Luis Maria B. Garcia

Dose-dependent spawning response of mature female sea bass, Lates calcarifer (Bloch), to pelleted luteinizing hormone-releasing hormone analogue (LHRHa)

Abstract The induction of sequential spawnings of mature female sea bass following intraperitoneal implantation of various doses of luteinizing hormone-releasing hormone analogue (LHRHa) in a 95% cholesterol pellet was investigated. LHRHa stimulated a dose-dependent increase in spawning rate (number of spawnings per fish over a 4-day period) at doses ranging from 4.75 to 75 μg/kg body weight. Higher doses ranging from 150 to 300 μg/kg resulted in significantly fewer spawnings (62.5%–75%). Untreated control sea bass did not spawn. Sham-implanted fish failed to spawn or did so at significantly lower rates (0%–6.3%) compared to hormone-treated fish. Spawning induction at the highest hormone dose tested (300 μg/kg) resulted in the lowest mean egg fertilization rate of 30.1%. Mean fertilization rates, ranging from 60.5% to 82.2%, at the lower doses of LHRHa were not significantly different. Mean hatching rates ranging from 30% to 76.5% following induction of sequential spawning by several doses of LHRHa were similar. At all hormone doses tested, mean egg production levels of 37.3–58.7×10 4 eggs/kg body weight were highest on the first day of spawning and declined significantly on subsequent days. Mean egg production levels of 1.2–6.9×10 4 eggs/kg were always lowest on the last day of spawning. Similar egg production levels among all hormone doses during each spawning day were observed. These results indicate that the quality and quantity of spawned eggs may, in part, be influenced by sequential spawnings triggered by LHRHa pellet implantation in sea bass.

Sustained production of milt in rabbitfish, Siganus guttatus Bloch, by weekly injection of luteinizing hormone-releasing hormone analogue (LHRHa)

Abstract Mature male rabbitfish ( Siganus guttatus Bloch) received weekly injections of 200 μ g of luteinizing hormone-releasing hormone analogue (D-Ala 6 , Pro 9 -LHRH-ethylamide) per kg body weight for 5 consecutive weeks. Mean spermatocrit, or packed sperm volume (27–51%), and mean sperm density (3.2–9.6×10 6 spermatozoa per kg body weight) decreased significantly 24 h after each injection. The amount of expressible milt (mean: 5.8–11.7 ml per kg) in response to weekly injections of LHRHa increased significantly relative to saline-injected fish (1.0–2.9 ml per kg), but only during the initial 4 weeks of regular hormone treatment. Three weekly injections of LHRHa likewise augmented mean sperm production (29.2–112.5×10 9 spermatozoa per kg) in rabbitfish. However, no significant enhancement in sperm production by LHRHa-injected fish was observed over the last 2 weeks of hormone injection. These results demonstrate that weekly injection of LHRHa can sustain milt production in mature rabbitfish, although their capacity to produce spermatozoa is limited to only 3 consecutive weeks of regular hormone treatment.

Spermiation response of mature rabbitfish, Siganus guttatus Bloch, to luteinizing hormone-releasing hormone analogue (LHRHa) injection

Abstract A method to quantify the spermiation response of mature rabbitfish to hormonal therapy is described. Spermatocrit or packed sperm volume was measured after milt loaded in non-heparinized microhematocrit capillary tubes was centrifuged for 45 min at 15 000 × g . Sperm density was estimated by a standard hemacytometer method. However, sperm density can be predicted from spermatocrit since their relationship is highly and positively correlated ( Y = 29.5 + 2.95 X r = 0.83; P 6 , Pro 9 -LHRH-ethylamide) per kg body weight and coincided with iow spermatocrit (68%) and sperm density (14.1 × 10 6 spermatozoa per μl milt) levels. These results demonstrate that spermiation in mature rabbitfish can be reliably assessed by a spermatocrit method and that LHRHa can effectively stimulate spermiation in this species.

Development of an ovarian biopsy technique in the sea bass, Lates calcarifer (Bloch)

Abstract A convenient and rapid biopsy method for taking ovarian samples from mature sea bass (Lates calcarifer Bloch) is described. Intra-ovarian oocytes siphoned with polyethylene tubing from any region of the ovary provide a sample representative of the maturational stage of sea bass. The osmolality of a 5% phosphate buffered formalin solution is similar to that of sea bass plasma. The follicular diameter of cannulated sea bass oocytes can be measured within an hour after fixation in 5% phosphate buffered formalin without significantly deviating from the diameter of fresh oocytes.

