Lesson Notes By Weeks and Term v4 - SHS 1
BIOLOGY AND ENTREPRENEURSHIP
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BIOLOGY AND ENTREPRENEURSHIP
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Subject: Biology
Class: SHS 1
Term: 1st Term
Week: 7
Grade code: 1.1.2.LI.2
Strand code: 1
Sub-strand code: 2
Content standard code: 1.1.2.CS.1
Indicator code: 1.1.2.LI.2
Theme: EXPLORING BIOLOGY IN SOCIETY
Subtheme: BIOLOGY AND ENTREPRENEURSHIP
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Welcome, future biologists and entrepreneurs! Today, we are exploring a very practical and important topic: how our knowledge of biology can help us become successful in the fish business. In Ghana, fish is a major source of protein and income for many families, from the coastal towns like Elmina and Axim to the inland communities around the Volta Lake and various fish farms. Understanding the biology of fish doesn't end when the fish is grown. In fact, the way we harvest and process fish is deeply rooted in biological principles. Applying these principles correctly can mean the difference between profit and loss, between fresh, healthy food and spoiled, dangerous food.
This lesson is divided into two main parts: the biology of harvesting fish and the biology of processing fish. Part 1: Biological Principles in Fish Harvesting
Harvesting is not just about catching the fish. It's a careful process designed to maximize the quality and shelf-life of the fish.
A. Pre-harvest Starvation (Fasting) Practice: Fish are intentionally not fed for a period of 24-48 hours before they are harvested. Biological Principle (Digestion & Microbial Action): Emptying the Gut: The primary reason is to allow the fish to completely digest any food in its stomach and intestines. A full gut contains partially digested food, digestive enzymes, and a vast population of bacteria. Reducing Contamination: When a fish with a full gut is handled or gutted (intestines removed), there is a high risk that the gut will rupture, spilling its contents onto the flesh. These contents (enzymes and bacteria) will immediately start to break down the fish muscle, leading to rapid spoilage, bad odours, and a soft texture. Slowing Autolysis: Autolysis means "self-digestion." The fish's own digestive enzymes are powerful protein-breakers. By emptying the gut, we remove the main source of these enzymes, significantly slowing down the initial decay process after death. Ghanaian Example: A tilapia farmer in Asutsuare who wants to transport his fish to Accra will starve them for a day. This ensures the fish arrive in better condition, with firmer flesh, and are easier to clean for the market women.
B. Stress-Free Harvesting and Quick Chilling Practice: Using methods that minimize the struggle of the fish (e.g., using a seine net to gently crowd them instead of chasing them individually) and immediately placing them in ice or an ice slurry after capture. Biological Principle (Respiration, Glycogen & pH): Energy Storage: Like humans, fish store energy in their muscles in the form of a complex carbohydrate called glycogen. Stress and Energy Depletion: When a fish struggles violently during harvesting, it uses up all its muscle glycogen for energy through anaerobic respiration. A major by-product of this process is lactic acid. Effect of Lactic Acid: After death, the lactic acid builds up in the muscle, causing the pH of the flesh to drop (become more acidic). This rapid pH drop leads to a soft, poor-quality texture and shortens the duration of rigor mortis. Rigor Mortis: This is the natural stiffening of muscles after death. A fish that enters rigor mortis slowly and stays stiff for a longer period is a sign of high quality and freshness. Stressful harvesting depletes glycogen, leading to weak and short-lived rigor mortis, meaning the fish will spoil much faster. Quick Chilling (Temperature & Enzyme Activity): Placing fish on ice immediately after harvesting drastically lowers their body temperature. This slows down all biological and chemical reactions, including the activity of spoilage bacteria and the fish's own enzymes (autolysis). Every hour a fish spends at a warm temperature is equivalent to many hours, or even a day, on ice in terms of spoilage. Part 2: Biological Principles in Fish Processing (Preservation)