Criteria for Determining Maturity Stage in Female American Shad, Alosa Sapidissima, and a Proposed Reproductive Cycle.

Abstract

We describe macro-and microscopic criteria to judge maturation stages of female American shad (Alosa sapidissima) collected in the York river, Virginia, USA. For comparison, we also examined ovaries of fishes collected in the Edisto river, South Carolina, and the Connecticut river, Massachusetts. The study augments a developing stock assessment program that is evaluating the use of index-removal and change-in-ratio estimators of exploitation rate and absolute abundance. Samples were obtained from traps at the York river mouth, staked gill nets in mid-reaches of the river, and drift gill nets on the spawning grounds (approximately 100 km from the river mouth). To judge maturation stages, we used the following macroscopic characters : ovary color, gross appearance of oocytes, degree of blood infusion, and value of the gonosomatic index (ovary weight divided by somatic weight). Stain reactions and presence or absence of cellular characteristics (nucleoli, nuclear migration, oil globules, yolk vesicles, atresia, and postovulatory follicles) were used as microscopic criteria. No differences in scoring of maturation stage were observed in comparisons of samples from different regions of the ovary. American shad in both semelparous (Edisto river) and iteroparous populations (York and Connecticut rivers) exhibit indeterminate fecundity and group-synchronous oocyte development. Unyolked, partially yolked and advanced yolked oocytes are observed in all maturity stages except spent females. There is histological evidence that an individual female spawns in batches over a period of days or weeks since both recently developed and older post-ovulatory follicles are observed simultaneously with advanced yolked oocytes. Most post-spawning females captured at the river mouth are only partially spent with ovaries that contain large numbers of advanced oocytes. A reproductive cycle for American shad in the York river is proposed. Successive or batch spawning in wild populations has important ecological implications since an individual can spread her gametes over a large spatio-temporal scale, thereby increasing the chances that progeny will encounter salubrious conditions. Key RnSUMnNous décrivons des critères macro et microscopiques pour juger des stades de maturité des aloses américaines femelles (Alosa sapidissima) captur¡es dans la rivière York, Virginia, USA. A titre de comparaison, nous examinons également des ovaires de poissons capturés dans la rivière Edisto, South Carolina, et dans la rivière Connecticut, Massachusetts. L'étude fait partie d'un programme en cours d'évaluation de stocks, qui utilise la méthode des changements de proportions et de la méthode des changements d'indices d'abondance par prélèvement pour estimer le taux d'exploitation et d'abondance absolue. Des échantillons ont été obtenus grâce à des trappes à l'embouchure de la rivière York, des filets fixes (à mi-parcours migratoire) et des filets dérivants sur les lieux de ponte (à environ 100 km de l'embouchure). Afin d'établir les stades de matu...

Gross and histological observations of ovarian development in twaite shad, <i>Alosa fallax fallax</i>, from Rivers Mira and Guadiana (Portugal)

“…This is supported by the lack of a hiatus in the size frequency distribution of immature versus mature oocytes. Similar results were also reported for twaite shad by Le Clerc (1941) and Hass (1968) and for American shad, A. sapidissima, by Mylonas et al (1995) and Olney et al (2001).…”

“…The process of oocyte development in A. fallax fallax follows the same basic progression as that described for Alosa sapidissima (Mylonas et al, 1995;Olney et al, 2001) and other teleost fish (Tyler and Sumpter, 1996).…”

“…The spawning season can last until June (Pina, 2000). Several studies have been undertaken on Alosa spp., mainly regarding age and growth (Walburg, 1960;Mennesson-Boisneau et al, 1986), migration patterns (Rameye et al, 1976;Loesch, 1987;Quinn And Adams, 1996), reproduction (Hoestlandt, 1958;Walburg, 1960;Nichols and Massmann, 1963;Loesch and Lund, 1977;Leggett and Carscadden, 1978;Loesch, 1987;Manyukas, 1989;Jessop, 1993;Ross et al, 1993;Mylonas et al, 1995;Pina, 2000, Olney et al, 2001, and recruitment (Johnson and Loesch, 1983;Esteves, 1999). However, published information on the reproductive biology of A. fallax is restricted to the accounts of Manyukas (1989), Quignard and Douchement (1991) and Pina (2000), which provide no detailed description of the histological development of the gonads.…”

Spawning dynamics of American shad (Alosa sapidissima) in the St. Lawrence River, Canada–USA

“…Under high levels of variance in mortality of the youngest life-history stages, such iteroparity forms part of the bet-hedging reproductive strategy that trades off a higher mean fitness in favour of a lower variance in fitness under environmental uncertainty (Philippi & Seger 1989). In American shad, batch spawning has been observed in both semelparous (Edisto River) and iteroparous (York and Connecticut Rivers) populations (Olney et al 2001). In American shad, batch spawning has been observed in both semelparous (Edisto River) and iteroparous (York and Connecticut Rivers) populations (Olney et al 2001).…”

“…Another manifestation of bethedging is batch or serial spawning, whereby females spawn on several occasions and at different sites during the same reproductive season. These authors proposed that batch spawning increases the probability of finding favourable conditions for the survival of the most vulnerable lifehistory stages by dispersing them over greater spatial and temporal scales (Olney et al 2001). Evidence for batch spawning is based on the simultaneous observation of developing and postovulatory follicles in females captured at different points in their migration.…”