Physiology
A
Age and Growth
Quick Definition
The study of how fish age is determined and how body size changes over time, fundamental to stock assessment and life-history analysis.
📖 Full Definition
Age determination in fish is performed primarily by counting annual growth rings (annuli) on calcified hard parts: otoliths (most accurate, especially for older fish), scales, fin rays, and vertebrae. Growth increments reflect seasonal feeding cycles — rings are wider in summer (fast growth) and narrower in winter (slow growth), producing an annual banding pattern analogous to tree rings. Daily growth increments (microincrements) are visible in early life stages and are used to determine hatch dates and larval growth rates.
💡 Examples & Context
Orange roughy (Hoplostethus atlanticus) were thought to live to 30 years when deep-sea trawling began in the 1970s; radiometric dating of their otoliths later revealed they live to 150+ years and mature at 25–30 years — making them catastrophically vulnerable to the intense fishing that had already begun.