Over the last centuries, we have greatly depleted the oceans, which used to have superabundance. Most unrecognized, this has dramatically reduced their resilience and their ability to mitigate challenges such as pollution and extreme climate. The decrease in fish in rivers and oceans destabilizes and puts under threat the global food web. Aquaculture (the farming of fish) has been posed as a solution. However, aquaculture fish are typically fed with processed fish caught in the wild. There is a need to find alternatives.
Here, we present a plant-based fish diet that is available at little to no cost, requires very little labor and can be grown in immediate proximity to the fish. In the last several months, our team has experimented with this diet and gradually reduced the commercially purchased fish feed for our Nile Tilapia fish. 70% of our fish diet now consists of a mix of chaya mansa (tree spinach), colocasia leaves, moringa leaves and banana leaves, with the commercial feed now at 30% and decreasing.
The advantages of transitioning from a commercial fish feed to a locally-grown organic fish feed are several. It reduces the costs, waste and energy required for transportation, processing, packaging and distribution. It assures that no artificial chemical compounds that might be used during commercial feed processing and conservation end up in the food chain, potentially compromising fish or human health. It adds to the overall nutritional value of fish feed, with micro and macronutrients which would be more bioavailable and better absorbed than commercial fish feed.
The factory produced fish feed is expensive and consists mostly of wild-caught fish. Several government-funded researchers and fish food manufacturers have been working on figuring out a recipe for fishless fish food. A current priority in the aquaculture industry is the need to partially or totally replace fishmeal with less expensive and easily available plant protein sources to reduce dependence on fish meal and soybean meal as the fundamental protein sources for aquatic animal diets without reducing the nutritional quality of feeds (Toan and Preston, 2010; Castillo and Gatlin, 2015).
We began studying the feasibility of using on-farm inputs as fish food as opposed to commercially processed fish feed pellets at The Venus Project Integrated Aquaponics System. Experiments are being conducted to evaluate the effect of using on-farm inputs, especially chaya mansa leaves, as a partial substitute of fish meal in fish diet on growth performance and feed utilization of Nile tilapia (Oreochromis niloticus) fish. The fish were initially fed with a diet of Growell company with a minimum analysis of 32% crude protein, 3.5% crude fat, and not more than 7.0% crude fiber. Our daily feed regimen for fish now includes 30% weight of the above-mentioned diet plus on-farm inputs such as colocasia leaves, moringa leaves, banana leaves and chaya mansa leaves. These on-farm resources are cheap to produce, locally available, and are self-sustaining. We were able to cut down the pelleted fish feed to over 70% with this experiment. Results have begun to demonstrate that growth performance parameters (final body weight, weight gain, specific growth rate, and survival rate) were not affected at all with increasing the above on-farm inputs in fish diet.
Moringa (Moringa oleifera) or popularly called drumstick tree is traditionally cultivated as a backyard plant and used as a vegetable. It can also be grown as part of a living fence. Parts of Moringa used traditionally as human food are green pods, tender leaves, flowers, and oil from seeds. (Gopalakrishnan et al., 2016)
Colocasia esculenta is cultivated for its large, starchy, spherical corms (underground stems), commonly known as “taro root,” which are consumed as a cooked vegetable, made into puddings and breads. The large leaves of the taro are commonly stewed. (Buntha et al., 2008; F. Attalla et al., 2021)
Chaya Mansa (Cnidoscolus aconitifolius) leaves “are an excellent source of a number of essential nutrients for a healthy, balanced diet. In fact, Chaya is more nutritious than many green leafy vegetables such as spinach, Chinese cabbage and amaranth. The leaves are very high in protein, calcium, iron and vitamins A and C.” (USAID Technical Bulletin #92, 2013)
Other terrestrial plant leaf meals: Use of other leaf meals from terrestrial plants such as banana, cowpea, squash, broad bean, papaya beans, and cucumber are being evaluated for use as a potential protein source in the diet of Nile tilapia fish to replace fish meal. (Dorothy et al., 2018)
Ongoing Research & Development
We are constantly looking for ways to further improve upon what we are doing. A good improvement reduces costs and work, enhances nutrition and yield, increases the resiliency and diversity of the system, creates mutually-beneficial relationships, has positive ecological and health effects, and enables new possibilities. Here are some of the current improvements we are engaged with, at various stages of development:
1. Growing Mushrooms
Mushrooms can be added to the system without requiring any additional space, by utilizing the shaded and unused ground areas beneath the vegetables. The moisture, temperature, and nutrient-rich aquaculture water we have seem like very favorable conditions for mushroom growth. We have done two trials so far, which were unsuccessful due to harsh climate and the different growing medium (sand). Learning from our experiences, we are getting ready to do a third trial.
2. Growing Berries
Similar to the above, there is a shaded area between the ground and the level of the vegetables. Berries that like shade can be grown in this space. We are currently researching which berries might be suitable to grow here, such as strawberries under the tomatoes.
3. Silk Clothes
Would it be cool if in addition to fruits and veggies, we could also grow our clothes? We are looking at possibilities for introducing silkworms into our system. They eat certain kinds of leaves, such as mulberry leaves, and secrete the silk thread out of which silk clothes are made. We are looking to obtain mulberry saplings from a nearby farmer who is an expert in sericulture.
4. Extending Produce Shelf Life
It often happens that a large quantity of produce is ready for harvesting, but there is not enough need for this much food right away. This leads to the produce deteriorating. It would help if there was a sort of a buffer, so that the produce is steadily available as the need for food arises. One way this could be done is by keeping the produce at a lower temperature. We are looking into natural cooling systems which use the evaporation of water to achieve a cooling effect. Two examples are clay pot coolers and charcoal cooling chambers.
5. Reducing Or Removing External Fish Feed
The biggest ongoing cost in an aquaponics setup like ours is the commercial fish feed which is purchased from outside vendors. It is an external input that often involves harmful health and ecological practices in its making. It also relies on a supply chain with its own transportation and infrastructure. With the above update, we are happy to report a 70% reduction in the use of commercial fish feed.
If you are interested in any of the above or other possibilities, we invite you to contact our team. Suggestions and feedback are also welcome in the comments below.