Revista de Pesca e Aquicultura
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Measuring Body Size in Small Marine Fishes: A Comparison of Three Non-intrusive Methods

Stanton G Belford, Nanette E Chadwick, Maroof A Khalaf

Studies of non-intrusive techniques are important in fisheries biology, because research methods may inadvertently cause damage to the study organisms. In addition, current effects of human–environment interactions coupled with future trends in global climate change likely will lead to increased monitoring of fish population dynamics. The aim of this study is to analyze the effectiveness of three simple non-intrusive techniques to accurately obtain body length measurements of anemonefish and other small fishes. Frequently used catch and re-capture methods are stressful to fishes, and can alter their behaviors upon release, thus negatively impacting field ecological studies. Alternate methods to non-intrusive sizing of reef fishes are needed, and these methods should be compared to determine the most effective and efficient means of collecting the targeted data. Three non-intrusive techniques were employed to obtain accurate fork length (FL) measurements of the two-band anemonefish, Amphiprion bicinctus. Comparison of these methods revealed that fish lengths from visual estimates by self-contained under water breathing apparatus (SCUBA) divers did not differ significantly from those estimated using both video-mirror and Tps-mirror techniques (ANOVA, F(2,60) 5 1.572; p 5 0.22). Under laboratory conditions, fish sizes from manual measurements also did not differ significantly from those obtained using either mirror method (ANOVA, F(2,81) 5 0.489; p 5 0.61), demonstrating that the mirror techniques accurately assess fish size under both laboratory and field conditions. These methods were not effective in identifying or tracking individual fish among years in the field, due to high rates of fish mobility and turnover. However, they were useful in determining short-term anemonefish migration among sea anemone host.