Fish Fillet Identification and Postmortem Interval

The discussion focuses on the identification of fish fillets, particularly in the context of wildlife conservation and combating fish mislabeling.
Emphasizes the importance of understanding fish identification as it relates to law enforcement in wildlife crime investigations.

Mislabeling is a common occurrence in wildlife crime and is crucial today. - Mislabeling can lead to legal and conservation issues.
Example of mislabeling illustrated by visual comparison of salmon. - Difficulty in distinguishing between wild-caught and farm-raised salmon even visually. - Misidentifications can also happen with fish like grouper and red snapper.
Farm-Raised vs. Wild-Caught Salmon: - Farm-raised salmon has thicker fat layers, resulting in a buttery texture when cooked. - Wild-caught salmon has less fat, can be drier when cooked, and possesses a stronger fishy taste.
Red Snapper Misidentification: - Tilapia is often substituted for red snapper. - Red snapper is one of the most frequently mislabeled fishes, skewing public perceptions of its availability. - Cooking and seasoning can make it difficult to differentiate between red snapper and tilapia.
Mislabeling can occur at various points in the supply chain: - At catch time, during processing, wholesale, retail, or in restaurants. - Chefs may not be able to identify mislabeling if they purchase pre-filleted fish.
The need for an international traceability system to combat mislabeling has seen limited progress.

Morphological Identification: - Sometimes morphological features can help in identifying fish. - DNA analysis is often required to confirm identification. - Fish fillets: Skinned and cut along one side of the vertebrae; two fillets per fish. - If two left-side fillets are found, they belong to two different fish.
Importance of keeping scales and ribs on fillets for better identification. - Certain states and provinces have regulations for leaving scales on fillets.

Shape of the Fillet: - Short, wide fillets indicate different species than long, narrow fillets. - Example: Bottom fillet could be a bluegill, top fillet may be a northern pike or gar.
Color of the Fillet: - Related to fish type and diet. - Crappies: White flesh - Trout and salmon: Reddish/orangish flesh - Bullheads & pikes: Yellowish flesh - Scavenger fish (e.g., carp): Reddish layer near skin.
Rib Count: - Size and number of ribs remain useful for identification as different fishes have specific rib characteristics.
Stomach Cavity Length and Depth: Assists in species identification.
Fins and Rays: - Placement of fins can differ among species. - Examples: Dorsal and anal fins.
Other Bones: - Frequently found in fillets, especially in canned or smoked fish. - Y-shaped bones in pike family and intramuscular bones in carp, golden eye, and suckers. - Absence of bones can rule out various species (e.g., bass, crappie, sunfish).

Definition: Myotomes are segments of muscle fibers, often referred to interchangeably with myomeres.
Structure: Zigzag (W-shaped) segments, best observed from tail to head.
Two Types of Muscle Fibers: 1. White Muscle Fibers: - Contract rapidly for short durations. - Example fish: Pike, sunfish, crappie, perch. 2. Red Muscle Fibers: - Slower but sustain activity longer due to increased blood supply. - Typical in continuous food-seeking species like carp.
Method for Counting Myotomes: - Examine segments carefully for overlapping myotomes, particularly near the head for a final count.
Myotomes Charts: - Exist to reference fish species based on the number of myotomes (e.g., less than 25, 26-33).

Postmortem interval (PMI) refers to the time elapsed since the fish was caught.
PMI can be significant in determining legality during inspections in rivers, lakes, or processing plants.
Legal implications of PMI can clarify whether fish were caught within legal open seasons.
Common characteristics to note during inspections include: - Skin appearance, slime, smell, eyes, texture, rigor mortis, heart and liver condition, peritoneum state.
Charts can help determine characteristics quickly in the field without lab access. - Charts are based on research by organizations like the FAO and are helpful for assessing fish quality based on time of death.
General Approach: - Reliance on representative samples from larger quantities is important, rather than assessing just one fish, due to possible mixing by poachers. - Observations should consider the freshest and oldest fish found in a batch to estimate a broad timeframe.

Characteristics to observe over time: - 0-4 Hours: Good color, no smell. - 4-12 Hours: Still in good condition. - 12-24 Hours: Loss of skin color begins. - 48-72 Hours: Dull, fading appearance, milky slime, starting fishy smell.
Rigor Mortis - Appears within the first 4 hours, dissipates by 48-72 hours.
Important features affected by time: - Heart/liver: Bright red morphs to faded colors, extends into the timeline. - Peritoneum: Changes from glossy to signs of rib protrusion.
Suggestions for field experimentation to develop personal manuals for identifying fish PMI and characteristics at local levels.