Part 7. Normal histology and histopathology and benthic invertebrates and demersal and platform-associated pelagic fishes

Abstract

"This work was part of a multidisciplinary project which also included studies of hydrography, hydrocarbons, sedimentology, trace metals, microbiology, benthic biology, and biofouling. At least six tissues (muscle, liver, stomach, gonad, excretory/kidney, gill) were examined for histopathological conditions in three species of benthic invertebrates, one species each of bivalves, shrimps, and crabs, and two species of demersal or platform-associated pelagic fishesfrom each site. Specimens were collected from 20 production platforms and four control sites in the north-central Gulf of Mexico. The objectives were to describe pathological conditions and to ascertain any correlation with the proximity of specimens to production platforms. Among invertebrates, the most commonly observed histopathological conditions were protozoan and metazoan symbioses. Other common lesions included inflammation, focal and general leukocytoses, degeneration, necroses, and pigment accumulation. Much variation occurred in the invertebrate species which were available because of depleted bottom populations. At 10 of the 24 sites, including three of the four control sites, either no benthic organisms were present or those that were collected were severely stressed by the low oxygen conditions. Low oxygen conditions were apparently related to the influence of the Mississippi River. Because of the overriding effect of the "dead bottom," valid conelations of the invertebrate pathology with production platforms could not be made.

The following conditions were observed in all six vertebrate tissues: protozoa, helminths, and acidophilic granular cells. Less frequent observations included hyperplasia of the gill filaments, vasocongestion (gill), edema (gill), leukocytosis (liver, gill), fatty infiltration (liver), and chromatophores (liver, kidney, stomach). Much variation occurred between sites in the vertebrate species which were available because of differences in species associated with platforms and those associated with the control areas which did not have a platform. However, a correlation is shown by a comparison of study sites with the total number of histopathotogical conditions found in the fish from the sites.

Three platform sites strongly implicated as contaminated by hydrocarbons and/or trace metals occurred among the top six in total number of histopathological conditions. All eight of the platform sites which ranked high in histopathological conditions were located in the eastern part of the study area and had spadefish as one of the species sampled. Two of these eight platform sites ranked low in effects of hydrocarbons and were "probably not" affected by trace metals.

The four control sites occurred among the bottom seven in number of histopathological conditions. All four ranked medium in effects of hydrocarbons and were "possibly" affected by trace metals. Three were located in the eastern and one in the western part of the study area. Spadefish were not among the species sampled. Two platform sites which occurred among the bottom four in number of histopathological conditions ranked high in effects of hydrocarbons. One, "probably" affected by trace metals, was located in the eastern part of the study area and one, "possibly" affected by trace metals, was located in the western part of the study area. All the sites in the western part of the study area ranked either medium or low in number of conditions. This suggests that the platforms in the eastern part of the study area which consistently show contamination, whether from production or other sources, are those locations where stress is greatest on fish. Conversely, the supposedly least stressed sites show the fewest histopathological conditions."