Effect of Preservation in Formalin and Alcohol on the Growth Rate Estimates of Larval Northern Pike

Abstract

Body length measurements and growth rate (GR) analysis are important steps in research on the ecology of early development stages of fish. In order to obtain accurate results, the lengths of field‐collected and preserved larvae must be corrected for shrinkage. Northern Pike Esox lucius larvae were kept in the laboratory in freshwater conditions (300‐L tank; temperature = 16°C), where they were fed six times a day ad libitum with aquaculture feed. Every 3 d over a period of 30 d, a subsample of approximately 30 larvae was collected, measured, and placed in separate vials in 96% alcohol and 4% formalin. All of the larvae (8.8–34 mm SL; n = 276) were measured again after 90 d of preservation. The shrinkage ranged from 0% to 11.6%, averaging 3.42% in alcohol (n = 134) and 3.74% in formalin (n = 139). The difference was not statistically significant. In both preservatives, the relative shrinkage (%) was higher for small fish than for large fish. The length correction for 8–34‐mm SL fish in both alcohol and formalin should be done by adding 0.7 mm to the length measured after preservation. Shrinkage did not affect fish GRs estimated based on linear regression fitted to size‐at‐age data (0.645 mm/d for unpreserved larvae and 0.650 mm/d for preserved larvae). In the opposite case, when growth was estimated as mean GR between hatching and sampling, the shrinkage effect was significant: the mean GR was 0.604 mm/d for unpreserved larvae and 0.558 mm/d for preserved larvae. The presented shrinkage correction formula allows for obtaining accurate length and GR data for larval Northern Pike that should lead to conclusions that credibly support undertaking appropriate management strategies.

Effect of preservation on fish morphology over time: Implications for morphological studies

“…We also assessed changes in both the formalin and ethanol stages of preservation, as our fishes were stored in formalin for two weeks, then subsequently stored in ethanol. Our results are consistent with previous research which found that formalin preservation tends to decrease the overall size of specimens [ 3 , 6 , 7 ]. These results similarly find decreases in overall sizes of individuals, yet each body area responds to the treatment differently.…”

“…Alterations in body shape due to preservation (i.e., most commonly for fish specimens, fixation in 10% formalin then transferred to 70% ethanol for long-term storage) are manifested in a variety of ways [ 1 – 2 ]. Previous studies have found that standard body lengths are shorter after formalin fixation and ethanol preservation [ 3 – 7 ], although fish specimens treated in a 10% formalin solution tend to increase in weight [ 3 , 6 ]. More recently, geometric morphometric analyses have been applied as a tool to measure body shape related to a number of biological questions including speciation, species identification, fish-habitat association, and hybridization [ 8 – 11 ].…”

Effect of formalin preservation on studies on morphology and condition factor of the freshwater shark Wallago attu (Bloch and Schneider, 1801) using truss network system

“…The present findings revealed that the body length in W. attu decreased due to the folding and shrinkage of the body after preservation in 10% formalin. Our results are in agreement with the previous studies of Shields and Carlson (1996); Ajah and Nunoo (2003); as well as Greszkiewicz and Fey (2018).…”

Unique osmoregulatory morphology in primitive sharks: an intermediate state between holocephalan and derived shark secretory morphology

“…If permitted, the gland was removed with a scalpel by cutting through connective mesentery and the posterior mesenteric artery. Fixation (10% formalin) of these samples resulted in shrinkage of tissue and probable changes in rectal‐gland morphology (Greszkiewicz & Fey, ; Sotola et al ., ). We attempted to calculate a shrinkage coefficient for lobulate rectal glands preserved in 10% formalin to correct for potential differences in shrinkage relative to frozen digitiform rectal‐gland samples.…”