Regarding fish spoilage microbiology, the bacteria most often implicated are typically derived from which source(s)?

Introduction:
Fresh fish carry abundant psychrotrophic and psychrophilic bacteria on their skin mucus (slime) and in the gastrointestinal tract. This question checks whether you recognize the primary origin of organisms that later drive spoilage during storage.

Given Data / Assumptions:

• Harvest and handling transfer microbes from skin and gut to flesh and work surfaces.
• Chilling slows, but does not stop, growth of many spoilage bacteria.
• Good hygiene reduces but cannot eliminate the natural flora introduced pre-harvest.

Concept / Approach:
The dominant spoilage flora reflects the fish’s initial microbiota: skin slime and intestinal contents. After death, barriers break down, facilitating spread into tissues. With time at chill temperatures, psychrotrophs (e.g., Pseudomonas, Shewanella) proliferate, producing off-odors, trimethylamine, and slime. Therefore, the correct source is the normal external and intestinal flora, not an undefined “internal slime only.”

Step-by-Step Solution:
Identify pre-existing flora: external mucus and gut contents. Relate post-harvest handling and evisceration to cross-contamination. Connect psychrotrophic outgrowth to spoilage traits. Select the option naming external slime and intestines.

Verification / Alternative check:
Microbiological surveys of fresh catch routinely find high counts on skin/gills and in intestines, matching later spoilage isolates.

Why Other Options Are Wrong:

• Internal slime only: Too narrow; excludes major exterior source.
• Both / None: Do not accurately reflect the typical origins as precisely as option (a).

Common Pitfalls:
Assuming spoilage flora are mainly environmental contaminants; endogenous flora are usually the key contributors.

Final Answer:
part of the natural flora of the external slime of fishes and their intestinal contents most often cause spoilage.