Single nucleotide polymorphisms are suitable for assessing the success of restocking efforts of the European lobster (Homarus gammarus, L.)

The European lobster (Homarus gammarus) forms the base of an important fishery along the coasts of Europe. However, stocks have been in decline for many years, prompting new regulations in the fishery and also restocking efforts. An important feature of any restocking effort is the assessment of success in the number of released juveniles that stay and become adult over time. Here, we tested the power of a single nucleotide polymorphism (SNP) DNA marker panel developed for population assignment to correctly infer parentage on the maternal side of lobster larvae, in the absence of known fathers, using lobsters included in a current restocking effort on the Swedish west coast. We also examined the power to reconstruct the unknown paternal genotypes, and examined the number of fathers for each larval clutch. We found that the 96-SNP panel, despite only containing 78 informative markers, allowed us to assign all larvae to the correct mother. Furthermore, with ten genotyped larvae or more, confident paternal genotypes could be reconstructed. We also found that 15 out of 17 clutches were full siblings, whereas two clutches had two fathers. To our knowledge, this is the first time a SNP panel of this size has been used to assess parentage in a crustacean restocking effort. Our conclusion is that the panel works well, and that it could be an important tool for the assessment of restocking success of H. gammarus in the future.

A Method of Solubilizing and Concentrating Astaxanthin and Other Carotenoids

The valuable marine carotenoid, astaxanthin, is used in supplements, medicines and cosmetics. In this study, crustacyanin, an astaxanthin-binding protein, was used to solubilize and concentrate astaxanthin. The recombinant crustacyanin of European lobster spontaneously formed an inclusion body when it was over-expressed in Escherichia coli. In this study, fusing the NusA-tag to the crustacyanin subunits made it possible to express in a soluble fraction and solubilize astaxanthin in aqueous solution. By cutting off the NusA-tag, the crustacyanin subunits generated the pure insoluble form, and captured and concentrated astaxanthin. Overall, the attaching and releasing NusA-tag method has the potential to supply solubilized carotenoids in aqueous solution and concentrated carotenoids, respectively.

Single Nucleotide Polymorphisms Are Suitable For Assessing The Success of Restocking Efforts of The European Lobster (Homarus Gammarus, L.)

The European lobster (Homarus gammarus) forms the base of an important fishery along the coasts of Europe. However, stocks have been in decline for many years, prompting new regulations in the fishery and also restocking efforts. An important feature of any restocking effort is the assessment of success in the number of released juveniles that stay and become adult over time. Here, we tested the power of a SNP DNA marker panel developed for population assignment to correctly infer parentage on the maternal side of lobster larvae, in the absence of known fathers, using lobsters included in a current restocking effort on the Swedish west coast. We also examined the power to reconstruct the unknown paternal genotypes, and examined the number of fathers for each larval clutch. We found that the 96-SNP panel, despite only containing 78 informative markers, allowed us to assign all larvae to the correct mother. Furthermore, with 10 genotyped larvae or more, confident paternal genotypes could be reconstructed. We also found that 15 out of 17 clutches were full siblings, whereas two clutches had two fathers. To our knowledge, this is the first time a SNP panel of this size has been used to assess parentage in a crustacean restocking effort. Our conclusion is that the panel works well, and that it could be an important tool for the assessment of restocking success of H. gammarus in the future.

Population Characteristics of the European Lobster, Homarus gammarus in the Adriatic Sea: Implications for Sustainable Fisheries Management

The European lobster, Homarus gammarus, was sampled from September 2016 to August 2017, using pots and gillnets in the Eastern Adriatic Sea. Official landings were also analyzed (2008–2020). The majority of landings were from the Northern Adriatic and showed an increase of 18.5% over the study period. Results revealed an extremely low catch rate that fluctuated significantly by season. Dominance by specimens in the size classes of 90–110 mm carapace length (CL) was observed. Experimental design revealed spatial heterogeneity, with larger individuals caught further from the coast (>3 nm) and undersized specimens caught near the coast (<3 nm). With increasing CL and total length (TL), an increase in weight was higher in males than females. TL and abdomen width (AW) increased linearly with CL and were more pronounced in females. At 80 mm CL, females started to develop secondary sex characteristics with wider AW than males. The results suggest that the modern legal framework is appropriate for lobster fisheries and a longer fishing season is not advisable, despite a positive catch trend in the northern part of the sea. Additional efforts are desirable to reduce fishing pressure in the coastal part. The morphometric relationships could reveal population characteristics required as inputs in stock assessment analysis for effective management.

Replacement of Antarctic krill (Euphausia superba) by extruded feeds with different proximate compositions: effects on growth, nutritional condition and digestive capacity of juvenile European lobsters (Homarus gammarus, L.)

Extruded feeds are widely used for major aquatic animal production, particularly for finfish. However, the transition from fresh/frozen to extruded/pelleted feeds remains a major obstacle to progressing sustainable farming of European lobster (Homarus gammarus). The aim of the present study was to investigate the effects of using extruded feeds with different protein levels and lipid/carbohydrate ratios on growth, feed utilisation, nucleic acid derived indices (sRD) and digestive enzymatic activity of H. gammarus juveniles. Six extruded feeds were formulated to contain two protein levels (400 and 500 g/kg), with three lipid/carbohydrate ratios (LOW – 1:3; MEDium – 1:2; HIGH – 1:1). The extruded feeds were tested against Antarctic krill (Euphausia superba) used as control (CTRL). Overall, the CTRL and 500MED feed supported the highest growth and nutritional condition estimated by means of sRD, while the poorest results were observed for the 400HIGH and 400MED groups. The FCR was significantly lower in the CTRL than all extruded feeds, among which the most efficient, i.e., lower FCR, was the 500MED. The highest activity of trypsin and amylase in lobsters fed the 400MED and 400HIGH feeds points to the activation of a mechanism to maximise nutrients assimilation. The highest lipase activity observed for the 500LOW and 500MED groups indicates a higher capacity to metabolise and store lipids. Overall, the results suggest that the 500MED feed (500 g/kg protein, 237 g/kg carbohydrates and 119 g/kg lipids) is a suitable extruded feed candidate to replace Antarctic krill, commonly used to grow lobster juveniles.