Growth and length-weight relationship of the striped marlin, Tetrapturus audax (Pisces: Istiophoridae),

Age and growth of the sailfish Istiophorus platypterus were determined for the area off Mazatlan coast, Sinaloa, in the Gulf of California, between September 2002 and August 2003. The lower jaw-fork length and total weight of 572 specimens were measured, and the fourth dorsal spine was collected to determine age. The monthly variation of the sample size displayed a well-defined seasonal pattern, which peaked during the warm period (May-November) and declined during the rest of the year (temperate period). Significant differences were detected in the size structure by sex during the temperate period, with females displaying larger sizes and greater abundance (Female: Male = 3.35:1). In the warm period the size structure was similar, with the sex ratio reaching F:M = 0.73:1. This suggests a different sex-related recruitment in the fishing zone, with males moving more actively than females. While female size remained relatively unchanged over the year, male size increased during the warm period. Age was estimated using the number of growth rings on the cross-sectioned fourth dorsal spine, after the number of absorbed growth rings in the vascularized zone had been estimated. Nine age groups were identified; group-5 was the most abundant, representing 31% of the catch. The trend of the monthly change in the percentage of opaque-edge spines and the average of the marginal increase rate indicated that the formation of growth rings displayed an annual pattern. The von Bertalanffy growth model was adequately fitted to age and back-calculated length data. Significant differences were detected when growth was compared between sexes; females grew faster than males.

-Determining age is an important step when assessing growth, mortality, and yield of cultivated and wild populations, but studies linking shell growth marks in the pearl oyster Pteria sterna with the age of individuals are lacking. Thirty juveniles (20.0 ± 1.2 mm shell height), collected from a winter spatfall, were marked with the fluorochrome calcein and kept in the field in culture containers. After day 16, the juveniles were cleaned and their shells cut along the sagittal axis to determine periodicity of micro growth bands formed in the inner shell layers and to estimate age. During this trial, fluorescent calcein marking succeeded in individuals larger than 20 mm shell height; these formed an average of 15 micro growth bands over the 16 days, representing 1 band per day. The marker created a wide fluorescent band containing three micro growth marks, suggesting that calcein was incorporated into the shell over the first three days. The use of calcein was found to be an accurate method for validating the micro growth band frequency of formation in P. sterna juveniles, which in turn can help to estimate age.

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