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Rearing of the seahorse Hippocampus guttulatus: Key factors involved in growth and survival

Autor Blanco, Andreu
DirectorPlanas, Miguel
Fecha de publicación 2014
ResumenSeahorse wild populations are worldwide threatened by habitat loss, incidental bycatch and direct fishing pressure either for Traditional Chinese Medicine, aquarium trade or curios. Resilience variability of seahorses to population declines resulted in the inclusion of all seahorse species in the Red List of Endangered Species of the IUCN in 1996. Furthermore, all species were also included in 2002 in Appendix II of The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Population declines require the application of conservation management measures such as captive-breeding for recovery of wild populations, a potential solution to guarantee wild population welfare. Successful seahorse aquaculture operations should develop low-technology protocols for seahorse rearing while providing a commercially viable trade ensuring conservation goals and offering alternative livelihood to wild-seahorse fishers. The present Thesis is focused on the European long-snouted seahorse Hippocampus guttulatus, whose wild populations in the Galician coast are genetically under a long-term demographical reduction. The knowledge on husbandry and rearing of H. guttulatus in captivity were firstly initiated by Proyecto Hippocampus establishing a breeding protocol for adult seahorses and the base of knowledge for the rearing of juveniles Breeding improvements with the addition of live shrimp (Palaemonetes varians) and mysidaceans (Leptomysis sp. and Siriella sp.) as diet supplement, and the establishment of breeding techniques for the artificial manipulation of the captive conditions resulted in the enhancement of mating events and breeding all year around, the production of high quality newborn and a huge reduction (from > 95% to 6%) in the presence of abnormal or immature newborn in captive breeding. After the establishment of adequate breeding conditions, the following step in the production of seahorse juveniles was the development of a successful rearing technique, which was the main objective of the present Thesis.
The initial limited knowledge on the rearing of juveniles resulted in low survivals and massive mortality events that difficulted deciphering the essential changes needed to achieve a reliable rearing technique. In the present Thesis, significant improvements were achieved by enhancing the rearing technique thorough the study at different levels: including zootechnics (aquaria design), physical factors (aeration intensity, photoperiod and temperature) and feeding (prey preference, prey type/size and digestion capabilities). The first step in the early larval rearing of fish is the establishment of an adequate rearing system in which the aquaria design results essential for seahorses. The design of satisfactory aquaria, ensuring an even distribution of prey and juvenile in the water column, and the assessment of aeration/water turbulence levels were found to be of great importance to avoid both the access of juveniles to water surface and the presence of stagnant volumes in the aquaria. Under optimal conditions, the appearance of water surface overcrowding, swim bladder dysfunctions and accidental ingestion of air bubbles must be reduced as much as possible to reduce undesired mortalities. Accordingly, the studies performed in this Thesis in which three different aquaria designs (rectangular, spherical and pseudoKreisel) and two different aeration intensities (weak and strong) were assayed. Significant improvements in rearing performances were reached when pseudoKreisel aquaria and strong aeration levels were used. Average survivals in 30 days after release (DAR) juveniles fed on Artemia and copepods increased from 16-22% in rectangular and spherical aquaria to 69% in pseudoKreisel aquaria. Additonally, juveniles fed on Artemia showed a 3-folds increase in survival under strong aeration levels with respect to those under weak aeration levels (41 and 13%, respectively). However, no significant differences were found for aeration levels when seahorse juveniles were fed on diets supplemented with copepods.
Despite water circulation and turbulence in the aquaria, the positive phototaxis of juvenile seahorses could result in swimming to water surface. The lateral incidence of light of and the darkening of the upper part of the aquarium walls reduced brightness in water surface and walls and resulted essential if compared to previous results. As seahorses are visual predators, it was hypothesised that an extended photoperiod (24h continuous light) together with the continuous availability of prey would increase growth and survival rates. However, the application of an extended light regime did not affect the rearing performance of seahorses when compared to a day-night photoperiod regime (16h Light :8h Dark). Among physical factors potentially involved in the rearing success, temperature is one of the most important. Three temperature levels (15, 18 and 21°C) within the range of water surface temperatures registered annually in the Galician coast were studied. Growth and survival resulted in suboptimal development of 30 DAR juveniles when reared at 15°C, a temperature which is not far from T0 (Threshold temperature at which growth is arrested). Conversely, high performances were achieved at 18ºC and 21ºC both for growth (8% and 11%, respectively) and survival (86% and 81%, respectively). In that study, it was demonstrate for the first time the suitability of effective day degrees (Do eff) as a temperatureindependent scale to quantify growth in fed juveniles and growth models were obtained for temperatures ranging from 14 to 26ºC.
Feeding and nutritional requirements have been considered a main bottleneck in the culture of seahorses. The early rearing of seahorses has traditionally relied on the supply of Artemia sp. and rotifers as first prey. However, copepods alone or supplemented with Artemia improved the rearing of seahorse juveniles. In order to ascertain ontogenetic feeding preferences in juveniles, three different preys (rotifer, Artemia nauplii and adult/copepodite Acartia tonsa) were tested. Rotifers were systematically rejected at all developmental stages, implying that is not a suitable prey for this seahorse species. Conversely, copepods and Artemia nauplii were actively captured since newborn release. However, the former were preferred over Artemia nauplii from 3 to 15 DAR, whereas the later were preferentially selected afterwards. The results on prey selection and mouth growth showed that juveniles would be able to ingest prey much bigger than those provided in our study (168 – 978 in length and 85 - 322μm in width), especially after 15 DAR. The presence of undigested and alive Artemia nauplii in feces from very young juveniles was accompanied by low growth rates, high mortalities and weakness of juveniles. This finding could be at least partially explained by the low chitinase activity recorded in the juveniles. On the contrary, copepods were efficiently digested. Digestive enzymatic activities recorded were very low, independently of the diet supplied (Artemia alone or supplemented with copepods). However, the activities increased in more developmental stages when copepods were included in the diet during the first days. Accordingly, a successful diet scheme for young H. guttulatus juveniles should include copepods during the first days for a better performance, especially if copepods are offered as the sole prey for at least the first 5 days after male’s pouch release (G= 10% and 76% survival). The results arisen from the present Thesis have allowed the development of a procedure for the early rearing of the seahorse Hippocampus guttulatus. The procedure is based on the use of pseudoKreisel aquaria, strong aeration (and an appropriate water inlet placement) and a temperature of about 19ºC under a 16L:8D photoperiod regime. The feeding scheme of that rearing methodology includes the use of copepods from 0 to 5 DAR, copepods + Artemia nauplii form 6 to 10 DAR and Artemia nauplii/metanauplii from 11 to 30 DAR. By the application of such a protocol the life cycle of Hippocampus guttulatus was closed after obtaining F2 juvenile batches. The availability of that methodology also permitted the introduction of Hippocampus guttulatus in the aquarium trade (high economical value) with stable production of juveniles, which is a need for future actions directed towards the reinforcement of wild populations
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URI http://hdl.handle.net/10261/98500
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