Cleaner shrimp are a sustainable option to treat parasitic disease in farmed fish

Abstract

Chemical use is widespread in aquaculture to treat parasitic diseases in farmed fish. Cleaner fish biocontrols are increasingly used in fish farming as an alternative to medicines. However, cleaner fish are susceptible to some of their clients' parasites and their supply is largely dependent on wild harvest. In comparison, cleaner shrimp are not susceptible to fish ectoparasites and they can be reliably bred in captivity. The effectiveness of shrimp in reducing parasites on farmed fish remained unexplored until now. We tested four cleaner shrimp species for their ability to reduce three harmful parasites (a monogenean fluke, a ciliate protozoan, and a leech) on a farmed grouper. All shrimp reduced parasites on fish and most reduced the free-living early-life environmental stages - a function not provided by cleaner fish. Cleaner shrimp are sustainable biocontrol candidates against parasites of farmed fish, with the peppermint cleaner shrimp reducing parasites by up to 98%.

Figure 1

Effect of cleaner shrimp on Cryptocaryon irritans. (a) Reduction of C. irritans trophonts (parasitic stage) on fish by cleaner shrimp diurnally. (b) Nocturnally. (c) Reduction of C. irritans tomonts (environmental stage) diurnally. (d) Nocturnally. Data expressed as the proportion recovered.

Figure 2

Effect of cleaner shrimp on Neobenedenia girellae. (a) Reduction of sub-adult N. girellae (parasitic stage) on fish by cleaner shrimp diurnally. (b) Nocturnally. (c) Reduction of N. girellae eggs (environmental stage) diurnally. (d) Nocturnally. Data expressed as the proportion recovered.

Figure 3

Effect of cleaner shrimp on Zeylanicobdella arugamensis. (a) Reduction of sub-adult Z. arugamensis (parasitic stage) by cleaner shrimp diurnally or nocturnally. (b) Reduction of Z. arugamensis cocoons (environmental stage) by Lysmata vittata over 24 hours. Data expressed as the proportion recovered.

Figure 4

Shrimp species performance matrix. Ranking: Undetermined, no current data; Insignificant, p > 0.05; Poor, 11–24% reduction; Moderate, 25–49% reduction; Good, 50–74% reduction; Excellent, 75–100% reduction.

Figure 5

Experimental design demonstrating treatment and control setup for a single replicate for parasitic (on fish) and environmental stages, and shrimp species used. (a) Neobenedenia girellae. (b) Cryptocaryon irritans trophont. (c) Zeylanicobdella arugamensis. (d) Cryptocaryon irritans tomonts (cysts) or Z. arugamensis cocoons on microscope slide. (e) Embryonated Neobenedenia girellae eggs attached to bridal tulle. LS. Recirculating seawater life-support system with filtered influent (blue arrows), and effluent (grey arrows) schematic water flow; 1. Fitted tank lid; 2. 60 µm mesh tank cover; 3. Individual experimental tank positioned inside a water catchment tray.