Spawning and fecundity of Jenyns's sprat, Ramnogaster arcuata, a winter spawner in the temperate waters of the Río de la Plata estuary, Argentina–Uruguay

Abstract

The reproductive biology of the Jenyns's sprat Ramnogaster arcuata in the Río de la Plata area was studied using macroscopic and histological analysis of ovaries. Samples were collected during two research surveys carried out in June 1998 and June 1999. In addition monthly occurrences of this species from historical data were analysed. Jenyns's sprat specimens were mainly observed in open waters of the estuary during winter months. Most of the females collected during June 1998 and 1999 were in the spawning stage. This pattern differs from fish that reproduce in the estuarine waters of the Río de la Plata, which spawn during spring and summer. These results suggest that conditions of productivity and larval retention in the estuary also remain during winter months. This characteristic might be useful for R. arcuata larvae in avoiding competition with other estuarine spawners. Jenyns's sprat is a multiple spawner with indeterminate annual fecundity. A preliminary estimate of spawning frequency (N ¼ 220) indicated a daily percentage of females with postovulatory follicles of 17.35%, which suggests that this species spawns on average once every six days. Batch fecundity, estimated from counts of hydrated oocytes from 40 females, ranged from 669 to 2026 hydrated oocytes in 1998 and from 570 to 1830 hydrated oocytes in 1999. Batch fecundity was fitted to a linear function of total body weight (without ovary) in 1999. Mean relative fecundity was 234 hydrated oocytes per female gram (ovary free) in 1998 and 155 hydrated oocytes per female gram (ovary free) in 1999, and no significant relationship was observed between this parameter and female size. The dry weight of 100 hydrated oocytes ranged between 3.9 and 6.3 mg, these values being significantly higher than those estimated for other species of the Río de la Plata estuary.

Reproductive studies of Anchoa marinii Hildebrand, 1943 (Actinopterygii: Engraulidae) in the nearby-coastal area of Mar Chiquita coastal lagoon, Buenos Aires, Argentina

“…As far as we know, this represents the first contribution to fecundity estimates for the species. These values were higher when compared with those obtained for R. arcuata (570-2,026; 75-116 mm TL) (Rodrigues et al, 2008), but lower than the Buenos Aires stock of E. anchoita (Pájaro et al, 1997) (13,675 +/-856; 100-189 mm TL). The relative fecundity values ranged from 127 to 422 yolked oocytes per female gram (ovary free).…”

“…The oocyte diameter distribution of A. marinii showed four clutches/ groups of oocytes easily differentiable in histological slides (between 50 and 650 µm) and ovaries displayed a continuous distribution from primary growth to advanced yolked oocytes. In R. arcuata, Rodrigues et al (2008) found five groups of oocytes. The first four groups, as in A. marinii, showed a continuous distribution and were composed of primary growth oocytes, cortical alveolus stage, early yolked oocytes and advanced yolked oocytes.…”

“…Batch spawner has been suggested for other Clupeiform species, i.e. Engraulis anchoita (Brodsky & Cousseau, 1979), Ramnogaster arcuata (Rodrigues et al, 2008) and Brevoortia aurea (Macchi & Acha, 2000). The oocyte diameter distribution of A. marinii showed four clutches/ groups of oocytes easily differentiable in histological slides (between 50 and 650 µm) and ovaries displayed a continuous distribution from primary growth to advanced yolked oocytes.…”

Reproduction of Brevoortia aurea (Spix & Agassiz, 1829) (Actinopterygii: Clupeidae) in the Mar Chiquita Coastal Lagoon, Buenos Aires, Argentina

“…For example, batch fecundity estimated of Anchoa marinii was 749 to 3,207 oocytes, (López et al, 2013). Rodrigues et al (2008) reported a batch fecundity of 570-2,026 oocytes for Ramnogaster arcuata specimens. Pájaro et al (1997) reported a fecundity of 13,675 oocytes (+/-856) for Engraulis anchoita.…”

“…However, when comparing the relative fecundity of these species, it is noticeable that B. aurea presented the lowest values in comparison with those of the above mentioned species: 41-381 hydrated oocytes per gram of female (ovary free) for B. aurea, 127-422 oocytes for A. marinii (López et al, 2013); R. arcuata between 150 and 437 oocytes (Rodrigues et al, 2008) and E. anchoita with 574 oocytes (Pájaro et al, 1997). These differences could be due to the largest size of the hydrated oocytes of B. aurea (1000 to 1600 μm in this paper), in comparison with other local species of Clupeiformes (A. marinii; R. arcuata and E. anchoita) which are less than 1000 μm (Rodrigues et al, 2008;López et al, 2013;Pájaro et al, 1997). The size and number of eggs produced vary greatly among species and all of these traits have important consequences for survival.…”