The reproductive characteristics of six geographically isolated populations (n = 1150) of Spotted Sand Bass, Paralabrax maculatofasciatus, from throughout their natural range were studied from April 1992 to July 1994. Histological examination of gonads revealed the following: (1) a membrane-lined cavity or gonadal lumen was present in 9% of all males observed in this study, being present in the San Diego Bay, Los Pulpos, and Guerrero Negro populations; (2) sperm sinuses containing developing sperm were present in 65% of all females in the Anaheim Bay, Newport Bay, San Diego Bay, Los Pulpos, and Magdalena Bay populations; (3) atretic or yellow bodies were present in 76% of all males; and (5) five transitional individuals were found in the Los Pulpos and San Diego Bay populations. Both primary and secondary males were represented in all populations indicating diandric origin of males. Analysis of sex frequencies by age class and by length class for the San Diego and Los Pulpos populations showed a bimodal distribution indicative of protogynous hermaphroditism. Specimens from Anaheim Bay and Newport exhibited patterns more typical of a gonochoric reproductive pattern, whereas the Guerrero Negro and Magdalena Bay populations exhibited intermediate patterns. Only the spotted sand bass populations from San Diego Bay and Los Pulpos exhibited trends typical of protogynous hermaphroditism in both the histological and age/length population structures. Therefore, the reproductive patterns observed in the six populations of spotted sand bass are best represented by a spectrum ranging between gonochorism and protogynous hermaphroditism. The key to this diverse spectrum of strategies may be the ability of females to change sex, to delay sex change to later in life, or not to change sex at all. This reproductive plasticity also allows the females to maximize their reproductive fitness regardless of population size, breeding site densities, and accompanying mating systems.

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