Tenebrio molitor larvae meal as fish meal alternative: impacts in juvenile narrow-clawed crayfish (Pontastacus leptodactylus)

Abstract

A 60-day trial examined replacing fish meal (FM) protein with defatted Tenebrio molitor (TM) larvae meal in diets for juvenile narrow-clawed crayfish (Pontastacus leptodactylus). Six isonitrogenous, isoenergetic diets with 0–100% FM protein replacement were tested on 600 stage II juveniles (four replicates of 25 per treatment).Growth performance was similar between the control and 40% TM groups (final weight and SGR did not differ significantly, p>0.05), but replacement levels above 40% significantly reduced growth and survival, with the 100% TM group showing the lowest final weight and survival (48%). Molting frequency and cheliped injury did not differ across treatments. Histological analysis showed normal hepatopancreas and intestine in the control and 20% TM groups. At ≥40% TM inclusion, hepatopancreatic damage (pigment deposits, elevated B-cell counts, degeneration, necrosis) and progressive shortening of intestinal villi were observed, along with luminal content stasis. Overall, up to 20% FM replacement with TM larvae meal can be used safely without harming growth or gut/hepatopancreas health, while higher inclusion levels risk long-term digestive tissue damage.