Читать книгу Clinical Guide to Fish Medicine - Группа авторов - Страница 130

Light intensity, spectrum, and photoperiod are important parts of the life support system. Lighting impacts feeding, reproduction, and behavior. A review of 38 species of Hawaiian fish demonstrated the great variety of visual sensitivities. Spectrums varied between 347–376 nm (ultraviolet) and 439–498 nm (blue light) and vision was affected by the lenses, corneas, and humors (Losey et al. 2003). It is important to understand the spectral needs of the fish species being housed to maximize welfare. Excess light intensity can lead to sunburn and cataracts. Scala et al. (2016) found retinal neoplasms in hybrid striped bass (Morone saxatilis) and pajama cardinalfish (Sphaeramia nematoptera) housed in systems with high‐energy blue light produced by metal halide lamps. And some fish show bioluminescence or phosphorescence that is strongly impacted by lighting. Not only does one have to consider animal welfare, but lighting also has aesthetic effects that are particularly important in display aquariums.

Figure A3.17 Rubber bushings for mounting of pumps to minimize noise and vibration.

Water filters the light spectrum, absorbing red light within the first few centimeters. The aquarium professional tries to recreate natural environments through manipulation of lighting, e.g. high intensity for shallow tropical reefs, blue for deep‐water habitats, or infrared for complete darkness. With mixed species habitats, it is hard to target lighting to each species.

The need for full spectrum lighting for fish has been a topic of debate. In particular, the need for UVB remains controversial. UVB penetration depth is mainly influenced by water turbidity and the number of photons contacting the water. In the ocean, only ~10% of surface UVB can penetrate down to 35 m at full sunlight with minimal total organic carbon in the water (Aas and Højerslev 1999). A major challenge for large aquariums is the permeation of light using artificial bulbs. Bulbs have a high energy output and lose light intensity with distance due to the inverse square law of light (light intensity is inversely proportional to the square of the distance from the source point). The longer the distance, the less intense the light.

Results of UVB application to aquatic systems have been mixed. Three 160‐W UVB heat lamps (T‐Rex® Active UV Heat) placed 91 cm above the water surface produced a UVB intensity of 0.1 ± 0.05 mJ/cm² or mWs/cm² but only over a surface area of 3.8 cm diameter directly below each lamp, despite observing a larger light footprint. A 50% variation in UVB intensity was also observed between each bulb. Additionally, light intensity degraded rapidly within the normal six‐month replacement cycle (Purgley et al. 2009). A similar study involved a Mega‐Ray® 275 watt Self‐Ballasted Flood UVB Lamp placed 61 cm above a tank with a diameter of 305 cm and depth of 183 cm. This produced a UVB intensity ~0.015–0.050 mJ/cm² over a quarter of the tank and caused dermatitis in fish cohabitating with sea turtles after eight hours of exposure (Boylan pers. comm.).

A critical aspect of light is photoperiod. At a minimum, fish should be exposed to relatively steady photoperiods without sudden changes. This can be difficult in display aquaria where there is often demand for exhibit lighting during evening events. And to mimic natural diurnal cycles and prevent startling, periods of lower intensity at the start and end of the light period should be used to mimic dawn and dusk. Ideally, photoperiod should mimic natural seasonal changes for the species. Species‐appropriate light refuges should be provided to allow inhabitants choice.