Effect of light quality and eyestalk ablation on ovarian maturation in Penaeus monodon

Contribution No. 99, Aquaculture Department, SEAFDEC.Prawns were subjected to the following treatments: blue light, red light, natural light, and natural light plus unilateral eyestalk ablation. Unablated prawns under blue and natural light developed stage III ovaries; under red light ovarian maturation reached only stage II. Ablation resulted in full maturation of ovaries and subsequent spawning. The external changes of the ovary were generally the same for both the ablated prawns under natural light and the unablated under different light qualities. Under blue light, however the ovary at stage III had numerous atretic cells and the diameter of its ova was more uniform. The maturation stage and mean gonadosomatic indices were high for the ablated and low for the unablated prawns

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

SEAFDEC Aquaculture Department Contribution No. 233.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 wildprawns 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

Effect of substrate types on fecundity and nauplii production of ablated Penaeus monodon Fabricius.

Contribution No. 84 of the SEAFDEC Aquaculture Department.The survival, spawning, fecundity, and nauplii production of ablated Penaeus monodon females reared in flow-through broodstock tanks with white coralline and black sand substrates for 62 days, were assessed. Prawns exposed to the white coralline substrate consistently produced eggs with significantly higher (P - 0.05) average hatching rates and total nauplii production than those exposed to the black sand substrate. No differences were observed in the fecundity, spawning and survival rates in both treatments. It was observed that nightly sampling of ablated females during experiment 2 produced a higher number of spawning (48) and total number of nauplii produced (6.8 milion) compared to twice weekly sampling in experiment I (29 spawnings and 3.0 million nauplii) for the white substrate

Tissue lipid content and fatty acid composition during ovarian maturation of ablated Penaeus monodon

The total lipid content and fatty acid composition in the hepatopancreas, muscle and gonad of ablated Penaeus monodon females at ovarian maturation Stages I to V were examined. The lipid content was highest in the hepatopancreas, 22.5% to 34.9% dry wt. There was no marked variation with maturation stage in muscle lipid levels. Ovarian lipid content more than doubled the initial value of 7.5% at commencement of maturation Stage II, and progressively increased to a maximum of 21.9% at full maturity (Stage IV), corollary to a rise in hepatopancreas lipid. The findings suggest lipids are stored and utilized for gonadal development and spawning. Fatty acid profiles in the tissues showed a predominance of 20:4n-6, 20:5n-3 and 22:6n-3 polyunsaturated fatty acids (PUFA). The characteristically high levels of PUFA in mature shrimp ovaries and presence in spawned eggs are indicative of their metabolic and physiological importance in penaeid shrimp reproduction

Effects of different sex ratios on maturation, fecundity and hatching rates of ablated Penaeus monodon wild stock.

The minimum number of males per female that would still ensure high maturation, fecundity and hatching rates in Penaeus monodon broodstock, is determined. Wild stock P. monodon were stocked in 4 m diameter circular tanks at different sex ratios (0:1, 1:1, 1:2 and 1:4 male to female) for a duration of 55 days. All females were ablated on one eyestalk. Males remained unablated. The 1 male: 2 females ratio is recommended on the basis of highest percentage of first, second and third spawners, total and average fecundity. In the all-female treatment (0:1 ratio), 19.65% of the females spawned, but the 3.3 million eggs produced were not fertilized, resulting in a 0% hatching rate

The effect of diet on the reproductive performance of pond-reared Penaeus monodon Fabricius broodstock

Three practical diets were tested for their effects on the reproductive performance, survival and larval quality of pond-reared Penaeus monodon. Diets A, B and C were formulated to contain the same basal components but supplemented with different sources of lipids. Lipid sources were cod liver oil (Diet A), soybean lecithin (Diet C) or their 1:1 combination (Diet B). An all-natural diet consisting of squid and marine annelids served as control. Pond-raised P. monodon were stocked in four 12-m3 flow-through maturation tanks with 28 females and 22 males per tank. Broodstock were acclimated to the diets prior to unilateral ablation of females. Reproductive performance in terms of total number of spawnings, eggs and nauplii production, average hatch rate of eggs and larval quality was best for Diet A followed by Diet C. Diet B gave the poorest overall response but was better than the control. In the control most of the mature females resorbed their ovaries and failed to spawn; survival rates of females was also lowest. The results suggest that nutritional quality of broodstock diet affects reproduction and larval survival. Diet A (cod liver oil supplemented) was found to be a suitable diet for successful maturation and spawning of pond-reared P. monodon