The reproductive success of fish is intricately linked to environmental factors, which regulate the hypothalamic-pituitary–gonadal (HPG) axis and influence gonadal development, gamete production, and spawning. Key environmental parameters such as photoperiod, temperature, pH, alkalinity, hardness, dissolved oxygen (DO), turbidity, and nitrogenous compounds (ammonia, nitrate, nitrite) play critical roles in fish reproduction. These factors significantly impact reproductive functions, including gonadal growth and maturation, gamete cell development, hatching rates, and larval survival. Unfortunately, hatchery experts and fish farmers often overlook these parameters, leading to suboptimal seed production and lower-quality fish stocks. This review discusses the various environmental parameters and their effects on gonadal development and reproductive performance in fish particularly at the molecular level. Understanding these factors can help researchers differentiate the impact of environmental variables from other influences like feed quality and genetic factors, ultimately leading to better management practices in fish breeding and seed production.