Step by step optimization of a sperm cryopreservation protocol for spotted wolffish (Anarhichas minor Olafsen, 1772)

High protein requirements of juvenile Atlantic wolffish, Anarhichas lupus: Effects of dietary protein levels on growth, health, and welfare

The objective of the present study was to investigate the optimal dietary protein requirement and the effect of varying protein levels on the growth and health of juvenile, wild-caught Atlantic wolffish, Anarhichas lupus, a promising candidate for cold-water aquaculture diversification. Six iso-energetic (ca. 18.3 MJ kg-1), fish meal-based experimental diets were formulated with crude protein levels ranging from 35% to 60%, with graded increments of 5% in a 12-week feeding trial in a recirculating aquaculture system (RAS). Weight gain, specific growth rate (SGR), and condition factor (K) were evaluated in response to dietary protein levels. Liver, muscle, and blood parameters were assessed for possible changes in protein and lipid metabolism and welfare. Overall growth was highly variable throughout the experiment on all diets, as expected for a wild population. The feed with highest in protein (60%) inclusion resulted in the highest growth rates, with an average weight gain of 37.4% ± 33.8% and an SGR of 0.31% ± 0.2% day-1. This was closely followed by feeds with 55% and 50% protein inclusion with an average weight gain of 22.9% ± 34.8% and 28.5% ± 38.3%, respectively, and an SGR of 0.18% ± 0.3% day-1 and 0.22% ± 0.3% day-1, respectively. Fish fed the high protein diets generally had increased hepatic lipid deposition (17%-18%) and reduced free fatty acid levels (3.1-6.8 μmol L-1) in the plasma relative to fish that were fed the lower protein diets (35%-45%). No effects of diet were found on plasma protein levels or muscle protein content. Furthermore, stress parameters such as plasma cortisol and glucose levels were unaffected by diet, as were plasma ghrelin levels. Overall, these results suggest that a high protein inclusion in the diet for Atlantic wolffish is required to sustain growth with a minimum protein level of 50%.

Effect of cryopreservation on post-thaw motility and viability of Grey mullet, Mugil cephalus sperm (Linnaeus, 1758)

In this study, we optimized a simple method of cryopreservation for Mugil cephalus sperm based on post-thaw motility and viability. A series of experiments were conducted by changing the extender, cryoprotectant and freezing height above the liquid nitrogen (LN) surface. First, we carried out the cryopreservation using the extender V2E and cryoprotective agents (CPAs) namely, propylene glycol (PG), methanol (MeOH), glycerol (GLY), ethylene glycol (EG), dimethylsulfoxide (Me2SO) and dimethylacetamide (DMA) at a final concentration of 5% and 10%. We found that 10% of GLY, EG and Me2SO were more suitable compared to other CPAs. Then, different freezing heights (6, 8, 10 and 12 cm) above the LN surface were experimented with extender V2E and optimized CPAs. Then, 0.3 M of glucose, sucrose and trehalose were tested as extender along with optimized CPAs and freezing height. Additionally, the effect of fast-rate freezing and storage days (7, 30 and 180) on post-thaw sperm quality was documented using the factors optimized in earlier experiments. For all experiments, the fresh sperm was diluted at a ratio of 1:1 with cryomedium (CPA + extender), loaded into cryovials (2.0 mL) and frozen. The cryopreserved sperm was thawed at 30 °C for 90-120 s and their quality was evaluated. Among the experimented factors, sperm diluted in cryomedium (0.3 M glucose + 10% EG) and frozen at 4 cm above the LN surface registered significantly (P < 0.05) highest post-thaw motility (73 ± 2%) and (71 ± 1%) viability. Fast-rate freezing has resulted in lower (about 30%) post-thaw motility and viability of sperm. The storage days (7, 30 and 180) did not have a significant effect on post-thaw sperm quality. Overall results show that using the factors optimized through this study, high-quality sperm can be obtained after cryopreservation.

Optimization of Sperm Cryopreservation Formulation in Portunus trituberculatus

Portunus trituberculatus is a very important marine economic species, and its aquaculture industry has been developing rapidly. However, the phenomenon of marine wild capture of P. trituberculatus and germplasm degradation has become increasingly serious. It is necessary to develop the artificial farming industry and carry out germplasm resource protection, for which sperm cryopreservation technology is an effective method. This research compared three methods (mesh-rubbing, trypsin digestion, and mechanical grinding) for acquiring free sperm, and the best method was mesh-rubbing. Then, the optimal cryopreservation conditions were selected, and the optimal formulation was sterile calcium-free artificial seawater, the optimal cryoprotectant was 20% glycerol, and the best equilibrium time was 15 min at 4 °C. The optimal cooling program was suspending the straws at 3.5 cm on the liquid nitrogen surface for 5 min and then storing them in liquid nitrogen. Finally, the sperm were thawed at 42 °C. However, the expression of sperm-related genes and the total enzymatic activities of frozen sperm were significantly decreased (p < 0.05), which showed that sperm cryopreservation damaged the sperm. Our study improves the sperm cryopreservation technology and the yield of aquaculture in P. trituberculatus. Additionally, the study provides a certain technical basis for the establishment of a sperm cryopreservation library of crustaceans.

