How Do You Age a Fish?<\/h1><\/div><\/div><\/div><\/div><\/div><\/div><\/div>Last week, a handful of the TBS crew attended a two-day workshop on fish ‘ageing,’ <\/b>generously hosted by Florida Fish and Wildlife Conservation Commission<\/a><\/b> and led by fish ageing expert and researcher, Kristin Cook.<\/b>\u00a0TBS graduate students Kylee Rullo and Alexandra Lee, laboratory technician Daisy Wischmeyer, and program planner Roxann Vistocci learned how to prepare<\/b> otoliths, cut<\/b> otoliths, and mount<\/b> otolith cross sections onto microscope slides before analyzing and ageing. So, what’s an otolith?<\/b><\/p>\nAn otolith is a <\/span>fish’s ear bone<\/b><\/span>, a small calcium carbonate structure located within the inner ear of bony fish, and is used as a primary <\/span>tool for determining a fish’s age<\/b><\/span>. Otoliths exist in three pairs and vary in form. Beyond determining age, otoliths play a crucial role in a fish’s hearing, vibration detection and balance – enabling fish to navigate waters effectively. (NOAA Fisheries, 2025<\/a>)<\/span><\/p>\nThroughout a fish’s life, otoliths grow by adding layers of material around a central core. These layers alternate between opaque and translucent appearances<\/b>, reflecting changes in growth rate. A wider, opaque layer forms during periods of active feeding, typically in warmer months, as the fish’s diet provides abundant calcium. Conversely, a narrower, translucent layer develops when feeding is reduced, which indicates slower growth. A complete cycle<\/b> of an opaque and translucent layer represents one year of growth<\/b>, known as an annulus<\/b>. (NOAA Fisheries, 2025<\/a>)<\/p>\n<\/div><\/div><\/div>![](\"https:\/\/www.marine.usf.edu\/tbs\/wp-content\/uploads\/2025\/03\/kristin-points-to-otolith-details-tbs-training-scaled.jpg\")
<\/span>FWC researcher, Kristin Cook (right, front), points to a fish otolith as Kylee (seated), Alexandra (l) and Daisy (r) look on.<\/p><\/div><\/div><\/div><\/div><\/div><\/div><\/div>
Check out otoliths from a red drum<\/b> (left) and a spotted seatrout<\/b> (right) in the videos below.<\/p>\n<\/div><\/div><\/div>
Last week, a handful of the TBS crew attended a two-day workshop on fish ‘ageing,’ <\/b>generously hosted by Florida Fish and Wildlife Conservation Commission<\/a><\/b> and led by fish ageing expert and researcher, Kristin Cook.<\/b>\u00a0TBS graduate students Kylee Rullo and Alexandra Lee, laboratory technician Daisy Wischmeyer, and program planner Roxann Vistocci learned how to prepare<\/b> otoliths, cut<\/b> otoliths, and mount<\/b> otolith cross sections onto microscope slides before analyzing and ageing. So, what’s an otolith?<\/b><\/p>\n An otolith is a <\/span>fish’s ear bone<\/b><\/span>, a small calcium carbonate structure located within the inner ear of bony fish, and is used as a primary <\/span>tool for determining a fish’s age<\/b><\/span>. Otoliths exist in three pairs and vary in form. Beyond determining age, otoliths play a crucial role in a fish’s hearing, vibration detection and balance – enabling fish to navigate waters effectively. (NOAA Fisheries, 2025<\/a>)<\/span><\/p>\n Throughout a fish’s life, otoliths grow by adding layers of material around a central core. These layers alternate between opaque and translucent appearances<\/b>, reflecting changes in growth rate. A wider, opaque layer forms during periods of active feeding, typically in warmer months, as the fish’s diet provides abundant calcium. Conversely, a narrower, translucent layer develops when feeding is reduced, which indicates slower growth. A complete cycle<\/b> of an opaque and translucent layer represents one year of growth<\/b>, known as an annulus<\/b>. (NOAA Fisheries, 2025<\/a>)<\/p>\n<\/div><\/div><\/div> FWC researcher, Kristin Cook (right, front), points to a fish otolith as Kylee (seated), Alexandra (l) and Daisy (r) look on.<\/p><\/div><\/div><\/div><\/div><\/div><\/div><\/div> Check out otoliths from a red drum<\/b> (left) and a spotted seatrout<\/b> (right) in the videos below.<\/p>\n<\/div><\/div><\/div><\/span>