Reproductive performance of giant freshwater prawn M. rosenbergii (de man) with special reference to broodstock age, size and nutrition, egg production and larval quality

Abstract

Research into the reproductive potential of prawns is scarce and broodstock nutritional requirements are completely unknown. The present investigation is focused principally on exploring these topics.

The literature contains considerable terminological inconsistencies with respect to demarcation of the various events and stages of caridean reproductive cycles. A consistent, unified and new, precise system of terminology is proposed together with models.

Four major female morphotypes were identified in Macrobrachium sp. based on simple, visual characteristics. These morphotypes vary in moulting and spawning physiology. Presence of eggs on pleopods reduce the moulting frequency and spawning potential in M.rosenbcrgii.

A new criteria is proposed to assess the reproductive potential of Macrobrachium species based on morphotype distribution, Spawning-Moult Capacity (SMC) and Spawning- Moult Efficiency (SME). The use of SMC and SME nullifies the influence of moulting pattern on spawning potential. A spawning anomaly was observed and referred to as Spawning Deficiency Symptom (SDS).

Food ingestion in M-rnaenbergu. broodstock varied (by up to 20%) depending on the duration of feeding and nutrient content of the diets. Females efficiently ingested and digested diets containing low levels of plant and animal proteins. However, plant protein diets appear to reduce Spawning-Moult Efficiency. The validity of widely used chromic oxide and gravimetric methods for evaluation of nutrient digestibilities with M.rQSenbergii was questioned. Quantitative egg production in M.rosenbergil was more influenced by broodstock size than by age, quality of diets and food ingestion. Whilst, chemical composition of eggs was greatly influenced by the fatty acid profile of broodstock diet. Eggs showed some plasticity in accumulation of a range of (n-3) and (n-6) PUFA levels depending on dietary input. Bigger females produce larger and more uniform sized eggs than smaller females.

The egg incubation period and the nutrient reserve in newly emerged larvae (equated with resistance to starvation) were not influenced by the broodstock age, size, quality of diets or food ingestion.

A novel approach placing greater emphasis to moulting cycle of prawn is proposed and used in the broodstock nutrition study. The implications of newly adopted methods and findings were discussed with respect to broodstock management.