Josefa D. Tan-Fermin

Ovarian maturation stages of the wild giant tiger prawn, Penaeus monodon Fabricius

Abstract A qualitative and quantitative study of the ovarian maturation stages of wild-caught Penaeus monodon was conducted to refine the existing method of staging. For industrial purpose, measuring the ovarian width at the first abdominal region can minimize arbitrariness in staging. A width of 20 mm indicates readiness for spawning while reproductive performance is improved when ovarian width is 30 mm or more. Based on histology, the usual 6 to 8 stages of development can be reduced to four stages: previtellogenic, vitellogenic, cortical rod, and spent. The previtellogenic stage (P) is characterized by the predominance of oogonia and primary oocytes in the chromatin nucleolus and/or perinucleolus stage. The vitellogenic stage (V) is marked by the presence of yolky oocytes. The cortical rod stage (C) is distinguished by the appearance of yolky oocytes with spherical or rod-like bodies at the peripheral cytoplasm. The spent stage (S) can be distinguished by the presence of few oocytes with yolky substance and/or cortical rods, thicker layers of follicle cells, and few darkly-stained, irregularly shaped primary oocytes. Individuals classified as stages II+ and III+ showed similarity in size and shape of all lobes in the posterior thoracic region, and histologically, corresponded to the revised stages V and C, respectively. Histochemical staining shows that glycoproteins and lipids are absent in the primary oocytes and present in yolky oocytes. Glycoproteins but not lipids occur in the cortical rods. Analysis of variance showed significant differences in mean gonad weight and gonadosomatic index values but not in the mean body length and body weight values in stages P to C. Uniformity in the number, stage and composition of oocytes in the four regions of the ovary at each stage showed that stage of ovarian maturity in wild prawns can be represented by any region of the ovary. Differences in the oocyte size frequency and mean values of average and maximum oocyte diameter in the four stages showed that these are good indicators of stage of maturation in wild P. monodon .

Seminal plasma composition, sperm motility, and milt dilution in the Asian catfish Clarias macrocephalus (Gunther)

Abstract Ionic composition of the seminal plasma and factors that initiate sperm motility in the freshwater Asian catfish Clarias macrocephalus , were examined to develop an artificial seminal plasma (ASP) that can be used to dilute milt. The optimum ratio of milt:ASP that can reversibly activate the sperm and milt–ASP:ovulated eggs that will result in high fertilization rates were further determined to minimize the number of males to be sacrificed during artificial insemination. Seminal plasma of C. macrocephalus contained 17.8±0.1 mM/l potassium, 164.4±0.6 mM/l sodium, 8.4±0.0 mM/l calcium and 1.6±0.0 mM/l magnesium, and had an osmolality of 269.0±6.4 mOsm/kg, and pH of 7.8±0.2. Sperm motility was highest and longest in all electrolyte (NaCl, CaCl 2 , KCl) and non-electrolyte (mannitol) solutions of 200 mOsm/kg. Catfish sperm were motile in all isotonic NaCl–KCl solutions, and were reversibly activated in the ASP (143 mM NaCl, 30 mM KCl, 8 mM CaCl 2 , 2 mM MgCl 2 , 10 mM HEPES) solutions of pH 6.4–9.4. Altogether, these results suggest that sperm motility in C. macrocephalus was mainly initiated by a decrease in osmotic pressure, rather than ions and pH. High fertilization rates (89–94%) were observed when 10 μl milt, diluted with 1000 μl ASP, was activated with 5 ml of 0.6% NaCl (198.24 mOsm/kg) to fertilize 5 or 10 g of ovulated eggs. Results obtained from the present study provide information on sperm physiology that will lead to more efficient gamete management, and hopefully, an increase in the yield of catfish fry in the hatchery.

Effects of unilateral eyestalk ablation on ovarian histology and oocyte size frequency of wild and pond-reared Penaeus monodon (Fabricius) broodstock

Abstract Effects of eyestalk ablation on ovarian maturation of wild and pond-reared Penaeus monodon were determined to compare their reproductive potential. This was done by counting the oocyte size frequency in four regions of the ovary and comparing the percentage of each cell type present at each stage of maturation per group. Sampling of ablated prawns was done during three maturation or spawning periods within the first molt cycle after ablation. It took 5 and 14 days for wild and pondreared prawns, respectively, to show signs of ovarian maturation after ablation. Percentage of proliferating cells, the smallest germinal cells in the prawn ovary, was higher in wild unablated (8.3%) than ablated (2.5–5.0%) groups. Significant differences were observed in all cell types at different stages of maturation. In both unablated and ablated prawns, there was a uniform development of the whole ovary and similar occurrence of atresia at all stages. The presence of bigger oocytes in the ovaries of ablated prawns sampled after spawning provided histological evidence for lower number of eggs per spawn and faster rematuration.

Marine leech (Zeylanicobdella arugamensis) infestation in cultured orange-spotted grouper, Epinephelus coioides

Heavy infestation of a marine leech occurred among tank-reared juvenile and adult orange-spotted grouper, Epinephelus coioides Hamilton, at SEAFDEC AQD, Philippines with a prevalence of 83% and 17%, respectively. The leeches were attached in large numbers on the fins, lower jaw, under the operculum, eyes, and inside the mouth of the fish. The attachment and feeding sites exhibited frayed fins, hemorrhages and swelling of the hosts skin. External and internal features indicate that the leech is Zeylanicobdella arugamensis De Silva (Hirudinea, Piscicolidae). The parasite can be effectively controlled using 50 ppm formalin bath treatment for 1 h.

LHRHa and pimozide-induced spawning of Asian catfish Clarias macrocephalus (Gunther) at different times during an annual reproductive cycle.

Abstract Captive Clorias macrocephalus were induced to spawn during the off-season (February), before (May), during (August) and end (November) of the natural breeding period to test their seasonal responsiveness to hormone treatment, and assess the resulting egg and larval quality. Intramuscular injections were given to five fish in each treatment consisting of 0.05 μg LHRHa + 1 μg PIM g −1 body weight (BW), 0.05 μg LHRHa, 1 μg PIM, or LHRHa vehicle (0.9% NaCl) and PIM vehicle (1 dimethylsulfoxide: 9 propylene glycol, v/v). At any phase of the annual cycle, only fish injected with a combination of LHRHa and PIM spawned, although initial egg size was similar among fish within a season. However, initial egg size was largest in fish induced to spawn in May (1.59 mm), followed by fish induced in August and November (1.54 mm), and smallest in fish induced in February (1.49 mm). All fish ovulated when induced to spawn in May and August, but ovulation rates decreased to 80% and 60% when fish were injected in November and February, respectively. Catfish induced to spawn in May, August and November had higher egg production, fertilization and larval survival rates than the fish induced in February. Hatching rates were higher in fish induced in May and August than in February, while hatching rate of fish induced in November was similar to those spawned at other times of the year. These results provide useful information regarding the broodstock management and hatchery production of C. macrocephalus .