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Wet Lab Sample Processing
|Brown Shrimp||Greater Blue Crab||Juvenile Atlantic Croaker|
Target fish (those deemed to be commercially and/or recreationally important) are brought back to the laboratory for further processing. Target fish are measured down their centerline, weighed, otoliths extracted, sex is determined, and if female then the ovaries are weighed. The otoliths are extracted because this bony structure is the most reliable way to determine a fish's age.
Otoliths are located in the otic capsule of the head and are used by the finfish to interpret sensory information regarding movement, orientation, momentum, and sound. Daily growth of the otoliths lay down rings. Times of slower growth, associated with cooler months, causes rings to lay down in a more compact manner forming dark (opaque) rings. These thick rings are referred to as annuli. Faster growth periods, associated with warmer months, cause rings to lay down farther apart giving a translucent appearance. One translucent and one opaque ring are equivalent to one year's growth.
Otoliths must be thinly sectioned and mounted on a microscope slide to determine the number of annual growth zones present. AMRD personnel use a Hillquist Thin Section Machine and shave the otolith down to less than 1cm of thickness and cover the sectioned otolith with a clear liquid to prevent moisture from the air deteriorating the otolith section. After the otolith has been sectioned and mounted on a slide a Gulf States Marine Fisheries Commission (GSMFC) trained otolith reader will determine the age of the fish. The age of the fish can then be correlated with the length and sex to help determine size and creel limits.
Otoliths are processed at both the Gulf Shores and Dauphin Island offices. For further information regarding otolith collection and processing contact Karon Aplin (Gulf Shores) or Jaime Miller (Dauphin Island).
|Extracted Otolith from a Red Drum||Otolith Processing||Section Red Drum Otolith|