## 5 FPHs--Based Aquaculture Feeds  
Aquaculture feeds are specifically designed to address the nutritional needs of aquatic species, combining various ingredients such as marine by-products, fish oils, plant-based components, live feeds, and vegetable proteins [172]. These feeds offer a balanced diet, supplying essential nutrients like proteins, vitamins, minerals, carbohydrates, and lipids that are vital for the growth, development, and reproductive health of fish and other aquatic organisms, ensuring their overall well-being [173]. The global aquaculture feed market has experienced remarkable growth, driven by the rising demand for seafood and the need for sustainable, high-quality feed solutions across a broad spectrum of species, from finfish to crustaceans [174]. In 2023, the global aquaculture feed market reached 49.70 million tonnes and is expected to rise to 78.93 million tonnes by 2032, with a steady CAGR of 5.3% from 2024 to 2032 [175]. The expanding aquaculture industry, heightened health awareness, increased seafood consumption, and a growing focus on sustainable fish production drive this market growth. As people recognise the health benefits of fish, including its rich protein content, omega-3 fatty acids, vitamins, and minerals, the demand for aquaculture feed has risen sharply [175; 176]. Additionally, fish's reputation as a healthier option compared to red meat due to its lower saturated fat levels has further fuelled the market's expansion [177]. Manufacturers are increasingly turning to FPHs as a key ingredient due to their exceptional palatability, digestibility, and bioavailability, and ability to enhance growth, immune function, and nutrient absorption in aquatic species especially during early developmental stages or under stress conditions [178]. The primary mechanisms underlying FPH efficacy relate to their rapid absorption and multifaceted biological activity. Due to their short peptide length, FPHs bypass the need for extensive enzymatic digestion, allowing for faster uptake through peptide transporters (e.g., PepT1) in the intestinal epithelium [179; 180]. This rapid nutrient assimilation contributes to improved feed efficiency, weight gain, and muscle accretion. Moreover, bioactive peptides in FPHs exert antimicrobial, antioxidant, immunomodulatory, and anti-inflammatory effects [180]. In terms of product development, the quality and functionality of FPHs depend on the choice of raw materials (e.g., fish offal, heads, viscera), hydrolysis conditions (enzyme type, temperature, pH, duration), and downstream processing techniques such as ultrafiltration and spray drying [181]. Commercial products such as Symrise Aqua Feed's hydrolysates (derived from tuna, krill, and shrimp) and CPSP (Copalis Sea Solutions(r)) have shown consistent efficacy in improving gut histomorphology, nutrient digestibility, and pathogen resistance [182; 183; 184; 185]. Furthermore, FPHs have enabled partial replacement of traditional protein sources like fish meal or soy protein concentrate by up to 50-60% without compromising performance, contributing to circular bio economy models in the aquafeed industry [186]. As a result, FPHs are emerging as a preferred choice for both economic and environmental reasons in the aquaculture industry. Early evidence by [PERSON] et al. [187] showed that replacing part of the fish meal with FPHs made from fresh Pollock body parts (Denofa Fish Peptides, Denofa, Fredrikstad, Norway) in Atlantic salmon diets improved feed intake, growth, nutrient retention, and digestibility in a dose-dependent manner--likely due to increased palatability and peptide-driven nutrient assimilation. This pattern was echoed in subsequent studies, where the molecular weight and peptide composition of hydrolysates played a critical role in physiological outcomes. For instance, [PERSON] et al.