Variable Growth and Longevity of Yellow Bullhead (Ameiurus natalis) in South Florida

Revised Final Report by

October 2006

Abstract

To determine age and growth of yellow bullheads (Ameiurus natalis), we collected fish from canals and marshes in southern Florida from April 2000 to January 2001, and from Oct 2003 to February 2005. Fish ranged from 97 to 312 mm in total length and from 13.4 to 538.1 g in wet mass. We aged 144 yellow bullheads using cross-sections of pectoral spines and a subsample of 55 fish were aged using sanded and polished cross-sections of lapillar otoliths. Pectoral-spine age estimates had relatively high precision between two experienced readers (average percent error [APE] = 6.1%, CV = 8.6%), with 65% of ages having perfect agreement and 92% agreeing within ±1 year. Lapillar-otolith age estimates provided inadequate precision with high APE (16.8%) and CV (23.7%), and low percent agreement (25% perfect agreement and 61% within ±1 year). Annuli in lapilli were not clearly demarcated and were not evident in all cross-sections of the otoliths; moreover, longitudinal sections of lapilli were unreadable. Precision estimates in comparing ages between pectoral spines and otoliths also indicated aging difficulties, with an APE of 20.6% and a CV of 29.1%. Determining ages by using cross-sections of lapilli was therefore not reliable for yellow bullheads in southern Florida, and so we did not use otolith age estimates as input into the growth model. The pectoral-spine aging method was validated using oxytetracycline (OTC)-injected yellow bullheads, which were found to deposit one complete annulus (one translucent and one opaque zone) over a 12-month period. Yellow bullheads from south Florida ranged in age from 1-12 years based on aging using pectoral spines; and therefore had a maximum age that was double that previously reported for any other yellow bullhead population. Yellow bullheads grew relatively rapidly in their first 3 years, but after age 5 their growth slowed and approached an asymptote of ~214 mm total length. Yellow bullheads in south Florida grew relatively slowly and were smaller compared to yellow bullheads from other populations throughout the United States.

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