Clyde S. Tamaru

Technique for making chronic-release LHRH-a and 17α-methyltestosterone pellets for intramuscular implantation in fishes

Abstract Interest in stimulating vitellogenesis in commercially important fishes has led to the use of implantable chronic-release cholesterol pellets and silastic capsules containing LHRH-a and 17α-methyltestosterone, respectively. A detailed description of how these implants are made is provided.

Induced spawning of grey mullet (Mugil cephalus) by LHRH-a

Abstract The application of a high potency synthetic analogue of luteinizing hormone-releasing hormone (LHRH-a), des Gly10 [D-Ala6] LHRH ethylamide for inducing the final stages of maturation and spawning in the grey mullet was investigated. Two LHRH-a injection strategies were used. The first involved the use of carp pituitary homogenate (CPH) as a priming injection for females with average egg diameters of 600 μm or more. This injection was followed, 24 h later, by a resolving injection of LHRH-a. The second stragegy followed the same time frame but LHRH-a was used exclusively for both priming and resolving injections. A high spawning success rate (94.1%) was achieved utilizing the first strategy. Fertilization rates, hatching rates, and qualitative changes in egg morphology were similar to those reported using traditional methods. In this study, 20 mg/kg CPH followed by 200 μg/kg LHRH-a were the minimum dosages that resulted in fertilized spawns. This is the most cost-effective method developed to date for inducing grey mullet to spawn. A 68.4% success rate was achieved when utilizing the second strategy. The minimum total dosage that resulted in fertilized spawns was between 300 and 400 μg/kg LHRH-a. One-third of the total dosage was administered in the priming dose followed by the remaining two-thirds in the resolving injection.

Induced spawning of milkfish, Chanos chanos, by a single application of LHRH-analogue

Abstract Current procedures for induced spawning in milkfish, Chanos chanos , involve the injection of pituitary homogenate and human chorionic gonadotropin followed by hand stripping of the hydrated eggs. This procedure results in the loss of valuable broodstock, low fertilization rates and unpredictable time of spawning. A reliable method for inducing spawning is essential. In this study, luteinizing hormone-releasing hormone analogue (LHRH-a) was tested for its effectiveness as an ovulatory and spawning agent. A single administration of LHRH-a via pellet implantation or liquid injection induced spontaneous spawning approximately 48 or 24 h after application, respectively. The average dosage used was 41.7 ± 3.3 μg/kg body weight for pellet implant and 58.7 ± 9.3 μg/kg body weight for injection. The spontaneous release of eggs was achieved in all spawning attempts when the initial egg diameter was at least 800 μm on average and had a single mode distribution. Seven of 15 attempts with natural fertilized spawns were successful and resulted in an average of 83.8% fertilization.

The paradox of using background phytoplankton during the larval culture of striped mullet, Mugil cephalus L.

Abstract The role of the microalga Nannochloropsis oculata in the rearing of striped mullet ( Mugil cephalus ) larvae was investigated during the first 15 days posthatching. Striped mullet larvae at a density of 20 larvae l −1 were initially provided with rotifers at a density of 10–20 rotifers ml −1 . Rearing took place in two sets of six 30-l tanks that differed only in the addition of phytoplankton (500 000 cells ml −1 ) to one set of tanks. No significant differences in temperature, pH, salinity or dissolved oxygen (DO) were detected between treatments. Un-ionized ammonia (NH 3 ), however, was found to be significantly higher in the tanks stocked with background phytoplankton (range 0.02–0.13 mg l −1 ) as opposed to those that were not ( −1 ). A significant improvement in both larval survival and growth was consistently observed during two independent rearing trials when larvae were reared in the presence of background phytoplankton. The results demonstrate the importance of background phytoplankton during the rearing of striped mullet larvae.

INDUCED MATURATION AND SPAWNING OF MILKFISH, CHANOS CHANOS FORSSKAL, BY HORMONE IMPLANTATION

Abstract The milkfish, Chanos chanos Forsskal, does not reach gonadal maturity easily in captivity. In an attempt to induce maturation, exogenous hormones, LHRH-A and 17α-methyl-testosterone, were implanted into adult milkfish either alone or in combination. The hormones were delivered using cholesterol pellets (LHRH-A) or silastic tubing sealed with elastomer (17α-methyl-testosterone). The fish were implanted three times at monthly intervals between March and May of 1985. The combination of LHRH-A and 17α-methyl-testosterone induced significantly more maturing fish ( P Fish with average egg diameters between 768 μm and 905 μm, spawned 48 h after hormone implantation. These results indicate that the maturation and spawning of milkfish in tanks can be induced and accelerated 1–2 months earlier than the beginning of the normal spawning season through hormone implantation.

