Effect of Black Fly Larva Diet Supplement on Goldfish (Carassius auratus) Reproduction in an Aquaponics System

Abstract

Aquaponics has become a major focus of aquaculture and related research in recent years. Advancements have been made in increasing production efficiency, however, research has focused on reared fish over ornamental fish, despite an estimated worth of over $1 billion per year in this industry. Our model organism, goldfish (Carassius auratus), are ornamental fish and closely related to koi, another valuable ornamental fish. Additionally, goldfish are often used as a model species in laboratory environments. They are resistant to variations in temperature, water quality, diet, and are tolerant of handling and experimental stress. A common problem in stressful environments, including aquaponics systems, is to supply a diet adequate for reproduction. Black Soldier Fly larvae (BSF) are often used as feed in aquaponics systems because of their nutritional content and the fish preference over pellet food. In previous studies, BSF has been shown to increase the total spawned eggs in Zebrafish (Danio rerio) when 25% of their diet was replaced with BSF. However, there was a significant decrease in the total spawned eggs when 50% of their diet was replaced with BSF supplement. In order to maximize viable spawned eggs and minimize the BSF supplement, we want to hone in on the ideal percentage of BSF meal in the diet of goldfish. We hypothesize that goldfish fed BSF meal will have more total spawned eggs than goldfish fed the control diet of pellet food. Additionally, we hypothesize that goldfish fed 20% BSF meal will have more total spawned eggs than the 40% BSF meal replacement. To test our hypothesis, 40 reproductive fish will be placed into four identical aquaponics systems (300 L/ tank, 10 fish /tank) that we assembled and tested at Texas State University (TXST). We already developed the culture of BSF and spawning goldfish techniques at TXST. The first and second tanks will act as controls being fed a pellet diet. The latter two tanks each will have an experimental diet of 20% BSF meal or 40% BSF. Additionally, each tank will be attached to a separate lettuce grow bed. The mating behavior and sex hormone/pheromone water release in tanks three and four will be compared to the control tanks and will determine what impact their diet has on mating. We will be collecting the eggs and counting how many eggs were laid in each treatment and counting the total spawned eggs. Additionally, any impacts on the growth of the lettuce will be determined. Aquaponics is a growing industry and increasing the efficiency of fish and crop growth while minimizing expense is paramount. Fish physiological studies in aquaponics will allow developing optimal fish rearing techniques necessary for the advance of the industry.