Unidirectional hybridization between American paddlefish Polyodon spathula (Walbaum, 1792) and sterlet Acipenser ruthenus (Linnaeus, 1758).

Interspecific hybridizations among sturgeon species are feasible and often bidirectional. The American paddlefish (Polyodon spathula) from Family Polyodontidae and sturgeon species from Family Acipenseridae were reported capable of hybridization, but viable hybrids have been described only in crosses with the American paddlefish as paternal parents. In the reciprocal cross, the hybrids were not viable however embryos start to develop and reach late gastrula and early neurula stages. The goal of this study was to examine the hybridization between the sterlet sturgeon (Acipenser ruthenus) and the American paddlefish. Hybrid and purebred crosses were produced by artificial fertilization. Viable hybrid offspring were harvested (three month old) and verified in the families produced by female sterlet crossing with male American paddlefish. In the reciprocal hybrid crosses with female American paddlefish and male sterlet, the embryos development did not pass over 120 h post fertilization, indicating the unidirectional hybridization between American paddlefish and sterlet. Chromosome counting showed for the same ploidy level of viable hybrid and parent species. Analysis of three microsatellite markers confirmed the unidirectional hybridization between the American paddlefish and the sterlet species. Overall, the inferred genetic cause suggests that unidirectional hybridization between American paddlefish and sterlet may be the case not only for these two species but likely also between American paddlefish and other sturgeon species.

Evaluation of Post-Larval Diets for Indoor Weaned Largemouth Bass (Micropterus salmoides).

This study aimed to evaluate different commercial diets (Otohime C1, Aller Futura (AF), Biomar Inicio Plus (BIP)) and one experimental feed (EF) in terms of their effectiveness as post-larval diets for indoor weaned largemouth bass, LMB (Micropterus salmoides). Key variations in the content of nutritive values were monounsaturated fatty acid (MUFA) and highly unsaturated FA (HUFA) ω3. Fish were fed with one of four tested diets from the 33rd to the 40th day post-hatch (DPH). Biometric indices, digestive enzyme-specific activities, thyroid hormone status, and mRNA expression of genes coding for skeleton, neuron, and muscle growth were analyzed. The lowest skeletal deformity rate and highest survival among the treatments were seen in BIP-fed fish. Dietary lipids, with an appropriate balance between MUFA and polyunsaturated FA (PUFA), alongside amino acid balance, were shown to be the main contributors to the growth of the skeleton and/or fish survival. On the other hand, fish growth is correlated with fish digestive capacity and feed moisture percent rather than feed quality. Unexpectedly, BIP-fed fish were attributed with the lowest expression of skeleton differentiation markers, which may reflect the sacrifice of scale and/or cranium growth at the expense of somatic growth. This study highlights the role of non-marine ingredients in the nutrition of post-larval LMB.

Nursing of Pike-Perch (Sander lucioperca) in Recirculating Aquaculture System (RAS) Provides Growth Advantage in Juvenile Growth Phase.

This study aimed to estimate the efficacy of two pike-perch juvenile production technologies: exclusive Recirculating Aquaculture System (RAS) culture (the RAS group) and pond larviculture with a transfer to the RAS at the 42nd day post-hatch (DPH). Both direct weaning on dry feed (the Pond-D group) and 10-day gradual weaning using bloodworms (the Pond-B group) after transfer to the RAS were evaluated in pond-nursed fry. Their survival and morphometric indices were monitored after the RAS habituation period (first 10 days), after the 18-day post-habituation period and after an additional 30 days of on-grow. Our results indicate a negative allometric growth of the pond-nursed fish during the nursing period, which was slower (p < 0.0001) in comparison to the RAS-nursed fry (16.3 ± 0.4 vs. 17.8 ± 0.7%/day). After transfer, these fish grew faster than the RAS-nursed fry (7.7 ± 0.1, 4.9 ± 0.5 and 6.1 ± 0.6 during habituation, 8.5 ± 0.6, 9.3 ± 0.5 and 6.7 ± 0.1%/day during post-habituation period, in the Pond-B, Pond-D and RAS groups, respectively). However, four weeks afterwards, the RAS-nursed fry were again superior in terms of growth (4.0 ± 0.1, 3.6 ± 0.2 and 4.6 ± 0.2%/day, for the Pond-B, Pond-D and RAS groups, respectively), and this was accompanied by a significantly lower feed conversion ratio in this group. Although the survival of the RAS-nursed fry during the nursing period was lower in comparison to the pond-reared fry (11.3 vs. 67.3%), the RAS seems to provide a long-term growth advantage.

Optimizing the gonadoliberin dosage and evaluating the egg quality in the preseason and seasonal artificial reproduction of pond-reared sterlet Acipenser ruthenus.

