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Changes in external osmolality and ionic composition affect Megaleporinus obtusidens sperm motility
Jurandir Joaquim Bernardes Júnior1, Jhon Edison Jimenez1, Robie Allan Bombardelli2
1Laboratório de Biologia e Cultivo de Peixes de Água Doce (LAPAD), Departamento de Aquicultura, Centro de Ciências Agrárias, Universidade Federal de Santa Catarina, Rodovia SC 406, 3532, Florianópolis, Santa Catarina CEP 88066-000, Brasil.
Abstract:
Understanding the effects of environmental factors on sperm motility characteristics can increase artificial reproduction efficiency in species that do not spawn naturally in captivity, such as Megaleporinus obtusidens. This study evaluated the effects of the osmolality (25, 85, 145, 205, 265, and 325 mOsm kg-1) and composition of activating solutions (NaCl, KCl, or fructose) on the percentage of motile sperm, and the swimming velocity and path straightness of M. obtusidens spermatozoa. The concentrations of major ions in the seminal fluid were also assessed and Na+ (74.46 mmol L-1), K+ (37.24 mmol L-1), and Cl- (114.29 mmol L-1) were the most abundant. When the activating solution was hypertonic (325 mOsm kg-1) compared to the seminal fluid (293 mOsm kg-1), sperm motility was completely inhibited. A wide range of osmolalities that initiated sperm motility were identified for all three solutions. Both, the percentage of motile sperm and the motility duration were reduced (P < .05) at extreme osmolalities. At 145 mOsm kg-1, the percentage of motile sperm remained high (>50%) up to 40 s after activation and the motile phase lasted for >50 s, regardless of the activating solution composition. Over the postactivation time, the curvilinear velocity and straightness were similar (P > .05) for fructose and NaCl solutions, whereas KCl solutions induced a higher (P < .05) curvilinear velocity, lower (P < .05) straight-line velocity, and a circular swimming motion in spermatozoa. Our results suggest that a reduction in osmolality, using both non-electrolyte and electrolyte solutions, is the main trigger for the onset of spermatic movement in M. obtusidens sperm.
Insights
Reducing osmolality of activating solutions triggers sperm movement in Megaleporinus obtusidens. Optimal osmolality enhances sperm motility percentage and duration, crucial for artificial reproduction.
Area of Science:
- Reproductive Biology
- Ichthyology
- Environmental Physiology
Background:
- Artificial reproduction efficiency in captive-bred species like Megaleporinus obtusidens is limited by a lack of understanding of environmental factors affecting sperm.
- Sperm motility is a critical factor in successful fertilization and artificial reproduction, influenced by external conditions.
- Megaleporinus obtusidens does not spawn naturally in captivity, necessitating research into optimizing its artificial reproduction.
Purpose of the Study:
- To evaluate the impact of osmolality and activating solution composition on Megaleporinus obtusidens sperm motility.
- To determine the optimal osmolality and solution type for maximizing sperm motility percentage, velocity, and duration.
- To identify the key environmental trigger for initiating spermatic movement in this species.
Main Methods:
- Spermatozoa from Megaleporinus obtusidens were activated using solutions with varying osmolalities (25-325 mOsm kg⁻¹) and compositions (NaCl, KCl, fructose).
- Sperm motility parameters, including percentage of motile sperm, swimming velocity, and path straightness, were assessed.
- Major ion concentrations (Na⁺, K⁺, Cl⁻) in seminal fluid were analyzed.
Main Results:
- Sperm motility was completely inhibited in hypertonic solutions (325 mOsm kg⁻¹).
- Optimal motility (high percentage and duration) was observed at 145 mOsm kg⁻¹ across all tested solution types.
- KCl solutions increased curvilinear velocity but decreased straight-line velocity, inducing a circular swimming pattern, while NaCl and fructose showed similar effects on velocity and straightness.
Conclusions:
- A reduction in osmolality is the primary trigger for initiating sperm movement in Megaleporinus obtusidens.
- Osmolality levels between 25 and 145 mOsm kg⁻¹ effectively activate sperm motility.
- Findings provide crucial data for optimizing artificial reproduction protocols for Megaleporinus obtusidens.
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