Role of sea surface temperature and rainfall in determining the stock and fishery of the common octopus (Octopus vulgaris,Mollusca, Cephalopoda) in Tunisia

Octopus (Octopus vulgaris, Mollusca, Cephalopoda) is an important and valuable fishery resource on the eastern and southern coasts of Tunisia, but its landings are highly variable. This paper explores the effect of environment on octopus catch per unit effort (CPUE) during a 12‐year period, through correlation analyses and the incorporation into surplus production models of sea surface temperature (SST) and rainfall data collected during cold (January–May) and hot (August–October) seasons. CLIMPROD software was used to select the appropriate model and fit it to the fishery and environment data. In both seasons, SST significantly contributed to CPUE variability; fishery production was influenced positively by cold season SST but negatively by hot season SST. Due to a poor fit with cold season data, the impact of rainfall was analysed only for the hot season, during which it has a positive effect on production. Results are discussed in view of the life‐cycle of octopus and the dynamics of the Tunisian fishery. This first study of octopus variability in Tunisia highlights the necessity to incorporate environmental influence into stock assessment and management advice.     

Double-layer disk and magnetic field dynamics in the Crab Nebula

The mechanism of the large-scale magnetic field generation in the Crab Nebula is proposed. The basis for the considered fast mechanism is the model of the central region of Crab Nebula amorphous part having the form of slightly divergent double-layer disk consisting of the relativistic electron-positron plasma.The nebula toroidal magnetic field generation occurs in the double-layer disk in the immediate neighbourhood of the light cylinder of pulsar PSR 0531+21 due to the differential rotation by means of dynamo-mechanism. The generated field is transferred into the nebula by the pulsar wind which forms the double-layer disk.By use of the known parameters of pulsar PSR 0531+21, the considered mechanism yields the strength of magnetic fieldB=10^–3 G observed in the nebula. The disk structure must be destroyed toward the edges of the nebula.     

Using of the Ornamental Fish in Wastewater Biological Treatment

Breeding ornamental fish in wastewater was a successful solution not only to decrease sanitary risks but also to encourage fish growth. In fact, the secondary treated effluent was used to grow a walking catfish (Clarias batrachus), a western mosquitofish (Gambusia affinis; Poeciliidae), and a leopard pleco (Glyptoperichthys gibbiceps). The growth rate of fish reared in final treated wastewater was significantly higher than of treated effluent (25 and 50%) and the relative growth rate during 2 months reached 2, 4, and 2.5, respectively. Bacterial loads were important in the gills compared to other fish organs (intestine, skin, and edible muscles). However, the total aerobic germs ranged between 2 × 10³ and 3.4 × 10³ cfu/g in the edible fish species cultured in secondary treated effluent. The pathogenic bacteria Aeromonas hydrophila was absent in all examined fish muscles. However, the presence of tested fishes did not prevent the reduction of the treatment biological parameter (BOD and COD) at half, in the three treated wastewater proportions (25, 50, and 100%) and thereafter, they clearly participated to the tertiary biological treatment of used water. Further bacteriological and physico‐chemical analyses indicated that the use of treated wastewater in aquaculture is safe and risks to human health are reduced.     

RECENT UNDERTHRUSTS OF TIANSHAN AND POSSIBLE MECHANISM OF THEIR ORIGIN

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