Spotted Wolffish Broodstock Management and Egg Production: Retrospective, Current Status, and Research Priorities

The first artificially fertilized spotted wolffish (Anarhichas minor) eggs hatched in Norway in the mid-1990s as this species was considered by Norwegian authorities to be a top candidate species for cold-water aquaculture in the North Atlantic regions. Previous research conducted in Norway (since 1992) and Canada (since 2000), focused on identifying key biological parameters for spotted wolffish cultivation which led, respectively, to the rapid establishment of a full commercial production line in northern Norway, while Québec (Canada) is witnessing its first privately driven initiative to establish commercial production of spotted wolffish on its territory. The control of reproduction can be viewed as a major requirement to achieve the development of performant strains using genetic selection tools and/or all-year-round production to bring about maximal productivity and synchronization among a given captive population. Although the basic reproduction aspects are more understood and controlled there are still some challenges remaining involving broodstock and upscaling of operations that limit the achievement of a standardized production at the commercial level. Quality of gametes is still considered a major constraint and it can be affected by multiple factors including nutrition, environmental conditions, handling practices, and welfare status. Internal insemination/fertilization and the protracted incubation period are challenging as well as the establishment of a health monitoring program to secure large-scale operations. The profound progress achieved in the control of reproduction, sperm handling, and cryopreservation methods for this species is presented and discussed. In this review, we also go into detail over the full range of up-to-date cultivation practices involving broodstock and identify areas that could benefit from additional research efforts (i.e., broodstock nutrition, health and welfare, scaling-up egg and larval production, genetics, and development of selective breeding programs).

Spotted wolffish (Anarhichas minor) sperm cryopreservation in 5-mL cryovials

In spotted wolffish Anarhichas minor aquaculture, cryopreservation is used to secure sperm availability throughout the entire spawning season. Under current protocols, sperm is cryopreserved in 0.5-mL straws. This implies thawing a considerable number of straws for insemination with cryopreserved sperm. In this work, we scale up the spotted wolffish sperm cryopreservation procedure through the development of a protocol for sperm cryopreservation in 5-mL cryovials. Different freezing (distances from the liquid nitrogen surface) and thawing rates were tested. The best results were obtained with cryovials frozen at a distance of 1.5 cm from the liquid nitrogen surface and thawed either at 15 or 10 °C for 4 and 6 min, respectively. Under these conditions, similar percentage of motile cells, sperm velocity and percentage of viable cells were obtained in comparison with the sperm cryopreserved in the traditional 0.5-mL straws. This protocol will facilitate the process of insemination with cryopreserved sperm in the spotted wolffish hatcheries.

The effects of extenders, cryoprotectants and conditions in two-step cooling method on Varicorhinus barbatulus sperm

In this study, we developed an optimal cryopreservation procedure for Varicorhinus barbatulus sperm. To this end, we optimized (1) the types and dilution ratios of extenders; (2) types and final concentration of cryoprotectants; and (3) freezing conditions, including equilibration time, height above the surface of liquid nitrogen (LN), and the cooling times in the two-step cooling method. The optimum result was obtained when the sperm was diluted at a 1:9 ratio in D-17 with 10% methanol, equilibrated at 4 °C for 10 min, held at 7 cm above LN for 2 min, and finally stored in LN. After storage for 12 h in LN, the sperm was thawed in a water bath at 40 °C for 6s, the post-thaw sperm motility was 66.10 ± 7.12%, while the corresponding rate for fresh sperm was 87.08 ± 2.38%. Using computer-assisted sperm analysis, we found a significant decrease in the motility parameters of post-thaw sperm, especially the parameters related to velocity. To evaluate the effects of cryopreservation on the structural integrity of sperm, transmission electron microscopy and scanning electron microscopy were employed, which showed the defects in frozen sperm, including: abnormal heads, damaged plasma membranes, broken tails, and the disappearance of the mitochondrial internal crest. In addition, we determined the mitochondrial membrane potential to assess the functional integrity of frozen sperm. Our results showed a decrease in the mitochondrial function of frozen sperm. This procedure could be used alongside cryopreservation of V. barbatulus and supports its commercial-scale production and species conservation.