Fatty acid and amino acid profiles of spawned eggs of striped mullet, Mugil cephalus L.

Abstract Striped mullet, Mugil cephalus , females were matured in a variety of facilities (i.e., outdoor ponds with seawater or brackishwater, and indoor seawater tanks). Hormonally induced spawnings ( n = 29) resulted in no significant difference in the average spawned egg diameters and fecundity per spawn from females maturing in the various maturation facilities. A significant difference in the percentages of fertilized eggs was obtained from females maturing in the indoor tanks resulting in the lowest average fertilization (50.0 ± 38.6%). In contrast, spawnings from females maturing in the brackishwater pond resulted in an average fertilization of 78.4 ± 28.8%. Fatty acid and amino acid profiles were obtained from the induced spawnings of the striped mullet. No detectable differences were found in the essential or nonessential amino acids and total protein of the spawned eggs. Oleic, eicosenoic, and arachidonic acids were significantly different between the spawned eggs from females maturing in the various facilities.

Factors affecting intensive larval rearing of striped mullet, Mugil cephalus

Abstract Experiments were conducted on larvae of Mugil cephalus to determine onset of feeding, temporal changes in food selectivity, initial stocking density of larvae, rotifers and phytoplankton, and the effectiveness of enriching food organisms. Larvae were observed to possess rotifers in their gut at 70 h posthatch. A significant ( P Artemia resulted in significantly higher growth ( P Artemia or rotifers. Initial larval stocking densities were inversely correlated with survival ( r = −0.58, P 3 cells/ml.

Enhancing the resistance to physical stress in larvae of Mugil cephalus by the feeding of enriched Artemia nauplii

Abstract Striped mullet, Mugil cephalus , larvae were first reared exclusively on rotifers until 15 days post-hatching. Larvae were then separated and reared until 35 days post-hatching using four different rearing strategies: Treatment 1 = newly hatched Artemia nauplii, Treatment 2 = rotifers plus nauplii, Treatment 3 = enriched nauplii, and Treatment 4 = rotifers plus enriched nauplii. No obvious differences in larval growth and survival were observed between treatments. However, significant differences in the ability to tolerate physical handling were observed. Highest mortalities occurred with larvae reared using Treatment 1. Intermediate percentages of mortality were observed from larvae grown using Treatment 2 and almost no mortalities were observed when employing enriched nauplii (i.e., Treatments 3 and 4).

The effect of salinity on the induction of spawning and fertilization in the striped mullet, Mugil cephalus

Abstract Induced spawning was carried out in both 100% seawater (32–34‰) and 50% seawater (15–17‰). Spawning was induced at both salinities, suggesting that final maturation and ovulation can take place across the salinities tested (15–34‰). However, the number of fertilized eggs obtained was significantly lower in the spawning conducted at 50% seawater. Initiation of sperm motility was also found to vary in response to variations in salinity. No motility could be initiated in salinities below 13.8‰, initiation of motility was variable between 14–17‰ and above 17‰ motility was consistently induced. In addition, initiation of sperm motility was determined to be in response to a change in osmolality and not in response to changes in specific ions. From the results of the current investigation, a supply of 100% seawater is recommended for use during the spawning phase of the hatchery production of striped mullet.

Influence of chronic administration of LHRH-analogue and/or 17α-methyltestosterone on maturation in milkfish, Chanos chanos

Abstract Five chronic hormone therapies; cholesterol pellets containing 200 μg of LHRH-a (LHRH-a pellet); silastic tubing packed with either 250μg of dissolved 17α-methyltestosterone (liquid 17α-MT capsule) or 10 mg crystalline 17α-methyltestosterone (crystalline 17α-MT capsule); or the combinations of LHRH-a pellets plus a liquid 17α-MT capsule or LHRH-a pellets plus a crystalline 17α-MT capsule, were tested to determine the best treatment for inducing maturation in captive milkfish ( Chanos chanos ). Experimental groups of 20 milkfish each received one of these five therapies. A sixth control group received placebo implants. LHRH-a pellets were administered monthly; crystalline 17α-MT capsules were administered once, and liquid 17α-MT capsules were administered twice, at the beginning of the experiment and 3 months later. Results show that the combination of LHRH-a pellets plus liquid 17α-MT capsules in the most effective hormone therapy for enhancing the maturation of both sexes. Fifty percent of these fish matured in April, 1 month after implantation, and close to 90% of the fish in this treatment matured by July. The combination of LHRH-a pellets plus crystalline 17α-MT capsules enhanced the maturation of male milkfish but not female. LHRH-a alone was also effective in the maturation of females, but was the least effective of all treatments in maturing males. 17α-MT capsules alone, in either form, did not induce maturation in female milkfish.