Abstract
Biological fouling organisms on fish cages represent a major issue and costly factor in marine finfish aquaculture. Cnidarians have been identified as one of the most problematical groups, contributing significantly to the occlusion and structural stress of the cage nets, but also dramatically affecting farmed species health in aquaculture facilities worldwide. Recently, significant relationships were established in different Spanish aquaculture facilities between hydrozoans and juvenile fish affected by gill injuries and mortality episodes. Community composition, growth rate and reproductive potential of biofouling were monitored on fish cages over two seasonal periods of fry cages farming, located in southern Spain (SW Alboran Sea), with a special focus on cnidarians. Biomass and community composition of biofouling changed with time and between studied periods, with a marked seasonality in colonization periods and taxonomic composition, particularly for the colonial hydrozoans. The hydroids Ectopleura larynx and Pennaria disticha were found at the highest densities. P. disticha was responsible for major biomass contribution to total hydroid biomass with the fastest growth rates. In addition, actinulae larvae of E. larynx were identified in zooplankton samples at high densities especially during periods of fry introduction in sea cages (when fish are highly vulnerable). These results corroborate evidence of the detrimental influence of fouling cnidarians in Mediterranean finfish aquaculture due to a direct harmful impact on fish health. Investigations on population dynamics, reproductive biology and envenomation potential of fouling hydrozoans should be regarded as key component of best monitoring practices to ensure good farmed fish welfare, maximization of aquaculture production and overall marine spatial planning.
Highlights
Biofouling is a major problem and costly factor in marine finfish aquaculture worldwide
The accumulation of epibiotic organisms can increase the hydrodynamic load on fish nets [1], reducing water flow and oxygen supply, affecting the susceptibility of farmed fish to diseases [2,3]
Hydroids are known as a threat for finfish mariculture due to the contact envenomation and secondary bacterial infections induced on farmed species health [6]
Summary
Biofouling is a major problem and costly factor in marine finfish aquaculture worldwide. The accumulation of epibiotic organisms can increase the hydrodynamic load on fish nets [1], reducing water flow and oxygen supply, affecting the susceptibility of farmed fish to diseases [2,3]. Some polychaete worms excavate the shells of shellfish, affecting their development and increasing their vulnerability to predators and parasites [6]; some tunicates compete with farmed mussels for food [9]; and several hydroids are known to regularly feed on mussel larvae and foul the shells of cultivated mussels, causing significant reduction in bivalve length and weight [7]. The hydroid Ectopleura larynx has become one of the most common fouling species in northern Europe aquaculture, causing increasing problems for fish farmers [11]. Fouling represents a costly and labour-intensive issue for marine fish farmers, a remarkable lack of knowledge still occurs about the structure and seasonal dynamics of the hydroid fouling community
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