Background: U.S. aquaculture sales reached $1.1 billion in 2005 – an increase of 11.7% since 1998 – and it is anticipated that this growth will continue.

Because aquaculture is a large-scale production industry, disease is always a concern.

Various chemicals are used to prevent disease outbreaks, including antibiotics.

Nitrification plays a major role in aquaculture – ammonia is toxic to fish at high levels, but always present as a metabolic by-product.

Discharge of nutrients, including nitrogen, one of the major environmental concerns regarding aquaculture effluents.

The Impacts of Chemotherapeutics on Nitrifying Bacteria in

Aquaculture Systems

G.D. Boardman – Civil & Env. Eng.

S.A. Smith – VMRCVM

N.G. Love – Civil & Env. Eng.

G.J. Flick – Food Science & Technology

Objectives:

1) To observe the impacts of common aquaculture chemotherapeutics on:

the water quality in an aquaculture system, specifically with respect to nitrification

the population density and metabolic activity of the nitrifying bacteria in the aquaculture system

2) To determine if the impacts can be proactively mitigated

Results: Preliminary results indicate that for antibiotic-medicated feeds, nitrification is inhibited during active dosing, but recovers quickly once dosing stops (see graph at left)

Fluorescent in-situ hybridization (FISH) results show that nitrifying bacteria are a very small population within the biofilms that are formed in aquaculture systems.

Amy K. Cheatham, P.E.

Civil and Environmental Engineering

418 Durham Hall

Blacksburg, VA 24060

Aquaria set-up for chemotherapeutic trials

Hypothesis: The nitrification process will be temporarily inhibited, but will recover quickly once treatments end

Inhibition observed will be with respect to metabolic activity of the bacteria rather than with respect to changes in the population composition or density

Methods:Aquaria (20-gallons each) are set up using standard box filters and oxygen supplies and housing tilapia; trials and controls all conducted in triplicate.

Chemotherapeutics are dosed in accordance with established guidelines.

Water quality is sampled before, during, and after the dosing periods to obtain a profile of the response and recovery of the system. Most water quality parameters are analyzed using HACH reagents and methods.

8-welled Teflon-coated microscope slides are suspended into the aquaria to collect samples of the biofilm formed within the system. Slides are fixed immediately upon collection and processed using fluorescent in-situ hybridization (FISH). FISH allows for the observation of shifts in the population composition and density of the nitrifying bacteria as a result of the chemotherapeutic exposure.

Samples collected from filter and analyzed using specific oxygen uptake rates (SOUR). SOUR allows for the observation of shifts in the activity of the nitrifying bacteria as a result of the chemotherapeutic exposure.

Number of samples is dependent on the dosing frequency of the chemotherapeutic being tested.

Once data are obtained regarding the response of the nitrification process, experiments will be conducted to determine if measures can be taken to proactively mitigate those impacts.

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

-3 -2 -1 1 2 3 4 5 6 8 12 15 20 23 28 30 34 37 42 45 47 50 54 57 61 63

Time (days)

Romet

Control

TA

N (m

g/L

)

Pre-dosing Post-DosingDosing

Total Ammonia-Nitrogen (TAN) response to Romet-30® exposure

FISH image of aquaculture biofilm; blue-green – ammonia-oxidizing bacteria, dark blue – other bacteria

Trials are currently being conducted using chelated copper and formalin

Future trials will be conducted using Chloramine-T and potassium permanganate

Acknowledgements:

A special thanks to the U.S. Department of Agriculture and Blue Ridge Aquaculture (Martinsville, VA).