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Can Juvenile Crayfish Combat Schistosomiasis?

CSEF · 2017 Zoology Honorable_mention Award

Austin D. Roberts · La Colina Junior High School, Santa Barbara, Santa Barbara County

Overview

Objectives/Goals QUESTION: Can juvenile crayfish, Procambarus clarkii, control population levels of the snail Biomphalaria glabrata? PURPOSE: This experiment tested the ability of juvenile crayfish to control populations of intermediate host snails that can transmit schistosomiasis to humans. HYPOTHESIS: My hypothesis was that juvenile crayfish could control population levels of Biomphalaria glabrata snails,reduce egg masses and 0-2mm hatchlings in aquaria over 30 days. Methods/Materials Experiments had three control 1 gallon aquaria with 5 snails (2-8mm, 2-12mm and 1-15-20mm diameter snail), red leaf lettuce, 0.2 grams of calcium carbonate powder, and airstones. Size-specific Predation Ability: The maximum size of Biomphalaria glabrata snails consumed by different sizes of Procambarus clarkii crayfish was determined. One crayfish was introduced into each treatment aquarium with snails. Aquaria were checked daily for consumption of B. glabrata snails. Effect of Crayfish Predation on a snail population: Three 12mm carapace length (CL) crayfish were used in the population experiment. The experiment ran 30 days and snail, egg mass and hatchling (0-2mm diameter) consumption was determined. Results In the size-specific experiment, crayfish 14mm CL and larger killed the largest snails offered (15-20mm diameter). The maximum size class of snail consumed by 13mm CL crayfish varied from 12mm to 15-20mm in size. No snails died in control aquaria over the same time period. In 30 day population experiments, 12mm CL crayfish significantly reduced snail populations (8-20mm diameter) to 2 compared to 4.3 in control aquaria with no crayfish. Egg masses were reduced to 7.3 compared to 41.3 in control aquaria and hatchlings were reduced to 0 compared to 10 in control aquaria. Conclusions/Discussion Very small juvenile crayfish effectively reduced population levels of B. glabrata snails, consumed egg masses and totally blocked recruitment of 0-2mm hatchling snails into the snail population. The ability of very small crayfish to control population levels of B. glabrata snails is a very promising step in our knowledge of the size of crayfish that can be effective in controlling B. glabrata population sizes. In other field studies, fewer intermediate host B. glabrata snails has translated into reduced schistosomiasis transmission to humans.

Summary statement

My science project showed that juvenile crayfish could control a laboratory population of snails that transmit human schistosomiasis, a parasitic worm disease that infects 200 million people worldwide and kills 300,000 people annually.

Help received

I discussed the experimental design with Dr. Kuris and developed how to conduct the experiment. I asked what statistical tests to run and then I went online to study statistical tests and run them in Excel.

Awards (1)

  • Honorable Mention

Competition history

  • CSEF 2017 Zoology · Entry J2317

Resources

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