The lack of an adequate diet for the first days of life; the need for standardization of culture techniques and the limited knowledge that is available about this phase of life in the marine environment are the main causes of the failure in the commercial cultivation of the species commonly known as rock octopus and scientifically as Octopus vulgaris. For many years, researchers from all over the world have been dedicated to studying the aquaculture of this species, which due to its biological and physiological characteristics is an ideal candidate for cultivation as it presents very rapid growth, great fecundity and very good adaptation to captivity. However, the aquaculture of this species continues to be limited by the high mortality in the first days of life, a period in which the paralarva presents mortalities of up to 99% in the first month.
If the Octophys project was the first to focus on the metabolic needs of this species, leading to the creation of an enrichment protocol that allowed for improved growth of the paralarva, the study of the culture is currently continuing with the Octowelf project, focused on the well-being and health in the early stages of the life of the common octopus, the effect of nutrition and environmental factors. The universities of Vigo, Granada and La Laguna; the IEO of Vigo and Tenerife and the CSIC of Vigo are participating in this project, which includes the study on the feasibility of using the color of the digestive gland of paralarvae as an indicator of exogenous feeding during the first days of life, developed by researcher Raquel Fernández Gago. This work, which is part of the doctoral thesis, which Raquel Fernández carried out under the direction of Francisco Rocha, professor and researcher at the Department of Ecology and Animal Biology at the University of Vigo, was developed in collaboration with the Norwegian Marine Research Institute Havforskningsinstituttet.
Use of nutritional or condition indices
“Current studies focus on determining the sources of stress in the culture and the genes that are expressed during it, as well as indices of condition or nutrition”, explains the researcher, who recently detailed her work in one of the days of the Café con Sal cycle, which takes place at the Ecimat. Raquel Fernández recalls that during the first days of life the paralarvae must learn to eat, so feeding becomes one of the most important factors within the culture that can trigger stress. In the natural environment, the paralarvae feed on larvae of Charidea and Brachiura, but in the culture, given the impossibility of being fed with these species, Artemia sp is supplied, which does not provide all the nutritional needs of the paralarvae, resulting in high mortality rates in the culture.
“The use of nutritional or condition indices is based on the fact that during periods of starvation, some organs, including some glands, are more sensitive and undergo modifications in short periods of time, modifications that allow the establishment of nutritional indices that will determine the health status of the animals,” explains the researcher, who points out that currently the most used indices in cephalopods are based on morphometric measurements, determination of dry weight, total length or digestive enzymes, which although they provide a lot of information, involve the total destruction of the animal.
A non-destructive and easy-to-apply method
The study carried out by Raquel Fernández proposes the digestive gland of paralarvae as an ideal indicator of nutritional status “because it is easy to see through the transparent mantle” and many authors have shown that this organ undergoes histological modifications during the digestion process. To carry out the research, several strips of eggs were collected from the Ría de Vigo, corresponding to a natural spawning, leaving the rest to allow it to continue contributing to the natural recruitment of the species. After the eggs hatched, which were taken to the Ecimat, the culture was carried out, in which the nutritional conditions of the animals were measured daily, observing the changes present in the digestive gland, for which they were photographed after being anesthetized to reduce their stress. “This non-destructive method allows us to observe changes that are easily noticeable in the digestive gland after the animal accepts the food, changes that will be quantified after measuring the different areas of color present in the digestive glands,” explains the researcher, who points out that the use of this technique has allowed us to relate the modifications of this gland to the nutritional status, “which represents a great advance in determining the nutritional status of octopus paralarvae in their culture.”
Source: duvi
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