ALBERT

Notes: Based on egg collection records, spontaneous spawning activity of sea bass, Lates calcarifer (Bloch), reared in floating net cages followed a semilunar cycle. The peak of multiple spawnings coincided with declining spring tides of quarter moon periods. Maximum diameter of intra-ovarian, ripe oocytes (0.51–0.55 mm) occurred in synchrony with the quarter moon periods. Smaller oocytes (0.44–0.47 mm) were sampled during the new and full moon periods. Two structural analogues of luteinizing hormone-releasing hormone (LHRHa) (des-Gly10, d-Ala6-LHRH ethylamide and d-Ala6, Pro9-Nethylamide-LHRH), in pelleted or dissolved form, induced mature female sea bass with a mean egg diameter of at least 0.40 mm to spawn at any day during the lunar cycle. The onset of spontaneous and LHRHa-induced spawnings occurred during low tides in the evening until dawn (from 19.00 to 05.00 hours). These results demonstrate that LHRHa can effectively induce mature sea bass to spawn independent of the highly predictable semilunar spawning rhythm. In addition, the occurrence of both spontaneous and hormone-induced spawnings at a precise period of the day suggest a tidal and diurnal cue entraining spawning of mature female sea bass.

Notes: The effect of various doses of luteinizing hormone-releasing hormone analogue (LHRHa) ranging from 1 to 100 μg/kg body weight on the spawning response of mature female sea bass, Lates calcarifer (Bloch) was tested. A single intramuscular injection of LHRHa resulted in a dose-related increase in the spawning rate (number of spawnings of each fish over four consecutive days) of mature fish. An LHRHa dose of 5 μg/kg and less induced low spawning rates of 16.7% to 37.5% or at least one spawning every four days. However, mature sea bass spawned more than once (43.8–58.3%) in four days at dose levels of 10 μg/kg and above. Hormone treatment within the dose range tested did not influence the number, fertilization and hatching rates of spawned eggs.The influence of initial oocyte size on the LHRHa-induced spawning response of mature sea bass was also examined. Sea bass with an initial oocyte diameter of 0.30–0.39 mm did not respond to the single injection of 100 μg LHRHa/kg. In contrast, LHRHa induced spawning among sea bass with an initial egg size of 0.40–0.49 mm, although two of four sea bass of the same stage of ovarian maturity spawned spontaneously. Fish having an initial oocyte size of 0.50–0.55 mm spawned with and without LHRHa treatment. Spontaneous spawning among saline-injected sea bass occurred at a later time (24–58 h post-injection) compared to fish induced to spawn by a single injection of LHRHa (8–36 h post-injection). The initial spawning response time interval for fish with an initial egg size of 0.50 mm or greater was further reduced to 8–9 h by LHRHa. These results indicate that LHRHa can successfully induce spawning in mature female sea bass which have attained a critical oocyte diameter and that the spawning response interval is reduced with a further increase in egg size beyond the critical oocyte diameter limit.

Notes: An opercular tag for marking adult milkfish (Chanos chanos Forsskal) and seabass (Lates calcarifer Bloch) is described. High tag retention and relatively low mortality rates were observed in adult fish handled two to ten times during 14-to 60-day tests. The features and advantages of the tag for marking large-sized fish in short-term studies are discussed.〈section xml:id="abs1-2"〉〈title type="main"〉ZusammenfassungEine preiswerte Markierung für Kurzzeitstudien des Milchfisches (Chanos chanos Forsskal) und der Centropomidae (Lates calcarifer Bloch)Eine Kiemendeckel-Markierung für adulte Milchfische (Chanos chanos Forsskal) und Centropomidae (Lates calcacifer Bloch) wird beschrieben. Sie zeichnet sich durch gute Haltbarkeit aus und verursacht relativ geringe Mortalität bei adulten Fischen, die in Versuchen von 14 bis 60 Tage Dauer 2-bis 10mal untersucht wurden. Die Eigenschaften und Vorteile dieser Markierung für große Fische in Kurzzeitstudien werden diskutiert.〈section xml:id="abs1-3"〉〈title type="main"〉RésuméUn marquage économique pour des études de courte durée du chanidé (Chanos chanos Forsskal) et du centropomidé (Lates calcarifer Bloch)Un marquage d'opercule pour les chanidés (Chanos chanos Forsskal) et les centropomidés (Lates calcarifer Bloch) adultes est décrit. Une bonne conservation et une mortalité relativement basse ont été observées chez des poissons adultes examinés 2 à 10 fois pendant des expériences d'une durée de 14 à 60 jours. Les caractéristiques et les avantages du marquage de poissons de grande taille pendant des expériences d'une courte durée sont discutés.

