Aquaculture and Fisheries Management 1994, 25, 861—862 SHORT COMMUNICATION Lack of growth-stimulating effect of lactate on Atlantic salmon, Salmo salar L. G. GISLASON Icelandic Fisheries Laboratories, Vestmannaeyer, Iceland R.E. OLSEN Department of Fisheries, Finnmark College, Alta, Norway E. RING0 Institute of Biology and Geology, University of Troms0, Norway It is well established that the inclusion of various chemicals such as antibiotics into the diets of both terrestrial (Feighner & Dashkevicz 1987) and aquatic animals (Ahmad & Matty 1989) can promote growth and feed conversion. The use of such additives is controversial, however, and a search for other growth promoters is needed. Recently, Ring0 (1991) reported that the inclusion of 1% lactate into the diet of Arctic charr, Salvelinus alpinus (L.), increased growth rate by more than 20% when compared with a non-supplemented diet. Analysis of faeces indicated that fish maintained on the lactate diet had higher digestibility of nutrients while the feeding rate was unchanged. If these results are valid for other fish species of commercial value, a major improvement in economy of the individual fish fanner is likely to be achieved. The present study was undertaken in order to examine the effect of lactate on growth performance of another salmonid, the Atlantic salmon, Salmo salar L. All experiments were conducted at the Marine Biological Research Station, Troms0, northern Norway from March to August under natural photoperiod regimes. Salmon juveniles (about 8-00g) were purchased from a local fish farm. They were divided into six groups each containing 99 fish and fed a commercial diet (Tess Elite Pluss) at 1-5% of their body weight/day at 11°C for 20 days prior to initiation of the experiments. The fish were thereafter fed two test diets containing 0% (control) or 1-5% Na"*"-lactate, which were prepared from commercial diets according to Ring0 (1991). Table 1 summarizes growth data and mortality from Atlantic salmon held in fresh water. Specific growth rate (SPG) was calculated according to the formula (In end wt — In start wt) X 100/days of study. No significant differences were observed between fish fed the two diets. Similarly, no difference was seen in the faecal chemical composition (Table 2). Similar results were obtained with larger Atlantic salmon held in full-strength sea water (data not shown). In conclusion, addition of lactate to the diet of Atlantic salmon does not influence growth, mortality, or gross chemical composition of the faeces. This finding is opposed to earlier studies on Arctic charr, where significant growth promotion appeared (Ring0 1991). Accordingly the effect of lactate seems to be species dependent, probably reflecting differences in nutrient utilization or digestive processes. A more comprehensive study regarding these aspects is currently under way. Correspondence: Dr Rolf Erik Olsen, Department of Fisheries, Finnmark College, Follumsvei, 9500 Alta, Norway. 861