Advancement of sexual maturation and spawning of sea bass, Lates calcarifer (Bloch), using pelleted luteinizing hormone-releasing hormone analogue and 17α-methyltestosterone

Abstract The ability of luteinizing hormone-releasing hormone analogue [(D-Ala 6 ,Pro 9 -NEt)LHRH], 17 α -methyltestosterone (MT), and their combination to advance gonadal maturation and spawning in captive sea bass ( Lates calcarifer Bloch) broodstock was tested. Several hormonal therapies were tested including monthly implantations of a low dose (100 μg/kg body weight) of each hormone and a high dose (200 μg/kg) implanted to sexually-quiescent sea bass at 45-day intervals. A high dose of LHRHa alone or in combination with MT induced a significant number of mature females (43–71%) in April, 45 days after a single implantation in early March. A lower dose of pelleted LHRHa and LHRHa plus MT was found effective (78–80%) only in May following three monthly implantations. Two and three monthly implantations of a low dose of MT failed to stimulate oocyte growth in April and May whereas a less frequent mode of application of a high dose of the androgen inhibited ovarian growth in April only. A low dose of MT alone significantly increased the number of mature males in April (90%) and May (100%) after two and three monthly implantations. All male sea bass which received three monthly implantations of a low dose of LHRHa and LHRHa plus MT were sexually mature in May. Sexually mature sea bass obtained from these experiments spawned in early May after a single intramuscular injection of LHRHa. These results demonstrate the potential use of pelleted LHRHa and MT to significantly advance gonadal development and spawning in sea bass earlier than the annual breeding season.

A collecting gear for naturally-spawned milkfish (Chanos chanos Forsskal) eggs in circular floating net cages

Abstract A collecting gear for naturally-spawned milkfish ( Chanos chanos Forsskal) eggs in circular floating net cages is described. The gear has been shown to be effective in collecting large numbers of eggs. The collecting gear can be adopted for other broodstock fish species held in circular floating net cages.

Critical factors influencing survival and hatching of milkfish (Chanos chanos Forsskal) eggs during simulated transport

Abstract The effects of loading density, length of transit time, temperature and salinity on milkfish ( Chanos chanos Forsskal) eggs during simulated transport were examined. Rocking motion approximating conditions of transport of eggs collected from milkfish broodstock floating net cages to a hatchery was simulated using a laboratory orbit shaker. Loading densities of more than 7000 eggs/l in shipping bags resulted in decreased rates of survival and correspondingly lower hatching rates. Prolonged shaking simulating extended periods of egg transport also resulted in low egg survival and hatching rates compared to fertilized eggs not subjected to simulated transport. Egg survival after simulated transport at 20°C was lower than at 28°C, except at 20 ppt salinity, where survival was equal. Egg survival at 20°C progressively increased with declining salinity levels whereas high egg survival rates were observed after 2 h of simulated egg transport at 28°C and at the three salinities tested. Hatching rates of fertilized eggs after simulated transport were higher at 28°C than at 20°C regardless of salinity. Neither salinity nor its interaction with temperature affected hatching rates of eggs after simulated transport. These results indicate that survival and hatching of fertilized milkfish eggs after simulated transport is influenced by loading density, transport time, temperature and, to some degree, the salinity of the water. Based on these results, guidelines for handling and transporting milkfish eggs are given.

Stock Enhancement of Threatened Species in Southeast Asia

Natural populations of global inshore fisheries are coming under heavy pressure, primarily due to overexploitation and habitat degradation. Stock enhancement of hatchery-reared seeds is perceived as an alternative strategy to enhance the regeneration process. The Aquaculture Department of the Southeast Asian Fisheries Development Center in the Philippines has been implementing activities related to stock enhancement of donkeys ear abalone (Haliotis asinina), mud crabs (Scylla spp.), giant clam (Tridacna gigas), and seahorses (Hippocampus spp.). Seed production techniques for abalone including a diet tagging method were established, and juvenile abalone were released and monitored in a marine protected area. Mud crabs conditioned before release had higher recapture rates compared to the non-conditioned crabs, which can be translated to higher survivorship. Giant clams stocked at 8–10 cm shell length have high survival 4 mo after stocking (90%), with initial mortalities occurring within the first few days due to transportation stress. Seed production trials for seahorse have begun.

Larval and early juvenile development of silver therapon, Leiopotherapon plumbeus (Actinopterygii: Perciformes: Terapontidae), reared in mesocosms

This work was supported by SEAFDEC Aquaculture Department under the Study code: Nr-04- F2010B. We express our gratitude to Miss Julie Andrea P. Anano, Mr Nemencio B. Olorvida and the student interns from the Polytechnic University of the Philippines (Santa Mesa, Manila) for their assistance during the study.