Notes: Mature female sea bass (Lates calcarifer Bloch) were injected once intramuscularly with 20 μg luteinizing hormone-releasing hormone analogue (D-Ala6, Pro9-LHRH-ethylamide) per kg body weight (BW) at different times of the day. Following hormone injection, the incidence of initial spawning and the number of eggs spawned by each fish were recorded. Saline-injected fish did not spawn. Fish spawned at dawn or 33.7–40 h after an LHRHa injection at either 11.00 h or 17.00 h. When LHRHa was administered at 23.00 h or 05.00 h, sea bass spawned during the day or at 38–47.3 h post-injection. Mean egg production levels of 26.8–34.4 × 104 per kg BW were higher for fish which spawned at dawn. Low mean egg production levels (6.2–19.9 × 104 eggs per kg BW) were observed when LHRHa-injected fish spawned during the day. These results demonstrate that the time of initial occurrence of spawning varied with the time of day that LHRHa was administered and that the number of eggs shed was influenced by the time of day that hormone-induced sea bass spawned.〈section xml:id="abs1-2"〉〈title type="main"〉ZusammenfassungVerzögerung der Ablaichreaktion und Kapazität der Eiproduktion von LHRHa-injizierten reifen Seebarschweibchen (Lates calcarifer Bloch)Reife Weibchen des Seebarsches Lates calcarifer Bloch wurden einmalig intramuskulär mit 20 μg des “luteinizing hormone-releasing hormone” Analogons (D-Ala6, Pro9-LHRH-ethylamid) pro kg Körpergewicht zu verschiedenen Taeszeiten injiziert. Nach der Injektion des Hormons wurde die Häufigkeit der erzielten Laichreife unj die Zahl der abgelaichten Eier pro Fisch erfaßt. Salz-injezierte Kontrollfische laichten nicht. Behandelte Fische laichten 34 bis 40 h nach der LHRHa-Behandlung entweder um 11.00 Uhr oder urn 17.00 Uhr. Wenn die LHRHa-Dosis urn 23.00 Uhr oder 05.00 Uhr verabfolgt wurde, laichten die Seebarsche während des Tages oder 38–47 Stunden später. Die mittlere Zahl der abgelaichten Eier betrug 26,8–34,4 × 104 pro kg Fisch und war stets höher für Fische die zur Dämmerungszeit laichten. Niedrige mittlere Eizahlen (6,2–19,9 × 104 Eier pro kg Körperewicht) wurden enielt wenn die behandelten Fische am Tage laichten. Diese Ergebnisse machen deutlich, daß das Erstlaichen mit der Tageszeit der LHRH-Injection variiert und das die Zahl der Eier von der Tageszeit zu der gelaicht wird, beeinflußt ist.〈section xml:id="abs1-3"〉〈title type="main"〉RésuméRetardement du frai et capacité de production d'oeufs des femelles matures de barramundi (Lates calcarifer Bloch) injecteéspar un analogue du facteur de libération de l'honnone lutéinisanteDes femelles matures du barramundi (Lates calcarifer Bloch) ont été traitées par une injection intramusculaire de 20 μg ar kg de poids de Poisson d'un analogue du facteur de libération de l'hormone lutéinisante (D-Afa6, Pro9-LHRH-ethylamide) sà differentes heures de la journée. Après l'injection, l'incidence initiale du frai et le nombre d'oeufs frayés par poissons ont été mésurés. Les poissons injectés avec de l'eau saline ne frayaient pas. Les poissons frayaient au crépuscule ou 33.7–40 heures aprés une injection de LHRHa sà 11.00 ou 17.00 heures. Quand le LHRAa a été administré sà 23.00 ou 5.00 heures, les barramundis frayaient pendant la journée ou 38–47.3 heures après l'injection. Le taux moyen de production d'oeufs (26.8–34.4 × 104 oeufs par kg de oids de poissons) étair plus élevé pour les poissons qui frayaient au crépuscule. Les taux moyen de production d'oeufs étaient bas (6.2–19.9 × 104les oeufs par kg de poids de poissons) quand les poissons injectés au LHRHa frayaient pendant la journée. Les résultats montrent que le moment initial du frai initial a varié avec l'heure du jour sà laquelle le LHRHa a été administré et que le nombre d'oeufs frayés est influencé par l'heure du jour sà laquelle les barramundis stimulé par l'hormone frayaient.

Notes: The spawning induction activity of dissolved and pelleted (D-Ala6, Pro9 N ethylamide) luteinizing hormone-releasing hormone analogue (LHRHa) stored for various periods was assessed in mature female sea bass. The spawning response of mature fish was reduced significantly after injection of dissolved LHRHa (20 μg kg−1) stored for more than 90 days in a refrigerator (4–10°C) or for more than 30 days at room temperature (28–30°C). Similar to fish administered fresh preparations of LHRHa, fish spawned successfully after injection of a solution of LHRHa previously frozen, subjected to alternate freezing and thawing, exposed to sunlight or implanted pelleted LHRHa (50 ng kg−1) stored at room temperature for 30–120 days. Loss of hormone bioactivity after prolonged storage may have been due to bacterial growth in solubilized preparations. Injection or implantation of stored LHRHa did not influence egg production among treated sea bass. These results demonstrated the relatively prolonged shelf life of stored LHRHa.