Delay of the egg activation process in the Black Tiger Shrimp Penaeus monodon by manipulation of magnesium levels in spawning water

The aim of this study was to determine whether magnesium (Mg²⁺) in seawater is required for egg activation of the black tiger shrimp Penaeus monodon and whether manipulation of Mg²⁺ levels can be used to delay the process and thereby synchronize egg activation. Female P. monodon broodstock were allowed to spawn in artificial seawater containing Mg²⁺ at varying levels with respect to the normal (100%) level: 100%, 50%, 20% and 0%. Egg activation occurred normally at 100% Mg²⁺, incompletely at 50% and 20% Mg²⁺ levels and did not occur at all with 0% Mg²⁺. The fertilization rate with 100% Mg²⁺ was observed to be 83%, but fertilization failed to take place in all the other groups. The fertilization rate was restored from 0% to 76% following the 20% Mg²⁺ level treatment when Mg²⁺ levels returned to normal (100%) as soon as spawning was completed. This study suggests that the level of Mg²⁺ in seawater plays a vital role in P. monodon egg activation, and that commencement of this process could be delayed by manipulation of the Mg²⁺ level during and immediately after spawning.     

Biochemical characterization and physiological role of cortical rods in black tiger shrimp, Penaeus monodon

Cortical rods (CRs), precursors of egg jelly investment in many penaeoid shrimp, are composed of different proportions of proteins and carbohydrates, the physiological role of which still requires extensive investigation. In this study, we demonstrated the biochemical properties of the CRs and their role in the induction of the acrosome reaction (AR). Profiles of the isolated CRs revealed a number of major protein bands ranging from 35 to 230 kDa. These CR proteins were extensively glycosylated and sulfated. Lectin-based carbohydrate analysis further revealed the highest reactivity of concanavalin A (Con A) among other lectins used. In addition, the selective interference of Con A binding with mannose but not glucose indicated that CR glycoproteins were of high-mannose type. Using immunoblotting with anti-CR antibody, we further demonstrated that part of egg water (EW, a natural AR inducer) was derived from miscible components of the CRs. Physiological tests of water-soluble CR (wsCR) revealed its high AR inducing competency comparable to that of EW, which was far superior to that of acid-urea treated CR (auCR). Furthermore, the wsCR-induced AR was selectively inhibited by Con A, suggesting the significance of the exposing mannose residues in regulating P. monodon sperm AR response.     

Hatching envelope formation in the egg of the black tiger shrimp,Penaeus monodon (Decapoda,Penaeidae)

The aim of this study was to reveal the process of hatching envelope (HE) formation in eggs of the black tiger shrimp Penaeus monodon, using fluorocytochemistry with fluorescein isothiocyanate (FITC)‐labelled lectins and transmission electron microscopy (TEM) with mouse monoclonal anti‐FITC‐conjugated gold‐lectin labelling. Following lectin binding screening tests, Concanavalin A (Con A) and wheat germ agglutinin (WGA) were chosen to trace movements of specific sugar‐associated components of the HE. This revealed that both Con A and WGA‐binding components migrated from the ooplasm to the HE. Using TEM, it was revealed that membranous materials in the ooplasm were released at the time of spawning, that these became associated with granular structures outside the oocyte and that they together developed into an outer layer of the HE. Contents of flocculent vesicles and dense vesicles in the ooplasm were exocytosed and formed the inner layer of the HE. The TEM with gold‐labelled Con A and WGA revealed that the dense and flocculent vesicles and the inner layer of the HE contained components associated with mannose (sugar affinity to Con A) and N‐acetyl‐β‐d ‐glucosamine (sugar affinity to WGA).     

Fish condensate as effective replacer of fish meal protein in diet for striped snakehead, <Emphasis Type="Italic">Channa striata</Emphasis> (Bloch)

The optimal protein replacement of fish meal (FM) by fish condensate (FC) was investigated in striped snakehead, Channa striata (Bloch) (1.78 ± 0.02 g initial weight). The FM-based diet (0FC) was replaced by substituting protein from FC for 100 (100FC), 200 (200FC), 300 (300FC), 400 (400FC), 500 (500FC) or 600 (600FC) g kg^?1 of the FM, and a commercial diet (CD) for carnivorous fish was included for comparison. The experiment was conducted indoors under completely randomized design (8 treatments × 3 replications × 60 fish per pond) over a 6-month trial. There were no significant differences in water quality during the experiment. The fish fed with 500FC had superior growth performance and feed utilization. This dietary treatment gave similar levels to all observed specific activities of digestive enzymes as did baseline 0FC. Survival, carcass composition, hematological parameters and liver histopathology were not negatively impacted by this protein replacement level. Economic analysis also supports the use of this by-product as a potent protein replacer in striped snakehead diet. Findings from the current study indicate that a 500 g kg^?1 protein replacement of FM by FC is near optimal for striped snakehead, and similar use of it in the aquafeed of other species appears worth further studies.     

