Here's why:
* Genetics play a major role: Goldfish colour development is heavily influenced by genetics. Some varieties naturally take longer to develop their full colour than others. For example, some fancy goldfish breeds like the Oranda or Ranchu can take years to fully mature in colour.
* Environmental factors: Water quality, diet, and lighting can also influence colour development. A goldfish raised in poor conditions might develop its colour more slowly than one raised in optimal conditions.
* Individual variation: Just like humans, goldfish have individual variations. Some fish from the same brood might develop their colour faster than others.
It's important to consider:
* Breed: Research the specific breed of goldfish you have to understand their typical colour development timeline.
* Age: Goldfish can continue to develop colour over several years, especially fancy goldfish.
* Overall health: If a goldfish is healthy and well-nourished, it should develop its colour according to its genetics.
If you are concerned about your goldfish's colour development, consult a reputable aquarist or veterinarian. They can help you assess the situation and determine if there are any underlying issues.