Digital Image Analysis as a Technique for Alewife Fecundity Estimation in a New Hampshire River

Abstract

Fecundity estimates are important in fisheries management to determine the reproductive potential and spawning stock biomass of a population. Traditional methods for determining these estimates, however, have been time consuming and tedious, often requiring long-term sample storage in toxic preservatives. Recently, studies incorporated the use of scanners and image analysis software to produce equally reliable fish fecundity estimates. This study was undertaken to demonstrate the application of this technique with Alewife Alosa pseudoharengus, "a species of concern." Ovaries were collected from fish ranging in size from 25 to 34 cm throughout their annual spawning migration (Newmarket, New Hampshire) and used to compare fecundity estimated gravimetrically following long-term storage and by use of a flatbed scanner. Gonadosomatic indices were calculated throughout the collection period but were not found to differ over time. Comparisons within ovaries demonstrated that oocyte size and number did not differ among anterior, center, and posterior sections. Fecundity estimates did not differ between the two methods and increased with fish age and size ranging from 121,000 and 130,200 oocytes/ female (25 cm) to 332,500 and 364,900 oocytes/females (34 cm), respectively. These results demonstrate that fecundity estimates using digital image analysis software were equally reliable as those produced by traditional methods but were generated more quickly and with less reliance on toxic preservatives.

Ovarian dynamics and fecundity regulation in blueback herring, Alosa aestivalis , from the Connecticut River, US

“…Each ovarian subsample was taken from the middle of the ovary. Based on previous results in several alosines (Loesch and Lund, 1977; Olney & McBride , 2002003; Olney et al., 2001; Grice et al, 2014; Sullivan et al, 2019), we considered there were no differences among the anterior, middle and posterior parts of both right and left lobes. Each histological section was digitized into a high‐resolution photomicrograph using a slide scanner (NanoZoomer S60; Hamamatsu Photonics, Japan).…”

Regulation of fish fecundity types in changing environments

“…Additionally, the developmental stage of the measured oocytes was not clearly defined in most of the studies reported in Table 5.2. Sullivan et al 2019 Differences between the two Alewife life-history forms were also observed in onset timing of the spawning season. Spawning activity of the resident populations has incurred a temporal shift towards summer months from the spring spawning strategy of their ancestral, anadromous form.…”

“…However, comparisons among Alewife populations should be made with caution. For instance, Jessop (1993) and Sullivan et al (2019), prior to OD estimations, preserved the oocytes in Gilson's fluid, which is known to cause pronounced oocyte shrinkage (Joseph 1963;Klibansky and Juanes 2007). Additionally, the developmental stage of the measured oocytes was not clearly defined in most of the studies reported in Table 5.2.…”

“…Some aspects of Alewife reproductive biology have often been examined and for various populations, such as timing of spawning run, spawning season and annual egg production (e.g., Norden 1967;Kissil 1974;Ellis and Vokoun 2009;Sullivan et al 2019).…”

“…This step was skipped in this study, since such differences have not been detected in several alosines(Mayo 1974;Loesch and Lund 1977;Olney et al 2001; Olney and McBride 2003;Grice et al 2014;Sullivan et al 2019) and other clupeids(Hunter et al 1985;Sanz and Uriarte 1989;Pérez et al 1992;Ganias et al 2004) …”