Lisa Ann Sorbera

Effects of Polyunsaturated Fatty Acids and Prostaglandins on Oocyte Maturation in a Marine Teleost, the European Sea Bass (Dicentrarchus labrax)

Abstract The effects of the polyunsaturated fatty acids (PUFAs), arachidonic acid (AA), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and prostaglandins (PGs) on oocyte maturation were investigated in a marine teleost, the sea bass (Dicentrarchus labrax). Follicle-enclosed postvitellogenic, preovulatory oocytes were cultured in vitro and maturation was verified by assessing volume increase, lipid droplet coalescence, yolk clarification, and germinal vesicle migration and breakdown. Human chorionic gonadotropin was administered as the maturation-inducing gonadotropin (GTH) and was capable of inducing maturation in a time- and dose-dependent manner. Free AA induced maturation in a dose- and time-dependent manner and enhanced GTH-induced maturation, while EPA, DHA, and oleic acid were ineffective. Maturation induced by GTH was significantly suppressed by a phospholipase A2 blocker, suggesting that mobilization of AA was involved in GTH-induced maturation. Moreover, EPA and DHA exhibited a significant, dose-dependent attenuation of GTH-induced maturation. Maturation induced by GTH was inhibited in the presence of a cyclooxygenase inhibitor, indomethacin, and this inhibition was reversed by addition of AA, PGE2, or PGF2α. PGE2 and PGF2α alone were both effective stimulators of maturation, while PGE1 and PGE3 were ineffective. The effect of PUFAs on oocyte maturation in vitro were corroborated with studies in vivo. Oocytes were obtained from females fed a commercial, PUFA-enriched diet (RD) and maturational behavior was compared with oocytes from females fed a natural diet (ND) with a higher EPA content and n-3:n-6 ratio. Although no significant difference was observed in the rate of spontaneous oocyte maturation, a higher percentage of GTH-induced maturation and lower percentage of atresia were observed in RD oocytes. Moreover, while basal PGE production from oocytes from both groups was the same, RD oocytes produced significantly higher levels of PGE in the presence of hCG. The results from this study provide evidence for the participation of AA metabolism in GTH-induced oocyte maturation, and suggest that other PUFAs and PGs may play important roles in the induction of maturation in a marine teleost.

Reproductive performance in male European sea bass (Dicentrarchus labrax, L.) fed two PUFA-enriched experimental diets: a comparison with males fed a wet diet

Abstract Reproductive performance of male European sea bass ( Dicentrarchus labrax ) fed a wet diet (WD) was compared to that of fish fed two commercial pelleted diet enriched with polyunsaturated fatty acids (PUFAs) by the use of Northern hemisphere fish oil (ST) or tuna orbital oil (RO). Broodstock growth, spermiation duration, milt production, milt spermatozoa density, sperm motility, milt lipid composition, and fertilization rates were compared during the reproductive season. RO and ST males exhibited longer spermiation periods producing statistically higher milt volumes and milt spermatozoa densities as compared to WD; no differences in quality or motility of sperm were observed between groups. Although the fertilization rates of RO, ST and WD milt at 3 and 24 h after fertilization were similar (88–90%), significantly higher rates of embryonic and larval survival were observed at 48 and 72 h after fertilization from eggs fertilized with ST (13.9% and 15.5%) and RO milt (20.9% and 20.6%) as compared to WD (1.0% and 1.2%). Analysis of milt PUFA profiles revealed several differences between groups. Although total PUFAs were increased in all groups as compared to diet PUFA composition, a greater increase was noted for ST and RO. In January and March, fish fed the WD exhibited more weight gain and attained significantly higher weights, respectively, than RO fish. Results showed that although fish fed the WD displayed increased weight gain, reproductive performance was enhanced in males fed the commercially fabricated diets possibly reflecting benefits of PUFA-enrichment.

