Regarding the sperm of cold-water fish, the contributions of different bioenergetic pathways, including mitochondrial respiration, to energy production at the spawning temperature and its adaptation at the maximum critical temperature (CTmax) are unclear. The roles of glycolysis, fatty acid oxidation, oxidative phosphorylation (OXPHOS) at 4 °C, and OXPHOS at 15 °C for energy production in burbot (Lota lota) spermatozoa were studied by motility and the oxygen consumption rate (OCR) (with and without pathway inhibitors and the OXPHOS uncoupler). At both temperatures, the effects of the inhibitors and the uncoupler on the motility duration, curvilinear velocity, and track linearity were insignificant; in addition, the OCRs in activation and non-activation media differed insignificantly and were not enhanced after uncoupler treatment. After inhibitor treatment in both media, OXPHOS was insignificantly different at the 2, 30, and 60 s time points at 4 °C but was reduced significantly at the 30 and 60 s time points after treatment with sodium azide at 15 °C. In conclusion, for burbot sperm at both the spawning temperature and the CTmax, the energy synthesized via OXPHOS during motility was insufficient. Therefore, the majority of the energy required to sustain motility was derived from pre-accumulated energy produced and stored during the quiescent state of the spermatozoa.

• Keywords
• cold-water fish, fatty acid oxidation, glycolysis, maximum critical temperature, oxidative phosphorylation, spawning temperature, sperm motility,
• Publication type
• Journal Article MeSH

Studying biology of sperm provides valuable information to optimize artificial reproduction and is crucial for sustainable aquaculture. Here, we investigated morphology of spermatozoon in Atlantic cod (Gadus morhua) using transmission and scanning electron microscopy. Furthermore, spermatozoa motility kinetics at different osmolalities were studied using computer-assisted sperm analysis software. The spermatozoon lacked an acrosome and consisted of a head, midpiece, and flagellum. The head of spermatozoa was round, oval, and rather elongated in shape, showing high variations in dimensions. There were up to 6 mitochondria that encircled the proximal part of the flagellum. The proximal and distal centrioles were located within the nuclear notch and arranged orthogonal to each other. The axoneme had a typical 9 + 2 microtubule structure. The flagellar length of spermatozoon was 66.94 ± 0.46 μm. Spermatozoa were immotile in the seminal plasma. Dilution of sperm with natural seawater (1100 mOsmol/kg) resulted in initiation of motility for 91.0 ± 3.4% of spermatozoa with average velocity of 86.2 ± 2.3 μm/s and beating frequency of 52 Hz. The duration of spermatozoa motility was > 6 min; however, the percentage of motile spermatozoa decreased at 60 s post-activation. When osmolality of natural seawater was modified using distilled water or NaCl, spermatozoa motility was not initiated at ≤ 400 and ≥ 2500 mOsmol/kg, and the highest percentage of motility was observed at 730-1580 mOsmol/kg. In a sucrose solution, spermatozoa motility was initiated and suppressed at 600 and 1500 mOsmol/kg, respectively, and highest percentage of motility was observed at 800-1100 mOsmol/kg. Spermatozoon morphology comparisons within Gadiformes showed differences in dimensions of head and mitochondria, flagellar length, and number of mitochondria. The present study provides valuable data that can be used for phylogenetic implications based on spermatozoon morphology and for development of artificial fertilization and sperm cryopreservation protocols based on sperm motility.

• Keywords
• Beat frequency, Electron microscopy, Ions, Osmolality, Sperm ultrastructure, Sperm velocity,
• MeSH
• Gadus morhua physiology   MeSH
• Sperm Motility physiology   MeSH
• Osmolar Concentration MeSH
• Spermatozoa physiology   ultrastructure   MeSH
• Animals MeSH
• Check Tag
• Male MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH

The lipid composition of sperm membranes is crucial for fertilization and differs among species. As the evolution of internal fertilization modes in fishes is not understood, a comparative study of the sperm lipid composition in freshwater representatives of externally and internally fertilizing fishes is needed for a better understanding of taxa-specific relationships between the lipid composition of the sperm membrane and the sperm physiology. The lipidomes of spermatozoa from stingray, a representative of cartilaginous fishes possessing internal fertilization, and sterlet, a representative of chondrostean fishes with external fertilization, have been studied by means of nuclear magnetic resonance (NMR), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), electrospray MS, gas chromatography-(GC) MS, and thin-layer chromatography (TLC). NMR experiments revealed higher cholesterol content and the presence of phosphatidylserine in stingray compared to sterlet sperm. Unknown MS signals could be assigned to different glycosphingolipids in sterlet (neutral glycosphingolipid Gal-Cer(d18:1/16:0)) and stingray (acidic glycosphingolipid sulpho-Gal-Cer(d18:1/16:0)). Free fatty acids in sterlet sperm indicate internal energy storage. GC-MS experiments indicated a significant amount of adrenic acid, but only a low amount of docosahexaenoic acid in stingray sperm. In a nutshell, this study provides novel data on sperm lipid composition for freshwater stingray and sterlet possessing different modes of fertilization.

• Keywords
• fertilization mode, freshwater fish, lipidomics, mass spectrometry, sperm, thin-layer chromatography,
• MeSH
• Chromatography, Thin Layer MeSH
• Species Specificity MeSH
• Fertilization physiology   MeSH
• Glycosphingolipids chemistry   MeSH
• Spectrometry, Mass, Electrospray Ionization MeSH
• Docosahexaenoic Acids chemistry   MeSH
• Lipidomics MeSH
• Lipids chemistry   MeSH
• Magnetic Resonance Spectroscopy MeSH
• Gas Chromatography-Mass Spectrometry MeSH
• Fishes physiology   MeSH
• Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization MeSH
• Spermatozoa chemistry   MeSH
• Animals MeSH
• Check Tag
• Male MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Glycosphingolipids MeSH
• Docosahexaenoic Acids MeSH
• Lipids MeSH