Reproductive cycle of the sea cucumber (Isostichopus fuscus) and its relationship with oceanographic variables at its northernmost distribution site

Abstract

The brown sea cucumber Isostichopus fuscus is highly prized and intensively fished, yet no studies of its reproductive cycle at its northernmost distribution site exist. To characterize its reproductive cycle, monthly surveys (Oct 2014-Dec 2016) that included gonad collection were conducted in 118 sites along the eastern coast of Baja California, including islands from Bahía San Luis Gonzaga (29o 49’ 14.18” N, 114 o 3’56.17” W) to the 28th parallel north. A total of 2 808 sea cucumber specimens were measured (mean length ± SD = 21.4 ± 6 cm) and weighed (375.6 ± 249 g). Seven hundred and seventeen organisms were dissected but only 553 gonads were suitable for processing through histological analysis to identify sex and developmental stage. Of these individuals, 224 were female, 162 were male, 157 were undifferentiated and 10 were hermaphrodites, resulting in a sex ratio that was significantly different from 1:1 (χ2 = 36.63, P = 0.03, df = 23). There was no statistical difference (p > 0.05) of either size or weight between males and females, but females were larger than males. The length-weight relationship observed was W = 0.18L2.4, r2 = 0.82, p <0.05 while the size-at-first-maturity was 16 cm. Five gonad stages were identified: 28% undifferentiated, 9% gametogenesis, 15% mature, 19% expulsion and 29% post-expulsion. The Oocyte Theoretical Diameter (OTD) was estimated by measuring the area of 10 291 oocytes, finding 2 307 individuals in oogenesis (mean ± SD of 65.3 ± 19.7 µm), 3 630 in maturity (66.0 ± 17.8 µm), 3 756 in spawning (73.8 ± 14.6 µm) and 868 in post-spawning (49.18 ± 20.7 µm). Modal progression analysis shows that oocytes increase 23% in size from oogenesis to maturity, and decrease 9%in size from maturity to spawning and, on average, oocytes are 72% smaller post-spawning that during spawning. Rev. Biol. Trop. 65(Suppl. 1): S180-S196. Epub 2017 November 01.

Reproductive cycle of the sea cucumber Holothuria forskali (Holothuriida: Holothuriidae) in the Ría de Vigo (NW of Spain)

“…Shiell & Uthicke (2006) also found that in Holothuria whitmaei the males and females' ratio did not differ from unity in a population of Western Australia (N = 325), but in a population of Pacific Australia more males than females predominated significantly (N = 206). Something similar happened also happens with the species Isostichopus fuscus in two populations of Mexico (Pañola-Madrigal et al, 2017). Another species of the same genus (Holothuria tubulosa) was studied in the Aegean Sea (N = 166) by Kazanidis et al (2010) and in the Adriatric sea (N = 130) by Despalatović et al (2004), both obtained the same result (1:1) regarding the sex ratio.…”

“…Despite the fact that the sex ratio is 1:1 in most holothurians (Ramofafia, Byrne & Battangle, 2001;Asha & Muthiga, 2008;Fajardo-León et al, 2008;Kazanidis et al, 2010; Peters-Didier, Pardo, Garrido & Gallardo, 2018;Cahuzac et al, 2019), as in the Ría de Vigo, some species demonstrated an unbalanced ratio (Costelloe, 1985;Navarro et al, 2012;Omar, Abdel Razek, Abdel Rahman & El Shimy, 2013;Pañola-Madrigal, Calderón-Aguilera, Aguilar-Cruz, Reyes-Bonilla & Herrero-Pérezrul, 2017). In fact, Santos et al (2016) found in H. forskali, more female than males; these authors explain that the place of sampling is subject to strong tides which is considered to be another major factor affecting the balanced sex ratio due to the fact that strong sea waves often promote species´ evisceration as a stress response.…”

“…Correlation of reproductive cycle with conditions existing in the natural environment has been examined for a number of sea cucumbers (Costelloe, 1985;Sewell & Bergquist, 1990;Hamel, Himmelman & Dufresne, 1993;Hopper, Hunter & Richmond, 1998;Asha & Muthiga, 2008;Pañola-Madrigal et al, 2017) since, the reproductive activities of echinoderms are regulated by endogenous factors, which, in turn, are affected by exogenous environmental factors (Costelloe, 1985). According to Costelloe (1985), the environmental stimuli that have the most influence on sexual cycles directly or indirectly are: changing temperature, salinity, photoperiod, food and habitat availability and juvenile recruitment and survival.…”

“…The reproduction pattern of this species is contrary to that the other holothurians, which reproduce during the warmer months when the days are longer. In this way the larvae have greater food availability due to the proliferation of phytoplankton (Cameron & Fankboner, 1986;Sewell & Bergquist, 1990;Conand, 1993;Hamel et al, 1993;Morgan, 2000;Ramofafia et al, 2001;Guzmán et al, 2003;Despalatović et al, 2004;Kazanidis et al, 2010;Omar et al, 2013;Pañola-Madrigal et al, 2017). The spawning period of H. forskali takes place when the temperatures are lower as well as are the species Holothuria whitmaei (Shiell & Uthicke, 2006), Aslia lefevrei (Costelloe, 1985) or Holothuria nobilis (Conand, 1993).…”