family were almost exclusively killed, particularly 

 the commercially important Cynoscion squamipin- 

 nis. Mortalities appeared to decline by late October, 

 and after 4 November, no sciaenid mortalities were 

 reported. 



Six fish collections were made between 12 Octo- 

 ber and 4 November 1985 in the vicinity of Punta 

 Morales, by following flotsam windrows in a skiff 

 and indiscriminately collecting fishes from the water 

 surface with a landing net. Collections lasted from 

 1 to 2 hours, and the fishes were subsequently sent 

 to the laboratory and identified. 



Fishes taken in the collections were almost entire- 

 ly (98%) sciaenids, including 15 sciaenid species from 

 7 genera (Table 1). Affected sciaenids ranged in size 

 from 46 to 490 mm SL. Species observed in the mor- 

 tality, but not taken in the quantitative collections, 

 included Anchovia macrolepidota, Oligoplites sp., 

 Chaetodipterits zonatxis, Sphoeroides tricocephalus, 

 and the sciaenid Cynoscion stolzmanni. 



Nearly all fishes were dead upon collection, with 

 few moribund individuals observed. Dead fishes 

 were generally found floating belly-up, while the 

 moribund ones often were floating motionless and 

 taking slow, intermittent breaths. No lacerations or 

 other obvious external marks were noticeable at the 

 time of collection, and most of the fishes appeared 

 fresh. Digestive tracts of several examined speci- 



Table 1— Fish species taken in periodic collections during fish 

 mortality in the Gulf of Nicoya, 12 October-4 November 1985. Data 

 pooled for six collections. 



mens were empty. Some of the larger species were 

 collected by local fishermen and eaten or sold for 

 food, with no apparent deleterious effects. 



Four moribund sciaenids (3 Cynoscion squamipin- 

 nis, 1 Ophioscion sciera) and a puffer (Sphoeroides 

 tricocephalus) were collected and preserved in 10% 

 buffered formalin (pH 7.2), and the internal organs 

 were sectioned and stained using standard histo- 

 logical methods. Control sections were made from 

 C. squamipinnis and C. phoxocephalus collected 

 several months after the mortality. Major macro- 

 scopic abnprmalities in all specimens included 



1) Presence of petequial hemorrhages in the oral 

 cavity, gill arches, operculum, and base of the 

 pectoral fins. 



2) Destruction of the distal third and hyperemia in 

 the proximal two-thirds of the secondary gill 

 lamellae. 



3) Presence of blood and blood clots between the 

 two layers of the pericardium. 



4) Pronounced paleness of the liver, very crumbly 

 upon cutting. 



5) Congestion and hemorrhages in the intestinal 

 serosa. Fibrous bands adhering some segments 

 of the intestinal serosa to the abdominal wall. 



6) Kidney and spleen crumbly and of a semiliquid 

 consistency. 



7) Gastrointestinal system containing a yellow- 

 green mucous. 



Major microscopic findings included 



1) Large numbers of eosinophilic granulocytic cells 

 in the submucosa of the gastrointestinal system, 

 apparently in response to a high load of nema- 

 tode and intermediate stage cestode parasites 

 encysted in the layers of those organs. Intense 

 development of connective tissue around the per- 

 ipheries of those parasites. 



2) Necrosis of haemopoietic tissue of the spleen with 

 the proliferation of melanomacrophage centers. 



3) Generalized vacuolar degeneration of the hepatic 

 parenchyma with areas of extensive necrosis. 



4) Necrosis of renal hematopoietic tissue and degen- 

 eration of the renal tubule epithelium (nephrosis). 



The combination of tissue irregularities observed 

 is compatible with pollutant-induced damage (King 

 1962; Buhler et al. 1969; Walsh and Ribelin 1975), 

 but we have no direct evidence linking pollution 

 to the mortality. We suspect that an agricultural 

 toxin may be involved because a large number of 

 agrochemicals are currently in rather indiscriminate 



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