The threshold of light intensity and sensitivity to light clearly vary
between species and probably stage of development. Direct comparisons
are not straightforward due to the lack of standardisation in the
unit of light measurement (lux, watts, photon flux….), the use of
various light sources with very different spectral compositions
(halogen, tungsten, LED…), the range of rearing systems (tank
dimensions) and husbandry protocols (green vs clear water) used
depending on species and sites. For all these reasons, our knowledge of
species-specific (and stage of development) light intensity sensitivities
is still scarce and comparative studies using standardised
conditions, protocols and lighting systems are clearly needed.
Importantly, when studying light, measurements have to consider
the full visible spectrum and not only what the human eye can detect.
Therefore, the use of measurement units specific to the spectral
sensitivity of the human eye (Lumens, lux etc.) is not appropriate and
should be replaced by unbiased irradiance measurements like watts/
m2 or photons/s/m2. Table 2 provide definitions and light unit
conversions. To date, there are no standardised lighting protocols
used by the industry in any of the commercially important marine
species. Furthermore, many published scientific studies looking at
marine larvae performances do not state experimental light intensities
tested.
Downing and Litvak (1999) reported that larval haddock (Melanogrammus
aeglefinus) performed better at medium light intensities
(3.15 mu mol s−1 m−2), with increased feed intake when exposed to
blue light. The authors concluded that at this intermediate intensity,