There are several organ systems in the body. One of them would be the respiratory system. There are many more including the heart, digestive, and the skeletal.
Can u please add a little more? I don't know anymore.
Agonist/antagonist
Agonist are drugs that bind and activate a receptor with effecting the response.If the effect results in maximum response it is considered as full agonist. However if the drug that binds to the receptor results only into partial efficacy in relation to the full activation of the receptor, this is considered as partial agonist.
Antagonist are drugs that blocks a biologic response of a hormone or another drug. They usually have affinity to the receptors but has no efficacy. This drug will just inhibit the activation of the receptors by the aganist.
The most likely explanation for the variation is the offspring were produced from different combination of genes. A single pair of gold fish mentioned in the question means a male and a female gold fish. The two of them mated and contributed different genes to the fertilized fish eggs, this results in production of various body shape and colouration which is known as variation.
