Technology research news Return to previous page
Article Released Mon-7th-August-2006 01:47 GMT
Contact: Madeleine Institution: PCAMRD
 Mangrove Red Snapper Now Bred in Captivity

The mangrove red snapper (Lutjanus argentimaculatus), is an important food fish in Southeast Asia. Several trials were conducted to evaluate the efficacy of hormones to induce spawning of mangrove red snapper.

MANGROVE RED SNAPPER NOW BRED IN CAPTIVITY


The mangrove red snapper (Lutjanus argentimaculatus), is an important food fish in Southeast Asia. It is widely-distributed in the Indo-West Pacific from Samoa and the Line Islands to East Africa, and from Australia northward to Ryukyu Island, Japan. Like groupers (Family Serranidae) and sea bass (Lates calcarifer Block 1790), the mangrove red snapper commands a high market price and is in much demand in Southeast Asia.

While several species of snappers belonging to the Family Lutjanidae have been bred in captivity, fry production is still limited. Through a study conducted by Dr. Arnil C. Emata of the Aquaculture Department, Southeast Asian Fisheries Development Center based at Tigbauan, Iloilo, a reliable means of inducing spawning of cage-reared mangrove red snapper broodstock with high egg production rates and good egg quality was developed to augment the shortage of snapper fry.

Broodstock of mangrove red snapper (five to seven years old) weighing 2.25-4.75 kg body weight from the wild or hatchery-produced fry reared to adults were kept in floating cages. Trash fish was fed to the fish at 5% of their total body weight every other day.

For the induced spawning of the mangrove red snapper, several induction trials were conducted to determine the optimum hormone dose and egg production and quality. The fish were individually removed from the cage and anesthesized with 200-ppm 2-phenoxy-ethanol to obtain body weight and assess gonadal development. Each fish was weighed and distinguished as female or male, depending on the presence of cannulated oocytes or milt after applying gentle pressure on the abdomen. Only females with oocytes with average diameter oocytes of > 0.40 mm (n = 50) and males with milt were considered mature and used for induced spawning. Mature females and males were injected once at the base of the pectoral fin into the peritoneal cavity with human chorionic gonadotropin (HCG) at 500, 1000 or 1500 IU/kg or luteinizing hormone-releasing hormone analogue (LHRHa) at 50 and 100 mg/kg.

In the spontaneous spawning, eggs were checked in the water column of cages from midnight to early morning. A manually-operated sweeper-type egg collector used for milkfish was used to collect the eggs. To prevent the escape of eggs, cages were lined with hapa nets (0.6-0.7 mm). The hapa nets were lifted and cleaned every morning to allow water exchange during the daytime whether spawned eggs were detected or not. The volume and quality of spawned eggs were determined as in the induced spawning trials.

Among the several induced spawning trials conducted, it was noted that the reproductive performance of spawns induced by different treatments did not differ significantly from those obtained from natural spawns.

Results showed that the use of HCG at higher doses (1,000 and 1,500 IU/kg) effectively induced spawning of mangrove red snapper but a lower dosage (500 IU/kg) did not show any signs of spawning. These results are in conformity with those of other lutjanids such as L. griseus and L. analis wherein a dose of 1,000 IU/kg HCG has been used to induce spawning successfully.

Induced spawning of lutjanids with the use of LHRHa is rare. According to Dr. Emata, it was used only in his previous study and this study. It was also noted in other studies where LHRHa was used to induce L. johnii to spawn, it was administered as implants in pellet form. The present study also conformed with that mode of administering LHRHa through implants. Thus, the results suggest that to induce spawning in lutjanids, HCG is effective by injection while LHRHa is effective by injection and implants.
The mangrove red snapper is a highly fecund fish. It was noted that the female L. argentimaculatus can produce an average of about one million eggs per spawn following induced or natural spawning. In the study, it was found that a single dose of LHRHa at 100 mg/kg or HCG at 1,000 and 1,500 IU/kg can effectively induce mangrove red snapper to spawn.



Keywords associated to this article: mangrove red snapper, spawning, induce
Create Account...