Effects of body mass and water temperature on routine metabolism of American paddlefish Polyodon spathula.

This study quantified the effects of temperature and fish mass on routine metabolism of the American paddlefish Polyodon spathula. Thermal sensitivity, as measured by Q(10) value, was low in P. spathula. Mean Q(10) was 1·78 while poikilotherms are generally expected to have Q(10) values in the 2·00-2·50 range. Mass-specific metabolism did not decrease with increased fish size to the extent that this phenomenon is observed in teleosts, as evidenced by a mass exponent (ß) value of 0·92 for P. spathula compared with 0·79 in a review of teleost species. Other Acipenseriformes have exhibited relatively high ß values for mass-specific respiration. Overall P. spathula metabolism appears to be more dependent on body mass and less dependent on temperature than for many other fishes. An equation utilizing temperature and fish mass to estimate gross respiration for P. spathula was derived and this equation was applied to respiratory data from other Acipenseriformes to assess inter-species variation. Polyodon spathula respiration rates across water temperature and fish mass appear most similar to those of Atlantic sturgeon Acipenser naccarii and white sturgeon Acipenser transmontanus.

Effects of ions on the motility of fresh and demembranated paddlefish (Polyodon spathula) spermatozoa.

This study investigated the effects of different environmental conditions on the motility parameters of paddlefish (Polyodon spathula) spermatozoa. Paddlefish spermatozoa demonstrated the following characteristics: (i) all spermatozoa were motile 10 s after activation with a velocity of 130-160 microm s(-1); (ii) after 2 min, velocity decreased to 80-130 microm s(-1); and (iii) motility was maintained for up to 9 min. Concentrations of 0.5-5.0 mmol KCl l(-1) prevented activation of spermatozoa. After transfer into a swimming medium (20 mmol Tris l(-1), pH 8.2 and 1 mg BSA ml(-1)) containing 0.5 mmol KCl l(-1) (combined with 5 mmol NaCl or MgCl(2) l(-1)), 80-100% of cells were motile with a velocity of about 120-150 microm s(-1). MgCl(2) significantly improved the velocity of spermatozoa at 10, 40, 50 and 60 s after activation and the stable velocity of spermatozoa was about 140 microm s(-1). Very low concentrations of CaCl(2) (0.125 mmol l(-1)) combined with 0.5 mmol KCl l(-1) initiated motility in 20% of spermatozoa, whereas all spermatozoa were activated after 2 min with 0.25 mmol CaCl(2) l(-1) in similar medium for the full period of swimming with velocity of about 120 microm s(-1). This study demonstrated that potassium (5-15 mmol l(-1)) inhibits demembranated spermatozoa. Thus, initiation of movement in paddlefish spermatozoa is under the reciprocal control of potassium and calcium ion concentrations.

Characteristics of sperm acrosin-like activity of paddlefish (Polyodon spathula Walbaum).

Spermatozoa of paddlefish and sturgeon fishes (Acipenseriformes), unlike teleost fish, have an acrosome. The objectives of this study were to characterize acrosin-like activity of cryopreserved sperm of paddlefish (Polyodon spathula) and to test and compare stability of paddlefish acrosin-like activity with that of lake sturgeon and bull spermatozoa. Mean acrosin-like activity of cryopreserved paddlefish sperm was 0.372 +/- 0.067 microU/10(6) spermatozoa. This activity was 79% higher in the whole semen than in spermatozoa. Highest activity was recorded at pH 8.0 and 8.5. Triton X-100, zinc ions and 4'-acetamidophenyl 4-guanidinobenzoate (AGB) inhibited the activity. Amidase activity was also inhibited by N-alpha-p-tosyl-L-lysine chloromethyl ketone (TLCK) and N-tosyl-L-phenylalanine chloromethyl ketone (TPCK). TLCK at concentrations of 0.1 and 1.0 mM gave a significant decrease in activity of 19 and 61%, respectively. However, TPCK significantly inhibited amidase activity (by 19%) only at concentration 1.0 mM. After acidification and 60 min incubation at 4 degrees C of sperm suspensions only 4% of the activity was retained. A similar phenomenon was observed in the case of lake sturgeon but not bull sperm. These results suggest that trypsin-like activity of Acipenserid fish resembles rather fish trypsin that mammalian one. In frozen-thawed paddlefish sperm a minute chymotrypsin-like activity was also indicated, when GPNA was used as substrate. This activity amounted to 0.0415 +/- 0.0138 microU/10(6) spermatozoa and was 18% of total amidase activity. This suggests that chymotrypsin-like activity may also be present in paddlefish spermatozoa.

Urotensin II from the river lamprey (Lampetra fluviatilis), the sea lamprey (Petromyzon marinus), and the paddlefish (Polyodon spathula).

Urotensin II was isolated from extracts of the whole brain of the river lamprey (Lampetra fluviatilis) and the sea lamprey (Petromyzon marinus). The primary structure of the peptide from both species is the same (Asn-Asn-Phe-Ser-Asp-Cys-Phe-Trp-Lys-Tyr-Cys-Val) and this amino acid sequence is identical to that of urotensin II from the dogfish and skate. Consistent with previous morphological studies indicating that the Agnatha lack a caudal neurosecretory system, urotensin II was not detected in an extract of P. marinus spinal cord. The data suggest that the urotensin II may have functioned in the earliest vertebrates as a neurotransmitter/neuromodulator in the central nervous system rather than as a neurohormone of the caudal neurosecretory system. Urotensin II was also isolated from an extract of the spinal cord of a chondrostean fish, the paddlefish (Polyodon spathula). The primary structure of the paddlefish urotensin II (Gly-Ser-Thr-Ser-Glu-Cys-Phe-Trp-Lys-Tyr-Cys-Val) is the same as that of another chondrostean, the sturgeon (Acipenser ruthenus). The study provides further evidence for a widespread distribution of urotensin II in vertebrate species and suggests that the primary structure of the peptide is better conserved in these phylogenetically ancient fish than in teleosts.