| Summary: | This study aimed to identify morphometric relationships in fish that could serve as indicators for status on sexual maturation in Atlantic salmon (Salmo salar). To achieve this, 250 salmon were netted out and individually weighed, measured for fork length, and photographed over six months. Further, the distance between morphometric key points were digitally measured for each individual using the photographs. Gonad weight was measured in order to calculate GSI as a degree of sexual maturation status. The ratios of snout-eye length to head length, snout-eye length to fork length, head length to fork length, body-height-central to fork length, body-height-anal to fork length, anal-caudal-fin to fork length, anal-caudal-fin to body-height-central, body-height-anal to body-height-central, where analyzed. Our results reveal that the snout/head ratio and the snout/fork length ratio are statistically significant indicators of sexual maturation. Specifically, a Generalized Linear Model (GLM) test showed that the snout/head ratio, snout/fork length and head/fork length had a significant relationship with GSI in August and November. The study also unveils complex interactions between growth metrics such as length, weight, condition factor (K), and specific growth rate (SGR) with GSI, indicating that the relationship between growth and sexual maturation undergoes seasonal fluctuations. Mature fish were found to allocate energy differently from immature fish, particularly near the spawning season, confirming a shift from somatic growth to reproductive activities. Our study suggests a multi-metric approach is crucial for a nuanced understanding of salmon physiology. The findings point to specific morphometric ratios as reliable indicators for assessing sexual maturation in salmon, especially during August and November. Masteroppgave i biologi BIO399 MAMN-BIO MAMN-HAVSJ
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