testing alternative fish feeds. With this course, you’ll learn exactly how to implement these strategies safely and confidently.
This course is the perfect next step for growers who want to turn theory into practice, reduce feed costs, and optimize their aquaponics system.
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