Sterlet Acipenser ruthenus is the smallest in size, early maturing, yet third in production scale among the sturgeon species and as such presents a good model to study reproductive biology. The present study aimed to evaluate the effects of preseason artificial reproduction and reduction of hormonal dosage on the egg quality in pond-reared sterlet. Therefore, a series of three trials were conducted in the period 2021 and 2022 (21 and 22) that evaluated three dosages of mammalian gonadotropin releasing hormone analog des-Gly10-(d-Ala6)-GnRH (40, 20, and 10 µg/kg) in both preseason (January) and seasonal (April) spawning batches (PRE and SEA). The greatest embryo survival was achieved in SEA-21-10 (84.8 ± 5.8 %) and the lowest in PRE-21-40 (31.0 ± 40.7 %). Overall results indicated that a dosage of 10 µg/kg leads to the highest embryo survival. Considering the season, latency time was significantly longer in preseason reproduction being on average about 6 h prolonged (35.1 ± 2.8 h vs. 41.4 ± 2.9 h) and it directly affected the embryo survival (linear correlation r = - 0.769, P = 0.003). Likewise, preseason reproduction yields more variable egg quality, due to impaired performance of later ovulating fish most likely due to lower oocyte maturation competence. The present study found expected latency time at 14 °C to be 37-41 h in the preseason and 31-41 h in season, while the recommended dosage is 10 µg/kg des-Gly10-(d-Ala6)-GnRH. Future studies should develop in vitro tools to evaluate the oocyte maturational competence to improve the egg quality in the preseason.

Fish with larger pre-seasonal oocytes yields lower egg quality in season - A case study of outdoor-cultured domesticated Pikeperch (Sander lucioperca).

Seasonal reproduction of domesticated pikeperch has been the most critical spawning batch in several European countries. The present study aimed to monitor oocyte growth between mid-November and seasonal spawning to evaluate if oocyte growth trends may predict egg quality. Nineteen sexually mature females were monitored for oocyte sizes every two months. In mid-March, fish were transported to the indoor facility and artificially reproduced. Sixteen females ovulated and egg quality parameters were assessed and further related to oocyte sizes measured in November, January, and March, as well as to size increments between samplings. Based on the oocyte diameters, fish were assigned to two size groups, and the egg quality was compared. Oocyte growth was greater between the first two samplings compared to the consecutive period (150.1 ± 16.5 µm vs 24.7 ± 20.4 µm). Diameters assessed in November and March positively correlated with oil globule fragmentation, while diameters assessed in November and January positively correlated with larval malformation. Although in January larger oocytes showed better embryo survival than smaller ones (60.6 ± 9.5% vs 37.8 ± 23.2%,) they were characterized with greater percent of malformed larvae (25.0 ± 22.0% vs 5.4 ± 3.9%). It appears that fish with bigger oocytes in pre-season have an affinity toward increased embryo survival, however, they seem to have an issue with oil globule fragmentation and larvae malformation in case of seasonal spawning. Therefore, the selection of breeders for either pre-seasonal or seasonal reproduction batch according to the November oocyte size is recommended.

Effects of Hydrostatic Pressure Treatment of Newly Fertilized Eggs on the Ploidy Level and Karyotype of Pikeperch Sander lucioperca (Linnaeus, 1758).

We studied the effect of different magnitudes (7000 PSI (48.26 MPa), 8000 PSI (55.16 MPa), and 9000 PSI (62.05 MPa)) of hydrostatic pressure on the ploidy of pikeperch larvae. Pressure shock was applied 5 min after the fertilization of eggs at a water temperature of 14.8 ± 1 °C. A 7000 PSI pressure shock was applied for 10 or 20 min, while 8000 and 9000 PSI treatments lasted for 10 min. Each treatment with its respective control was completed in triplicate, where different females' eggs served as a replicate. In the treatment groups exposed to 7000 PSI for 10 min, only diploid and triploid larvae were identified, while 2n/3n mosaic individuals were found after a 20-min exposure to a 7000 PSI pressure shock. The application of 8000 or 9000 PSI pressure shocks resulted in only triploid and mosaic individuals. Among larvae from eggs treated with 8000 PSI, three mosaic individuals with 2n/3n karyotype were identified (4.0 ± 6.9%), while a single (2.0 ± 3.5%) 1n/3n mosaic individual was found in the 9000 PSI-treated group. To our knowledge, this is the first report that demonstrates the induction of a haplo-triploid karyotype by hydrostatic pressure shock in teleost fish. The dominance of triploid individuals with a reasonable survival rate (36.8 ± 26.1%) after 8000 PSI shock supports the suitability of the hydrostatic pressure treatment of freshly fertilized eggs for triploid induction in pikeperch.