The existence of gonadotropin-releasing hormone (GnRH) immunoreactivity in the ovary and the effects of GnRHs on the ovarian maturation in the black tiger shrimp Penaeus monodon

Immunocytochemical localization using antibodies against five isoforms of gonadotropin-releasing hormone (GnRH), namely, luteinizing hormone-releasing hormone (LHRH), salmon (s)GnRH, octopus (oct)GnRH, lamprey (l)GnRH-I, and lGnRH-III, showed that only lGnRH-I immunoreactivity (ir-lGnRH-I) was localized in follicular cells of proliferative, vitellogenic, and mature ovaries. The effects of exogenous GnRHs on the ovarian maturation cycle of Penaeus monodon were compared by treating female broodstocks with LHRH, sGnRH, and lGnRH-I. The cycle of ovarian maturation in both eyestalk-ablated and eyestalk-intact shrimp administered with the three isoforms of GnRH was significantly shorter than that of the control animals. Moreover, administrations of all GnRH isoforms showed similar numbers of spawned eggs and the percentage of successful fertilization as in the control animals. These findings suggest that GnRHs may be highly conserved peptides that play an important role in inducing the ovarian maturation in the shrimp.     

Salinity tolerance of cross‐breed shrimp families: morphological and biochemical approaches

Marine invertebrates respond to fluctuations in their environment throughout development and growth. Homeostatic adaptation is mediated in part through the regulation of Na⁺‐K⁺ ATPase enzymes and members of this class of enzymes are localized to the antennal gland of many crustaceans. In this study, we investigated the morphological and biochemical changes of the antennal glands in eight families of cross‐breed post‐larval shrimp subjected to hypotonic (10 ppt) and isotonic (20 ppt) conditions. The greatest changes in the antennal glands were detected in the hypotonic condition with families two and five cross‐breed shrimp exhibiting the highest tolerance to this diluted salinity. The changes detected in hypotonic tolerant shrimp included enlargement of coelomosac and labyrinth spaces, the presence of many dense cytoplasmic globules in podocytes as well as highly wavy apical architecture of labyrinth cells. Several alterations were also observed at the subcellular level such as widening of the intercellular spaces between podocytes, organelle destruction, and decreased basal membrane in‐folding in labyrinth cells. In addition, shrimp exposed to hypotonic conditions displayed decreased expression of both α and β subunits of Na⁺‐K⁺ ATPase and decreased enzymatic activity. The changes observed in animals upon exposure to hypotonic stress are discussed.     

Optimal protein replacement of fish meal by mackerel condensate in diet for giant freshwater prawn (Macrobrachium rosenbergii)

The optimal protein replacement of fish meal (FM) by mackerel condensate (MC) was investigated in giant freshwater prawn, Macrobrachium rosenbergii (0.90 ± 0.01 g initial weight) over a 12‐week trial. The experimental diets replaced the FM partially in a baseline FM‐based diet (0MC), by substituting MC for 10% (10MC), 20% (20MC), 30% (30MC), 40% (40MC), 50% (50MC) and 60% (60MC) of the FM, and a commercial diet (CD) was included for comparison. The prawn fed with 40MC had superior growth performance and feed utilization. Significant increases in amylase and cellulase‐specific activities indicated improved carbohydrate utilization in this dietary group (P < 0.05). The proteolytic activity was maintained through the key gastrointestinal enzymes (pepsin, trypsin and chymotrypsin). A slight improvement in carcass compositions was also observed in the prawns fed 40MC, and the total haemocyte count was significantly increased by this diet, without negative effects on the hepatopancreatic histology. These findings indicate that a 40% protein replacement of FM by MC is optimal for giant freshwater prawn, and similar use of it in the aquafeed of other species appears worth further studies.