FISH is the acronym for first-in, still-here. FISH is an attempt to bring humor to the fact that some items have been sitting in inventory for years.
If the same items have been sitting in inventory for years, there are potential accounting issues. For example, the value of the items may be less than their costs due to obsolescence or deterioration. In addition, the company continues to incur other costs of holding inventory such as the cost of capital, space, insurance, etc.