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Laboratory experiments wer conducted to determine the effects of Kepone on the larval development of the mud-crab,Rhithropanopeus harrisii, and the commercial blue crab,Callinectes sapidus, from the time of hatching until the 1st crab stage was reached.

Survival of Rhithropanopeus harrisii larvae from hatching to first crab stage occurred in Na2CrO4 concentrations from 1.1 to 29.1 ppm. Estimated LC50 for complete zoeal development was 17.8 ppm Na2CrO4 and it was 13.7 ppm for development to first crab stage. A concentration of 1.1 ppm Na2CrO4 was nontoxic, while Na2CrO4 concentrations of 7.2 and 14.5 ppm were sublethal and concentrations of 29.1 to 58.1 ppm were acutely toxic. Low concentrations of Na2Cr04 caused an increase in swimming speed and high concentrations caused a decline.

Laboratory experiments were conducted to determine the effects of methoxychlor on the larval development of the mud-crab, Rhithropanopeus harrisii, and the commercial blue crab, Callinectes sapidus, from the time of hatching until the 1st crab stage was reached. The effect of a range of concentrations of methoxychlor on survival of larvae of C. sapidus and R. harrisii was determined, as well as the concentrations which were sublethal and lethal. Since concentrations as low as 1.3, 1.6 and 1.9 ppb (μg l−1) methoxychlor were acutely toxic to C. sapidus larvae, and it took a concentration as high as 7.0 ppb to be acutely toxic to R. harrisii larvae, it was concluded that C. sapidus larvae were much more sensitive to methoxychlor than R. harrisii larvae. Zoeal and total development to the 1st crab stage of R. harrisii and C. sapidus were prolonged in relation to increased concentrations of methoxychlor. The developmental stages in which larvae were particularly sensitive varied in the two species. Methoxychlor residues of R. harrisii and C. sapidus larvae reared in concentrations of methoxychlor were determined.

The mud aqueous fraction (MAF) and suspended particulate phase (SPP) of low-density lignosulfonate type mud with uerrochrome added were nontoxic to larvae during the complete larval development of Rhithropanopeus harrisii. Five percent (5000 ppm, 0.5 % v/v mud in water) MAF and SPP were not toxic to Callinectes sapidus. Survival of C. sapidus larvae decreased as concentrations of MAF and SPP increased from 5 % (5000 ppm, 0.5 v/v mud in water) to 50% (50000 ppm, 5 % v/v mud in water). No larvae reached the 1st crab stage in 100% (100000 ppm, 10% v/v mud in water) MAF and SPP. Statistical analysis of the data on survival, mortality, and behavior are presented.