The Ph.D. thesis of María Fernández focused on these two potentially important species for aquaculture
The search for new cultivable species is essential for the development of aquaculture in Galicia, but it is also a tool to protect certain types of fish that are subject to an overfishing situation. Among the alternatives for this diversification of aquaculture are hake or cod, species that are at different levels of development and in which the researcher of the ReXenMar laboratory of the Marine Research Center of the University of Vigo María Fernández Míguez focused her doctoral thesis.
The thesis, supervised by Associate Professor Pablo Presa (ReXenMar) and researcher Montse Pérez, from the AquaCOV group of the Spanish Institute of Oceanography (IEO-CSIC), aims to develop and apply genetic tools as a methodological strategy to enhance the optimization of the stocks Of these two fishing species. To this end, she focused on gene sequencing and molecular phylogenetics, gene expression analysis and the development of EST markers, respectively to resolve situations of phylogenetic uncertainty, the selection of progenitors in culture and the characterization of fishery stocks.
New species, new challenges
Diversification of aquaculture species involves challenges during early stages of life, such as low survival or malformations, many of them due to ignorance in the management of these new species. In the case of Atlantic cod (Gadus morhua), explains María Fernández Míguez, “its reproductive cycle is closed and there are several companies that have adult and egg production programs for marketing, such as the Norwegian Nofima through the Cod breeding program , funded by the Norwegian Ministry. As for hake (Merluccius merluccius), the reduction in the sustainability of fisheries after decades of over-exploitation and the health and commercial impact of the Anisakis infestation has made it attractive to start domesticating this species.” The first spontaneous spawning in captivity was achieved in 2009 at the IEO facilities in Vigo, where two spawning stocks were maintained until 2016. A constant spawning activity made possible the description of the embryonic development of the species (Sánchez et al., 2012) and the development of specific diets for larval feeding (Nande et al., 2017).
In her dissertation, Fernández Míguez she developed and applied genetic tools as a strategy to optimize the stocks of both species. Thus, with regard to hake, their purpose is to better understand its genetics and reduce its over-exploitation. To this end, she focused on the phylogenetic analysis, ie the genetic kinship, of all the described hake species, as well as the clarification of the presence of synonymous species or morphotypes, ie the morphological variants of the same species. Another objective was to analyze the impact of overfishing on the population size of European hake to prevent the loss of adaptation to change in the environment, for example, a rise in temperature due to climate change, using samples from the Historical Fisheries Records of the Oceanographic Institute of Vigo (1975-2014). Her research also addressed the origin of differences between Atlantic and Mediterranean populations of European hake with genetic markers, while focusing on expanding knowledge about the influence of maternal factors on the quality of Atlantic cod eggs at Nofima in the Norwegian city of Tromsø and the Oceanographic Institute of Vigo. The researcher explains that advances in the cultivation of this species, close to hake, allow us to know the factors that make an egg of “good quality” and, therefore, obtain higher survival rates during cultivation.
Both species still show high mortalites in the primary stages making the cost greater than the benefit. That is why several research groups are focused on improving the quality of the egg and the survival of the larvae as well as the selection of the breeders that give better spawning.
Conclusions
Regarding the conclusions of her research, Fernández Míguez details that regarding the phylogenetic advances in the genus Merluccius, the phylogenetic trees obtained indicate that Merluccius angustimanus(northern Gulf of California) may have resulted from hybridization between M. productus and M. gayi. about 0.25 million years ago. They also indicated that the five rare South Pacific morphotypes would have a hybrid origin between M. australis and M. gayi. Therefore, no new fishery can be defined or claimed based solely on rare morphotypes.
With regard to structural scenarios in European hake fisheries, different types of genetic markers were used for different goals, ie directional markers to identify remaining selection patterns and episodes of extreme drift, balanced markers to determine current evolutionary novelty and adaptive potential for fishery sustainability, and neutral markers to analyze demographic dynamics of genetic relevance for fisheries management.
In the chapter focusing on the effective genetic size of the southern hake population, the researcher explains that “the southern stock is made up of a single genetic stock that was eroded with a maximum of overexploitation in 1991-1995. The beginning of the recovery of the stock after 2005 was probably reinforced by EU fisheries policies, but also by the migration between fisheries that had already been discovered by this research team in 2011. However, this recovery is not expected to be complete after episodes. of sustained overfishing. The assessment based solely on demographic models seriously underestimates the genetic erosion that operates on the reproductive potential of the stock. The incorporation of different data sources and genetic controls would lead to a more realistic biological assessment and may allow the risk of extinction to be assessed through genetic factors.
Finally, regarding the early genetic expression and quality of Atlantic cod eggs, Fernández Míguez found that there is a differential expression between the stages of development of Atlantic cod, with the transition from maternal transcription to zygotic being essential. Variation in gene expression was also observed during the spawning season (it occurs during spring and several spawnings can be obtained that vary in quality). Therefore, the laying period must be taken into account to reduce production costs by choosing the highest quality periods. This study suggests that knowledge of the molecular basis of egg quality is a line of applied research of utmost relevance to the aquaculture sector.
Applications
These results will help move forward in different areas. Thus, the knowledge of existing hake species and the presence of morphotypes can be used in relation to commercial fraud, i.e. in the sale of proximal species, as well as the adjustment of the fishing legislation for each species. Secondly, the knowledge of the composition of the hake stocks allows to protect the species from overfishing, adjusting the quotas taking into account the recovery of the species based on the historical data registered in the Oceanographic Institute of Vigo. On the other hand, the knowledge of the factors that are affecting the quality of cod and hake eggs, opens the door to obtaining more efficient cultures and thus reduce their costs.
Source: DUVI