Electricity in Fish Research and Management
The book concentrates on Electric Fishing (or Electrofishing); an internationally accepted and widely used procedure for sampling fish. Over the past 50 years electric fishing has become a standard method for fishery studies and management e.g. establishing population densities and abundance. However, due to the potential hazards of the method (both to operators and fish) there is a continuing need to develop and promote best practice guidelines.
The author has studied fish ecology for 40 years and understands the need for information that reaches out to all levels of understanding in the field. Previous books on this subject have either been collections of scientific papers and/or technical reports or very simple instruction manuals. In this book theory and practice is explained using non-technical language and simple equations. It brings depth as well as breadth in both information and principles behind the methods and should be an invaluable tool to both fisheries managers and researchers.
Although the book is aimed at undergraduates, the clear explanation of the factors means that the book is suitable for all levels of practitioners.
Electricity in Fish Research and Management
Electric fishing (or electrofishing ) is the term given to a number of very different sampling methods. All have in common the utilisation of the reaction of fish to electrical fields in water for facilitating capture (Hartley 1980a, Pusey et al . 1998). At its most basic, electric fishing can be described as 'the application of an electric field into water in order to incapacitate fish, thus rendering them easier to catch'.
Despite over 100 years of study, the exact nature by which these effects are caused is still a matter of some debate (Sharber & Black 1999, cf. Kolz 1989, Reynolds et al . 1988, Snyder 2003). The basic principle is that the electrical field stimulates a muscular reaction (either involving the central and/or autonomic nervous system or not) resulting in the characteristic behaviour and immobilisation of the fish.
Two views on the underlying cause of the effect predominate, the 'Biarritz Paradigm' and the 'Bozeman Paradigm'. The former, which was proposed by Lamarque (1967, 1990) but also includes the principles underlying Kolz's Power Transfer Theory (Kolz 1989), considers the phenomenon to be a reaction to electrostimulation of both the central nervous system (CNS) and autonomic nervous system and the direct response of the muscles of the fish (i.e. a reflex response) (Sharber & Black 1999). In 1999, Sharber and Black (1999) proposed an alternative theory, the Bozeman Paradigm. In this theory the fish response is basically that of electrically induced epilepsy, and when the electrical stimulation overwhelms the CNS the (epileptic) seizures occur.
Little external research has been carried out on Sharber and Black's epilepsy theory, but many studies have either supported or refuted the theory regarding the role of the fish's nervous system in determining the effect. Haskell et al . (1954) considered that the effect was independent of the CNS, as freshly killed fish that had had their spines removed or been pithed still reacted to an electric field and 'swam' towards the anode. Flux (1967) also found that dead fish responded to an alternating current (AC) voltage gradient and attributed this to Vibert's (1963) assertion that, for a direct current (DC) waveform, in tetanus (where the fish's muscles go into spasm and are in a cramped state) the electricity is acting directly on the fish muscles (i.e. no CNS reaction). Sternin et al . (1976), quoting work by Danyulite and Malyukina (1967), also considered that their work disproved the role of neural action in stimulating the fish muscles and proved that electrotaxis is possible without participation of the brain. However, Stewart (1990), working on marine fish species, observed that a pulsed DC (pDC) waveform acted directly on the fish muscles, with the fish muscle reacting to each pulse, and considered that the electrical waveform was working in parallel with the nervous system to activate the fish's muscle system.
Given the wide variety of research findings on the fundamental cause of the effect, for the time being we need to accept that the underlying principles behind the response are not proven.
It is generally accepted by all researchers that it is the current density (amps/cm2), which can also be expressed as the power density (watts/cm3), which is the principle determinant of the behavioural response. The magnitude of the current density that the fish experience is governed by the applied voltage (and thus the voltage gradient (E) in the water), the conductivity of the water and the electrical conductivity of the fish.
In addition, it is possible that the fish skin acts in a way whereby electricity is more easily transmitted into the fish when there is a change in voltage potential around the fish: it is thought that this is due to the fish skin acting as a capacitor. This can be seen in exp