Salinity and photoperiod modulate pubertal development in Atlantic salmon (Salmo salar)

Area of Science:

• Aquaculture and Fish Reproduction
• Endocrinology and Environmental Physiology
• Molecular Biology and Gametogenesis

Background:

• Atlantic salmon exhibit life cycle plasticity, including puberty timing.
• Environmental factors like salinity and photoperiod influence fish puberty.
• Key aspects of puberty and their environmental regulation in fish remain unclear.

Purpose of the Study:

• To investigate the effects of salinity and photoperiod on Atlantic salmon puberty.
• To analyze the impact of freshwater vs. seawater and constant light vs. light-dark cycles on reproductive gene expression and spermatogenesis.
• To understand the differential roles of environmental cues in stimulating and completing spermatogenesis.

Main Methods:

• 12-month-old Atlantic salmon were exposed to four conditions: freshwater/light-dark (FWLD), freshwater/constant light (FWLL), seawater/light-dark (SWLD), and seawater/constant light (SWLL).
• Measurements included plasma 11-ketotestosterone (11-KT) levels, pituitary gene expression (gnrhr4, fshb, lhb), and spermatogenesis.
• Spermatogenesis was assessed by quantifying germ cell stages and proliferation.

Main Results:

• Seawater exposure significantly enhanced the onset of spermatogenesis and elevated pituitary gnrhr4 and fshb mRNA levels.
• A 12h light:12h darkness photoperiod accelerated spermatogenesis completion, regardless of salinity.
• Accelerated completion correlated with increased lhb mRNA and 11-KT plasma levels compared to constant light groups.

Conclusions:

• Salinity and photoperiod differentially modulate Atlantic salmon spermatogenesis.
• Seawater stimulates the initiation of spermatogenesis, while a shorter photoperiod promotes its completion.
• These findings highlight the complex interplay between environmental factors and the regulation of puberty in fish.