Effects of hormonal treatment before water warming on synchronisation of spawning time, oocyte size, and egg quality in pikeperch (Sander lucioperca).

Inducing reproduction during periods of the year when spawning typically does not occur is an important goal for the feasibility of commercial fish farming. Pre-seasonal propagation of pikeperch generally occurs about 3 months before the natural spawning season. The objective of this study was to assess effects of imposing a thermal schedule for control of water temperature and differing salmon gonadotropin releasing hormone analogue (sGnRHa) dosages on final stages of oocyte growth, and egg quality by optimizing protocol duration and synchronizing spawning time. In Experiment 1, there was analysis of thermal schedule effects for water temperature control when hormonal administrations occurred before or after water warming (WARMING and STABLE, respectively). In Experiment 2, there was assessment of the sGnRHa dosage effects during the warming schedule. In both experiments there was analysis of oocyte diameter from time of sGnRHa administration until the late stages of maturation. There was greater synchrony in time of spawning in specimens of the WARMING group with lesser variability in time from sGnRHa administration to spawning. In Experiment 2, values for reproductive variables were variable among the different groups, without any differences between treatments. Oocyte diameter at the time of sGnRHa administration was correlated with embryo survival. For effective pre-seasonal pikeperch propagation, the selection of breeders based on oocyte diameter, and administration of 5 µg/kg sGnRHa immediately upon transport to hatchery, followed by a 1 °C/d temperature increase to 10 °C, are effective methods for induction of spawning during periods when spawning does not naturally occur.

Solid state treatment with Lactobacillus paracasei subsp. paracasei BGHN14 and Lactobacillus rhamnosus BGT10 improves nutrient bioavailability in granular fish feed.

The aim of this research was to improve nutritive value of fishmeal-based feed by lactobacilli in order to achieve satisfactory nutrient availability needed to support fish development. Feed was solid-state treated at a laboratory scale with the combination of Lactobacillus paracasei subsp. paracasei BGHN14 and Lactobacillus rhamnosus BGT10 in different experimental settings, which included the variation of strain ratio, total lactobacilli concentration, percentage of moisture and duration of incubation. Short peptides, soluble proteins, phospho-, neutral and unsaturated lipids were quantified. Differences among treated and control feeds were evaluated by Student t-test, while Gaussian process regression (GPR) modeling was employed to simulate the incubation process and define the optimal treatment combination in the context of overall feed nutritional profile. Treatment duration was shown to be the critical determinant of final outcome, either as single factor or via interaction with strain ratio. Optimal nutrient balance was achieved with 12 h incubation period, 260% moisture, 75:25 and 50:50 BGHN14:BGT10 ratios and 200 mg of lactobacilli per g of dry feed. This study should serve as the basis for large-scale tests which would simulate on-farm production of both fishmeal-based and unconventional, lower cost aquafeed with added value.

Supplementation of lactobacilli improves growth, regulates microbiota composition and suppresses skeletal anomalies in juvenile pike-perch (Sander lucioperca) reared in recirculating aquaculture system (RAS): A pilot study.

This research aimed to test the effects of lactobacilli, applied to cultured pike-perch, either through hydrolyzed OTOHIME fish diet, or through Artemia nauplii, on fish growth, microbiota balance and skeletal development. On the 12th Day Post Hatching (DPH) fish were divided into following treatment groups: two groups received the combination of OTOHIME and nauplii enriched either with Lactobacillus paracasei BGHN14+Lactobacillus rhamnosus BGT10 or with Lactobacillus reuteri BGGO6-55+Lactobacillus salivarius BGHO1, and one group received OTOHIME hydrolyzed by BGHN14+BGT10 and non-enriched nauplii. Control group received non-enriched nauplii and non-hydrolyzed OTOHIME. The treatment lasted 14days and fish were sacrificed on the 26th DPH for the assessment of digestive enzyme activity and microbiota composition. Individual total lengths and individual body weights were recorded at the end of the treatments, on the 26th DPH, and also on the 45th DPH, in parallel with the evaluation of skeletal deformities and fish survival. Our results indicated positive effect of Artemia enriched with BGGO6-55+BGHO1 on fish growth, skeletal development and trypsin to chymotrypsin activity ratio (T/C), as an indicator of protein digestibility. Hydrolysis of OTOHIME was also associated with better skeletal development, higher T/C values and lower levels of Aeromonas and Mycobacterium spp., which are important fish pathogens. Though additional testing in larger cohort studies is needed, these observations are promising in terms of usage of probiotics for improved environmentally friendly production of pike-perch in Recirculating Aquaculture System (RAS).