Ingestion,growth and development of Penaeus indicus larvae as a function of Thalassiosira weissflogii cell concentration

Penaeus indicus larvae have been successfully reared in the laboratory using Thalassiosira weissflogii, Brachionus plicatilis and Artemia salina nauplii as food, with an average survival of 95.8% from nauplius 6 to postlarva 1. The effect of T. weissflogii cell concentration on larval ingestion, development and growth (total length) was investigated. Cell ingestion rates showed a saturation response to concentration. Both maximum ingestion rates and incipient limiting levels (the lowest concentration before ingestion rates were limited) were established for the feeding larval stages. Both were found to increase with progressive increase in larval development. Maximum ingestion rates increased from 0.25×10⁴ cells. larva^-1.h^-1 during protozoea 1 to reach a peak of 1.2×10⁴ cells. larva^-1.h^-1 during mysis 3 and then declined to 0.6×10⁴ cells. larva^-1.h^-1 at postlarva 1. Incipient limiting levels (ILLs) increased from approximately 0.6×10⁴ cells.ml^-1 during protozoea 2, to 0.65×10⁴ cells.ml^-1 during mysis 1, to 1.3×10⁴ cells. ml^-1 during mysis 3 to 1.6×10⁴ cells.ml^-1 at post-larva 1. Filter feeding efficiency was found to reach a maximum during mysis 1. Filter mechanisms are discussed. Generally, the most advanced larval development per unit time occurred at concentrations at and above the ILLs, while retarded development occurred below these levels. Growth increased asymptotically with cell concentration. Incipient growth limiting levels (IGLLs; the lowest concentration before growth was significantly limited) also increased with larval development and with the exception of mysis 3 they coincided with the ILLs. IGLLs increased from 0.55×10⁴ cells.ml^-1 during protozoea 2, to 0.66×10⁴ cells.ml^-1 during mysis 1, to 0.99×10⁴ cells.ml^-1 during mysis 3, to 1.62×10⁴ cells.ml^-1 at postlarva 1. Below the ILLs where ingestion was limited, animals were significantly smaller, with larval development and growth positively correlated to ingestion rates. When culturing penaeoid larvae, ambient cell concentrations should be kept above these known limiting levels to yield consistently good larval survival and growth.