Search

The article discusses the study that addresses the possibility of harvesting large quantities of organic particles released by net pen finfish. An experiment was done in the northern Gulf of Aqaba, Red Sea and at a nearby reference site to observe whether the biofouling communities that developed on these were different in terms of biomass, diversity and species richness. The results show that there is merit to make net pen fish farming more environmentally sustainable.

A field study was carried out to assess the use of the bottom-feeding grey mullet ( Mugil cephalus) within benthic enclosures as a means to reduce the benthic impacts of a net cage fish farm in the Gulf of Aqaba, Red Sea. Five experimental 1-m3 net-cage enclosures were stocked with 12 grey mullets each (fish weights 50, 70 or 144 g). The enclosures had no bottom and the mullets had access to the enclosed organically enriched sediments and to particulate matter (PM) falling from the overlying cages. Sediment traps were used to quantify and qualify the PM falling from the fish farm to the sea floor. Simultaneously, a feeding trial was performed with mullets (50 and 70 g) in experimental tanks. In order to estimate the potential growth rate and to quantify energy and protein requirements, the fish were fed a formulated diet with known composition. After approximately 70 days at sea, mullets in the enclosures had used up all the available food in the sediment and gained up to 0.78 g day−1 fish−1. Applying the values for energy and protein requirements for maintenance and growth derived from the experimental trial, estimates indicated that the grey mullets effectively removed 4.2 g organic carbon, 0.70 g nitrogen and 7.5 mg phosphorus kg−1 mullet m−2 day−1 from the organically enriched sediment. Thus deployment of grey mullets may be an efficient means to improve the quality of sediments below intensive net-cage fish farms. [ABSTRACT FROM AUTHOR]

Two artificial reefs made of porous recycled high-density polyethylene fence material were moored on the sea floor (20-m depth) off the North Beach of Eilat (Gulf of Aqaba, Red Sea) in April 1999. One reef was situated below a commercial net-cage fish farm, and a control reef was deployed outside the area of direct influence of the farm. The objective was to determine if a reef below farm cages could alleviate organic loading of the environment by serving as a biological filter. To examine this question in both qualitative and quantitative terms, the two reefs were compared with regard to organic matter in the sediment close by, abundance of fish and invertebrates, particle filtration (retention) efficiency, and change in biomass of fouling organisms. In addition, control sites situated near the two reefs were also monitored to compare the status of the sediment and of associated biota with those of the reefs. The differences in organic matter content of the sediment between each reef and its respective control site were not significant. Also, fish community metrics did not differ significantly, although the total number of fish was 30% higher at the farm site. Biomass of fouling organisms (particularly tunicates and bryozoans) varied inconsistently between sites over time. Particle retention efficiency of the reefs was estimated at 240 g C d−1, based on the reduction in particulate Chl a in water samples taken downstream of the reefs compared with samples taken upstream. Copyright 2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd. All rights reserved. [ABSTRACT FROM PUBLISHER]