Fishes -- Reproduction, Poeciliidae


In Poecilia latipinna size-specific reproductive and survivorship patterns were correlated with changes in habitat availability. Of the numerous physical, chemical, and biological parameters associated with a reduction in available habitat, probably the most important was reduced food availability. Large (old) females, theoretically with a low reproductive value, allocated energy to reproduction regardless of habitat and, presumably, food availability. When reproductive activities were initiated in March, habitat availability was modest. In association with a severe reduction in available habitat in April, large females were subject to a substantial loss of body weight during the yolk-loading phase of the reproductive cycle. This loss, primarily of somatic tissue, was very costly and heavy mortality ensued. Habitat availability increased during late May and June and survivorship increased. By August the somatic condition of large females had improved significantly. As in April, yolk-leading resulted in a loss of body weight; however, the loss consisted of approximately 70% lipid. Although the cost was lower than April, the necessity of subsidizing reproduction with somatic tissue may account for the slight reduction in survivorship observed in September. Smaller (younger) females, theoretically with a higher reproductive value, allocated energy to reproduction in response to increases in habitat, and presumably food availability. This response was in the form of an increased number of small reproducing females and was not evident until the month following the increase in available habitat. In contrast to large females, reproductive activities among small females were initiated in April. In association with a severe reduction in habitat availability, small females were subject to a loss of dry weight during yolk-loading, which consisted of approximately 44% lipid. The cost of reproduction was reduced and survivorship improved relative to the large females. Despite an increase in available habitat in June, small females curtailed reproduction in favor of survival and increased fecundity afforded by a greater body size. By early August an increase in reproductive activities was evident among small females. The somatic condition of these females was significantly improved in comparison to April females. In contrast to large August females, small females did not subsidize reproduction with somatic tissue. The change in body weight was attributable to a loss of lipid. By early September the available habitat had increased dramatically. In comparison to August, the high number of small reproducing females suggested the response to improved conditions may be rapid. Changes in food availability and, thus the total energy budget (lower in spring, higher in the summer and fall) and the associated cost of reproduction (higher in spring, lower in fall) from April to September were not reflected by changes in fecundity. It appeared that under the conditions that prevailed during this study, a female that made a commitment to reproduction produced a size-specific brood of a fixed quality regardless of food availability and reproduction cost. If a female was able to assimilate excess energy during the gestation period, that energy was allocated in maintenance (i.e. repaying any somatic debt) and growth.


If this is your thesis or dissertation, and want to learn how to access it or for more information about readership statistics, contact us at

Graduation Date

Summer 1982


Snelson, Franklin F.


Master of Science (M.S.)


College of Arts and Sciences

Degree Program





44 p.




Public Domain

Length of Campus-only Access


Access Status

Masters Thesis (Open Access)



Contributor (Linked data)

Snelson, Franklin F. [VIAF]

Snelson, Franklin F. [LC]

Accessibility Status

Searchable text

Included in

Biology Commons