than controls. At this time, and for several days 

 after, abnormal embryos were noted. These in- 

 cluded the severely retarded embryos and the 

 optical abnormalities noted earlier. Only one 

 control embryo showed slight microphthalmia. 

 Hatching commenced after 11 days and continued 

 for 9 days, at which time the experiment was 

 terminated. After hatching, lordotic fry were seen 

 in the 10 ppb malathion, 10 ppb Sevin, and 25 ppb 

 DDT groups. These skeletal abnormalities were 

 quite rare, however. 



Eye diameters of hatched fry were measured 

 with an ocular micrometer to see if there were 

 slight reductions in optic size in the apparently 

 normal specimens, but no difference between ex- 

 perimental and control fry was seen. 



The fifth experiment was performed the follow- 

 ing summer using about 100 eggs per dish. Eggs 

 were exposed at late cleavage to DDT at 10, 25, 

 and 100 ppb, Sevin at 10, 25, and 100 ppb, and 

 malathion at 1 and 2.5 ppm. Treated groups were 

 again lower than controls in rate of axis forma- 

 tion and heartbeat initiation. Abnormal embryos 

 were seen in most treated groups (Table 1) and all 

 embryos which exhibited optic malformations 

 also showed retardation, stunting of growth, 

 sparse body pigment, and abnormal cardiac de- 

 velopment in which the heart remained a very 

 thin, feebly beating tube without differentiation 

 of the chambers. There were also embryos with 

 this syndrome in which the eyes appeared nor- 

 mal. Hatching commenced after 12 days, and sev- 

 eral fry with scoliosis were seen in the mala- 

 thion dishes. 



Discussion 



The three insecticides reduced survival of 

 Menidia embryos, although this reduction was 

 not always correlated with the dose and varied in 

 different batches of eggs. The main embryotoxic 

 effect was at early stages, preventing successful 

 axis formation. Of those which formed axes, most 

 went on to establishment of heartbeat. 



Notable optic malformations were observed in 

 embryos exposed to DDT, malathion, and Sevin. 

 These three insecticides are quite different from 

 each other chemically, and the fact that they all 

 produced similar malformations may indicate 

 that this species has a propensity toward this 

 type of malformation and various agents can in- 

 voke them. This propensity is supported by the 

 presence of one control embryo with slight mi- 



crophthalmia in one eye. McEwan et al. (1949) 

 likewise concluded that the jewelfish, Hemi- 

 chromis bimaculata, had a tendency to vary ab- 

 normally in certain directions and that an ab- 

 normal environment accentuated this tendency. 

 The most common optic abnormalities seen in our 

 fish were unilateral anophthalmia and microph- 

 thalmia. True cases of cyclopia were rare, though 

 several embryos showed partial convergence of 

 the eye cups, with optic cups directed somewhat 

 ventrally rather than laterally. 



Stockard (1907) produced cyclopia in Fundulus 

 embryos by treatment with MgCl2. In another 

 study (1910) he produced cyclopean, anophthal- 

 mic, and monophthalmic Fundulus embryos after 

 treatment with alcohol, results similar to those in 

 the present study. 



Histological examination of our material re- 

 vealed a case in which the optic cup had partly 

 formed, but appeared to be facing inward rather 

 than outward and had lost its connection to the 

 brain. No lens was present in this specimen. 

 Smithberg (1962) found that tolbutamide caused 

 eye malformations in the medaka, Oryzias 

 latipes. However, these malformations involved 

 degeneration of the eye cup after the lens had 

 been formed, and lenses were present in all the 

 abnormal embryos. These malformations were 

 accompanied by circulatory defects, which he 

 considered responsible for the eye defects. 



Retardation of development was seen by Battle 

 and Hisaoka ( 1952) in their studies of effects of 

 ethyl carbamate (urethan) on embryos of the 

 zebrafish, Brachydanio rerio. Some of their em- 

 bryos also exhibited optical malformations in- 

 cluding anophthalmia, microphthalmia, and 

 cyclopia. In Hisaoka's subsequent study (1958) of 

 2-acetylaminofluorene on zebrafish embryos, 

 microphthalmia was one abnormality produced 

 by this carcinogen. The antibiotic chloram- 

 phenicol was found by Anderson and Battle 

 (1967) to cause a variety of teratogenic effects in 

 zebrafish, including cyclopia and intermediate 

 stages leading to this condition. Colchicine was 

 likewise found by Waterman (1940) to cause a 

 variety of anomalies in the medaka, including 

 cyclopia. 



Aside from general retardation, the optic mal- 

 formations were the major teratological effect of 

 the insecticides on Menidia the first year. 

 Skeletal malformations were also noted but they 

 were relatively rare. In the following year, a vari- 

 ety of malformations in addition to the optic ab- 



210 



