Toxicity of malathion at early life stages of the Senegalese sole, Solea senegalensis (Kaup, 1858): Notochord and somatic disruptions

The toxicity of malathion to Solea senegalensis was studied in a static renewal bioassay for 24, 48 and 72 h, with toxicant concentrations ranging from 1.56 until 100 µgL-1. The LC50 values of malathion for 48 and 72-h was 63.5 (95% C.I: 50.83-79.34) and 22.94 (95% C.I: 17.16-30.68) µgL-1 respectively. The survival of larvae was non-affected by exposure to malathion at concentrations up to 25 µgL-1 (24 h NOEC), 6.25 µgL-1 (48 h NOEC) and <1.6 µgL-1 (72 h NOEC). At the end of the experiment, surviving larvae from concentrations smaller than the 72h-LC50 were chosen to study morphological changes during malathion exposure. Results revealed a strong disruption in the notochord and trunk musculature integrity as a result of toxicant exposure. Noticeable changes in the composition and reduction of collagen fibers from the perinotochordal connective sheath and perimysium were clearly detected. The trunk musculature was also altered, showing a general disorganization of fibers. Moreover, malathion exposure provoked pericardial and yolk-sac oedemas and histopathological alterations in some other organ- systems and tissues (i.e. liver, pancreas, intestine).