The use of cage lighting to reduce plasma melatonin in Atlantic salmon (Salmo salar) and its effects on the inhibition of grilsing

Seasonal profiles in growth, energy reserves, gonad development, and plasma steroids in age 1+ cultured Chinook salmon(Oncorhynchus tshawytscha)females

“…Second, solar radiation tends to be more intense in the Southern Hemisphere (McKenzie et al 1996;Sturman & Tapper 1996), so that diel variation in melatonin levels, and the photoperiod regime needed to suppress night time melatonin production, are not necessarily the same in both hemispheres. It is also worth noting that dark phase plasma melatonin levels observed among Chinook salmon in this study were lower (by a factor of 2-5) than for other adult salmonids maintained at similar temperatures (Randall et al 1995;rainbow trout: Yanez & Meissl 1996;Porter et al 1999; Atlantic salmon: Porter et al 2001), despite evidence of a direct relationship between ectotherm melatonin synthesis and ambient temperature (Randall et al 1995;Yanez & Meissl 1996;Porter et al 2001). However, we did not investigate melatonin profiles over a full nocturnal cycle, and it is possible that melatonin production may have increased further had we sampled at midnight.…”

“…A significant reduction in dark phase plasma melatonin levels under the LD 24:0 treatment confirms that, although initiated too late to suppress maturation, the lights were of sufficient intensity to effect a change in melatonin production, and hence in reproductive development (Porter et al 1999). This reduction occurred despite considerable environmental differences between New Zealand and Northern Hemisphere locations such as Scotland and Norway where most research on the effects of supplementary lighting has been conducted.…”

“…We did not expect the LD 24:0 treatment to significantly suppress maturation, as we were unable to install the lights early enough (cf. Porter et al 1999), but took the opportunity to examine its effect on growth, and subsequent reproductive development.…”

“…Research over the last two decades has clearly established that seasonal changes in day length provide the cues which trigger the initiation of maturation in many teleosts, including salmonids (reviewed by Bromage et al 2001). In particular, numerous studies have demonstrated that artificial manipulation of photoperiod can be used to control maturation in salmonids, either by altering its seasonal timing (e.g., Johnson 1984;Duncan et al 1999), or by reducing its incidence (e.g., Hansen et al 1992;Taranger et al 1998;Porter et al 1999). …”

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“…spring or summer and can be stimulated by long photoperiods. There are, however, also fishes, notably salmonids, that spawn in autumn or winter under stimulation by short or declining photoperiods Randal et al, 1995;Porter et al, 1999).…”