Female maturation, egg characteristics and fatty acids profile in the seahorse Hippocampus guttulatus

Knowledge of the biology and ecology of seahorses (Hippocampus spp.) is scarce, but has been increasing in recent years due to their conservation status. Captivity breeding programmescan be a valuable source of information on the reproductive biology of seahorses.A captive broodstock of Hippocampus guttulatus Cuvier 1829 was established in 2006 and kept under natural-like photoperiod and temperature. Female maturation was studied during the whole reproductive season in 2007. Most egg clutches were released from May (17 ◦C; 15L:9D) to October (18 ◦C; 13L:11D), with peak releases occurring in June–August (20 ◦C; 16L:8D–14L:10D). Throughout the study, four egg morphotypes were found;tworegression equations were proposed for estimating egg/yolk volume based on measurements of egg and yolk biometrics. Female weight was positively correlated with yolk volume/egg volume ratio (Yv/Ev) (rs = 0.523, n = 21, P < 0.05) but not with Ev or Yv. Egg dry weight (567±141 g) was correlated with Yv (rs = 0.384, n = 31, P < 0.05).Meanclutch size and clutch biomass were 242±142 eggs and 137±87mg dry weight, respectively. Clutch size was positively correlated to female weight (rs = 0.479, n = 25, P < 0.05). Inter-clutch intervals (days) were affected by temperature (◦C) as described by the following equation: Interval = 357.55e−0.1283 Temp. Estimated inter-clutch intervals at 16, 18 and 20 ◦C were 45.9, 35.5 and 27.5 days, respectively. Egg total lipids accounted for 31.9±3.1% dry weight. Absolute lipid content in eggs was correlated with egg dry weight (rs = 0.907, n = 41, P < 0.001) and Yv (rs = 0.384, n = 41, P < 0.5). In decreasing order of relative percentage, the most important fatty acids, were 18:1n9, 16:0, 18:2n6, 20:5n3, 18:0 and 22:6n-3. The level of n-3 HUFA was 18.5±0.7% (38.4±3.3 mg/g dry weight). The profile of fatty acids in eggs resembled that displayed by the broodstock diet (enriched adult Artemia).

The study was financed by the Spanish Ministry of Science and Technology (CGL2005-05927-C03-01), as part of a coordinated research project (Proyecto Hippocampus; 2005/PC091). Funding was also partially provided by the Regional Government of Galicia (Xunta de Galicia; PGIDIT06PXIC402106PN). P. Quintas was supported by a postdoctoral I3P contract (JAE Doc) from the Spanish Council for Scientific Research (CSIC). C. Silva was granted by EU (Erasmus 29154-IC-1-2007-1-PT-ERASMUS-EUC-1). We thank to Xunta de Galicia for providing permission in the study and capture of wild seahorses. We also thank A.Vilar, M. Castelo and M. Moyano (Aquarium Finisterrae, A Coru˜ na), and Dr. J. Pintado (IIM, CSIC) for helping with the capture of wild seahorses, and Dr. Ricardo Calado, Dr. Ierecê Rosa and Dr. Ike Olivotto for the review and comments on the manuscript.

Peer reviewed