The world’s human population is growing rapidly, and increasing food resources are required to sustain this population. Fish can provide protein-rich food for humans, and the demand for fish for human consumption is increasing. Over half of fish in the human diet are now grown via aquaculture, and aquaculture largely relies on fishmeal as a food source for the fish being grown. Fishmeal is made from fish, and because fishmeal has recently declined in supply and increased in cost, it is limiting the further growth of aquaculture. Therefore, there is a critical unmet need for new sources of protein to feed aquaculture fish. Insects can help fill this need.

Insects are attractive as sources of fish feed because they are abundant, rich in protein and lipids, and cost effective. To evaluate insects for fish feed, Tauqeer Hussain, Hafiz Muhammad Tahir, Ph.D., and colleagues at the Government College University and the University of Education in Lahore, Pakistan, tested if feeding meal containing pupae of silkworms (Bombyx mori) to Nile tilapia (Oreochromis niloticus) affected the fish’s growth, health, survival, or blood health. Their findings were reported in March in the Journal of Economic Entomology.

Silkworm pupae are a byproduct of the silk production process. “Silkworm larvae spin cocoons and then pupate inside these cocoons containing silk fibers,” the authors write. “Later, the silk is obtained by placing the cocoons in hot water to unwind the silk fibers, leaving dead pupae as waste material.” For every one kilogram (kg) of silk made, 1.5–2 kg of pupae waste is made. Globally, about 90,000 metric tons of silk is produced each year, which translates to a global production of silkworm pupae of nearly 200,000 metric tons per year. And silkworm pupae are not only abundant; they are ideal for fish food because they are 50–70% animal protein.

Earlier studies found improved growth in several fish species with the use of silkworm pupae meal. The investigators in the present study examined the effects of silkworm pupae meal on genetically improved farmed tilapia (GIFT), a genetically enhanced strain of Nile tilapia (Oreochromis niloticus) popular in aquaculture. They tested if consuming silkworm pupae meal affected growth and survival of GIFT tilapia, including weight gain, percentage weight gain, survival rate, average daily growth, feed conversion ratio, and feed efficiency ratio.

For the study, the investigators obtained fingerling fish from a fish hatchery and acclimated them to a 1,000-liter tank for two weeks. During the acclimation period, the fish were fed a fishmeal diet once per day. During the experimental period, the fish were fed twice per day.

The study used a design of one control group and three treatment groups. The control group received food consisting of fishmeal, soy bean meal, maize gluten, and other ingredients. In the three treatment groups, fish received food in which the fishmeal had been replaced with 10%, 20%, or 40% ground silkworm pupae.

Hussain, Tahir, and colleagues found that the fish receiving silkworm pupae meal showed significantly higher weight gain, significantly higher average daily growth, and a significantly higher feed-efficiency ratio than fish in the control group. Similar studies have also found an increase in growth with the use of silkworm pupae meal in common carp (Labeo rohita), largemouth bass (Micropterus salmoides), and African catfish (Clarias gariepinus).

The investigators in the present study found no significant difference in survival rate or feed-conversion ratio between the fish fed silkworm pupae meal and the control fish. This agrees with previous studies that found that silkworm pupae in fish feeds did not affect survival in mirror carp (Cyprinus carpio), GIFT tilapia (Oreochromis niloticus), and juvenile mirror carp (Cyprinus carpio).

The investigators also tested if silkworm pupae affected the condition of the fish’s blood. They found that hemoglobin level, red blood cell count, white blood cell count, and hematocrit were all significantly higher in fish receiving the silkworm meal than in control fish receiving fishmeal. Mean corpuscular volume was significantly higher in the 20% silkworm pupae treatment and the 40% silkworm pupae treatment than in the control. Mean corpuscular hemoglobin and mean corpuscular hemoglobin concentration were not significantly different between any treatment groups and the control. “The improvement in all examined hematological indicators following the addition of silkworm pupae to fish feeds suggests that fish’s immune system and overall health, particularly their cardiovascular health, have improved,” the authors write.

The researchers concluded that “insect proteins such as silkworm pupae have been proved to be a promising and sustainable alternative to fishmeal because of their availability, cost effectiveness and rich nutritional value.” The use of insects such as silkworm pupae as food for fish can provide an abundant protein source at an affordable price; they could also provide additional benefits. For example, disease in fish is a major problem in aquaculture, often leading to large economic losses. Because—as the blood components of this study showed—silkworm pupae meal can improve the health of farmed fish, it could help alleviate this disease problem. Similarly, because antibiotic resistance can arise in farmed fish populations, silkworm pupae meal’s positive effect on fish health may be able to reduce the need for antibiotics in aquaculture.

Further research on silkworm pupae feed could continue to test the feed in a variety of farmed fish species and test the feed over a range of percentages to fine tune formulations. As aquaculture continues to grow rapidly, this protein-rich meal for fish promises to play a valuable role in expanding high-quality protein sources for people around the globe.

Source - https://entomologytoday.org