Determining morhpological and biochemical parameters associated with ovarian follicular atresia and caviar quality and yield in cultured white sturgeon (Acipenser transmontanus)

Abstract

Harvesting sturgeon Acipenseridae when the ovarian follicles have the appropriate firmness and size is important for the caviar industry in order to produce a consistently uniform product and maximize caviar yield. Therefore, it is beneficial for the caviar industry to detect fish with atretic ovarian follicles prior to harvest, which can cause a decrease in caviar grade or complete loss of the product and to harvest fish at the correct stage of ovarian maturity to produce the highest quality and yield of caviar possible. The objectives of this study were to find a parameter that can detect early signs of ovarian follicular atresia by measuring blood plasma concentrations of sex steroids and determine if correlations exist among plasma sex steroid concentrations, morphological characteristics, and caviar yield and quality. To achieve the first objective, blood and ovarian follicles were collected repeatedly from 15 fish prior to and after inducing follicular atresia. Plasma testosterone (T) was the best indicator of the onset of atresia. Logistic regression models were used to illustrate how a threshold value of T can be determined to decrease the probability of harvesting white sturgeon with atretic ovaries. To achieve the second objective, biological samples (blood, ovarian follicles) and morphological measurements were collected from white sturgeon at caviar harvest (n = 20 per month) for five months. Analyses of parameters associated with caviar quality were limited because 92% of fish produced the same quality of caviar. Plasma E2 was correlated with caviar yield, caviar yield as a percent of body weight, and gonadosomatic index (GSI), whereas T was not correlated with either caviar yield or caviar yield as a percent of body weight. Ovarian fat varied greatly among individuals. Consequently, the ovarian stage associated with caviar yield could not be determined by measuring morphological parameters indicative of ovarian maturity. Post-hoc analyses were conducted to determine if parameters differed among ovarian fat categories. In the future, this study may benefit sturgeon conservation propagation programs by improving techniques for detection of ovarian atresia and offering a less-invasive method for estimating fecundity by utilizing the correlation between plasma E2 and GSI.