Sustained administration of GnRHa increases milt volume without altering sperm counts in the sea bass

The role of gonadotropin-releasing hormone (GnRH) in spermiogenesis and spermiation is not well understood. This study examined the effects of different modes of administration of a GnRH analog (GnRHa; [D-Ala6,Pro9NEt]-mGnRH) on spermiation in the sea bass, Dicentrarchus labrax. Groups of sea bass received either GnRHa injection in saline (I; 25 μg/kg body weight [BW] or one of three types of GnRHa sustained release polymeric device: a fast-releasing implant (ethylene-vinyl acetate copolymer [EVAc]; 100 μg/kg BW), a slower-releasing implant (ethylene-vinyl acetate copolymer [EVSL]; 100 μg/kg BW), or biodegradable microspheres (M; 50 μg/kg BW). Total expressible milt was collected and assessed for volume, motility, and counts at various intervals for 44 days. Untreated males produced a total of 9.4 ± 3.4 ml/kg BW (mean ± SEM) of milt over the 44-day experimental period, with milt production ending by day 28. All GnRHa treatments stimulated a significant increase in total milt volume (ml/kg BW) peaking by day 2 (I: 11.8 ± 1.8) or day 7 (EVAc: 20.0 ± 1.5; M: 26.8 ± 2.7; EVSL: 27.9 ± 4.3) posttreatment. While milt volumes in injected males returned to control values by day 14, all groups treated with sustained GnRHa delivery systems maintained significantly elevated milt volumes for 21 days (EVAc group) or 35 days (EVSL and M groups). Sperm motility was consistently good to excellent (70–100% vigorously active) in all groups when expressible milt volume was above 1.0 ml, and there were no significant differences in sperm counts (averaging 5.5 ± 0.1 × 109 spermatozoa/ml). These data show that sustained administration of GnRHa significantly increases and prolongs spermiation in the sea bass without altering sperm concentration or quality.

Energetic dependence of NPY-induced LH secretion in a teleost fish (Dicentrarchus labrax).

The purpose of this work was to examine the role of energetic status in neuropeptide Y (NPY)-induced luteinizing hormone (LH) secretion and glucose metabolism in fish. Fasted juvenile sea bass ( Dicentrarchus labrax) were injected intraperitoneally with pig (p) NPY or pNPY + glucose, whereas fed animals were injected with pNPY alone and plasma glucose, insulin, and LH levels were examined. pNPY alone or in combination with glucose was found to induce a dose-dependent increase in LH secretion in fasted animals. Similar LH responses to pNPY were observed in vitro in dispersed pituitary cells isolated from fed and fasted animals incubated in L-15 and restricted media. Injection of pNPY + glucose in fasted animals resulted in depletion of glucose. Insulin plasma levels decreased in fasted animals coinjected with pNPY + glucose but remained stable when NPY was administrated alone to fed and fasted animals. Results suggest that 1) NPY-induced LH secretion in fish is dependent on energetic status and 2) NPY is capable of modifying glucose metabolism.The purpose of this work was to examine the role of energetic status in neuropeptide Y (NPY)-induced luteinizing hormone (LH) secretion and glucose metabolism in fish. Fasted juvenile sea bass (Dicentrarchus labrax) were injected intraperitoneally with pig (p) NPY or pNPY + glucose, whereas fed animals were injected with pNPY alone and plasma glucose, insulin, and LH levels were examined. pNPY alone or in combination with glucose was found to induce a dose-dependent increase in LH secretion in fasted animals. Similar LH responses to pNPY were observed in vitro in dispersed pituitary cells isolated from fed and fasted animals incubated in L-15 and restricted media. Injection of pNPY + glucose in fasted animals resulted in depletion of glucose. Insulin plasma levels decreased in fasted animals coinjected with pNPY + glucose but remained stable when NPY was administrated alone to fed and fasted animals. Results suggest that 1) NPY-induced LH secretion in fish is dependent on energetic status and 2) NPY is capable of modifying glucose metabolism.