High-density Aquaculture Research Articles

AQUACULTURAL EFFLUENTS: DIRECTIVE SIGNALS TO THE SYSTEM DOWNSTREAM?

Animals continuously release biogenic substances that vary in composition with physiological state. In aquatic systems, animals can gain insight about conditions or events upstream and alter their physiology and behavior to exploit this information. Here, we review observations on aquatic animals as diverse as snails, shrimp, fish, and frog tadpoles to probe the possibility that high-density aquaculture might generate chemical messages that cause conspecific or related individuals to reduce productive processes (growth, metamorphosis, ecdysis, reproduction) or even to sicken and die (loss of immunocompetence, anaphylaxis). The potential for ecological disruption logically is maximized under conditions that uncouple the parts of the system generating and receiving such signals—as would be the case when aquacultural effluents enter natural aquatic systems.

Isolation of Aeromonas hydrophila from Oreochromis niloticus during Fish Disease Outbreaks in the Philippines

The study focused on the bacteriological examination of Nile tilapia, Oreochromis niloticus, during fish disease outbreaks in various aquaculture farms and projects in Luzon, Philippines. Farm sites and aquaculture research projects which had outbreaks were visited from January 1994 to February 1996. Fish samples were observed to have disease signs like skin lesions, ulcerations, fin rot, body discoloration, mouth sore, eye opacity, exophthalmia, dislodged eyeball, and sluggishness. High mortalities of Nile tilapia were monitored in cage culture projects notably during the rainy season and cold months. Streaking into plates of nutrient agar, trypticase soy agar and Rimler-Shotts media was done for primary isolation of bacteria. Isolates were obtained from different tissues of diseased Nile tilapia samples such as ulcerated skin and muscle, liver, kidney, spleen, gall bladder and opaque eyes. All isolates had heavy growth of yellow colonies in Rimler-Shotts media. In primary characterization tests, they were gram negative, rod-shaped, motile, oxidase positive, fermentative, 0/129 resistant and novobiocin resistant, suggesting that the colonies were aeromonads. Detailed examination using differential tests and AP! 20E showed the isolates to be Aeromonas hydrophila. All isolates were sensitive to chloramphenicol and oxolinic acid but resistant to ampicillin. Reaction to other antibiotics such as streptomycin, erythromycin and oxytetracycline varied from resistant, intermediate and sensitive. Experimental infection of the disease by immersion route was done and mortalities were monitored for 96 hrs. Results showed LC50 at 1.5 x 106 at 96 h, LC100 at 108, and no mortality at 103 and control. Moribund fish manifested the same clinical signs as the naturally infected Nile tilapia. Consistent isolation of A. hydrophila from various tissues of diseased Nile tilapia during disease outbreaks shows a recurring septicemia. Occurrence of the disease has been observed in low-volume and high-density aquaculture of Nile tilapia during the rainy season and cold months when temperatures are low. Regular disease outbreaks pose a threat to the Nile tilapia industry, necessitating steps to control the disease and minimize economic losses.

Rotatable Cage for High-Density Aquaculture

(1972). Rotatable Cage for High-Density Aquaculture. The Progressive Fish-Culturist: Vol. 34, No. 1, pp. 8-8.